tune your afr and stop your MAF from maxing out for $100 [Archive]

mbtoloczko

11-03-2005, 08:26 PM

Over the last year, I've been trying to figure out how I can get some control over the air-fuel ratio and stop the MAF from maxing out quite as soon. I've come up with a solution involving two items:

1) 2000 Impreza RS fpr
2) A MAF "bypass" tube.

The Impreza RS fpr, which costs about $75, raises the baseline fuel pressure from 36 psi to 43 psi. This, in turn, richens the air-fuel ratio. Comparing my wideband O2 measurements to other people's (see Chiketd's and SVXRide's dynosheets), it looks like the Impreza RS fpr richens the afr from about 14:1 to about 12.5:1 over the 3000-5000 rpm range, and above 5000 rpm, it richens from about 13.5:1 to 11.5:1. This is a bit too rich.

So, I got to thinking about how I could lean out the afr. My first thought was an SAFC-II, but the darn things are expensive and it doesn't do anything to keep the MAF from maxing out at high airflow. I got to thinking about other ways to lean out the afr, and I realized that if I could just add small intake tube that allows some air to go from the airbox straight to the intake plenum at the entrance to the throttle bodies, then some air could get to the engine without going through the MAF. So, the total amount of air getting to the engine is the same, but the MAF signal is reduced because not all the air is going through the MAF. The result is that the ECU sends less fuel to the engine, and the afr gets leaner. Seemed like a cool idea to me. So I tried it. The picture below shows the MAF bypass installed. Its 3/4" ID rubber tubing. The fittings at the airbox and the plenum were bought at Lowe's. Total cost for tubing and fittings was $10. The fittings are cool because they have nuts to hold the fittings to the airbox and to the plenum. I had to use a bit of silicon sealant at the plenum because the plenum is not completely flat. The configuration in the picture will probably not be the final configuration. The elbow significantly reduces airflow.

http://www.subaru-svx.net/photos/files/mbtoloczko/31099.jpg

Next, I got out my LM-1 wideband meter and took some afr readings before and after installing the MAF bypass. The first graph below shows the baseline reading with no MAF bypass. You can see that the afr is around 12.5:1 from 3000-5000 rpm, and then goes even richer after that. You can also see that the MAF voltage is reaching an *average* peak value of about 4.4 volts (which is still less than the 4.8 volt max that it can produce). The second graph shows the result for an experimental bypass that I didn't end up using. The result is quite good though. The afr is leaned out to about 13.2:1 from 3000-5000 rpm and then sits at about 12.2:1 at peak rpm.

http://www.subaru-svx.net/photos/files/mbtoloczko/31047.gif

Here are the results for two other MAF bypass configurations that I tried. The first config works a bit better than the second. The second one is the configuration in the picture above. You can see that not as much air gets through the bypass because the afr is a little richer. Both configurations give about the same result though. Overall, I'm very pleased with the result. The engine is much more peppy when I step on the gas, and now don't have to worry quite so much about the MAF maxing out with further NA mods (ram air is next). If anyone is interested, I can post more detailed pictures and descriptions of the parts for the MAF bypass mod.

http://www.subaru-svx.net/photos/files/mbtoloczko/31097.gif

TomsSVX

11-03-2005, 10:49 PM

cool... we will see how well it works on a modified engine this weekend ;) As for me, the stage 2 is all I need. This mod definately helps out the OBDII guys until LAN finds a 97 that he likes

Tom

Chiketkd

11-04-2005, 07:22 AM

Great write-up Mychailo. The results definitely look great! :)

-Chike

SilverSpear

11-04-2005, 07:31 AM

Without even seeing the results, i think what he did is very logical to cope with the RS AFR. Great Mike, and a bold move ;)

AppStateSVX

11-04-2005, 07:32 AM

Is the Impreza RS the only FPR that can be swapped into the SVX? Just curious...... :D

drivemusicnow

11-04-2005, 07:48 AM

Haha... I do remember coming up with this idea for a completely different purpose. I was thinking about adding a valve in the tube however, so that you could control the amount of air that flows through the tube.

(my purpose was because of my knock sensor... which by the way, after being replaced twice, is still giving me trouble. I haven't had the chance to bust out a multimeter and start going through the knock sensor connectors to see where my problem is.)

I'm glad it worked out for you!! If you could add larger injectors, you could allow even more "unmetered" air through. Some People do this with dsms as an effective cheap way to tune their cars. (Less now, but it used to be popular)

mbtoloczko

11-04-2005, 08:41 AM

cool... we will see how well it works on a modified engine this weekend ;) As for me, the stage 2 is all I need. This mod definately helps out the OBDII guys until LAN finds a 97 that he likes

Tom

Yeah, its no Stage 2, but it does nicely compliment mild NA breathing mods (exhaust, air filter, ram air). Its more like a DIY Stage 1.2. Yeah, should provide a useful bit of MAF padding for that modified engine. :-)

Is the Impreza RS the only FPR that can be swapped into the SVX? Just curious...... :D

There might be other Subaru fprs that fit, but I haven't checked because the Impreza RS fpr gets the job done.

...

... If you could add larger injectors, you could allow even more "unmetered" air through. Some People do this with dsms as an effective cheap way to tune their cars. (Less now, but it used to be popular)

Yeah, I thought about a larger tube, but there's not much room to add a larger tube in the path I used. If someone wanted to add a tube that entered into the driverside of the intake pipe, a larger tube could be used there and then perhaps routed into the driverside fenderwell. At some point though the reduced MAF signal from a larger tube is going to lead to too much timing advance.

Earthworm

11-04-2005, 12:11 PM

SilverSpear

11-04-2005, 01:04 PM

Are those Grey joints hard enough not to melt or change shape?

Chiketkd

11-04-2005, 01:25 PM

Who was the first person to mention this idea? I know I mentioned it shortly after LAN realized we were maxing out the MAF. I remember discussing with Chike that the only way to fix the MAF is to either replace it with one that could read higher flow or allow a controlled amount of air to bypass the MAF.

Cool to see it works! :D

Are you going to market this?
I remember that thread. However, through some PM's I've had with Mychailo, he's been tossing this idea around for quite some time. Glad to see it come to fruition and be successfull.

Maybe it'll finally prove to people what I already knew from my runs last Friday - my MAF maxed out! :)

-Chike

drivemusicnow

11-04-2005, 02:27 PM

Yeah, its no Stage 2, but it does nicely compliment mild NA breathing mods (exhaust, air filter, ram air). Its more like a DIY Stage 1.2. Yeah, should provide a useful bit of MAF padding for that modified engine. :-)

Yeah, I thought about a larger tube, but there's not much room to add a larger tube in the path I used. If someone wanted to add a tube that entered into the driverside of the intake pipe, a larger tube could be used there and then perhaps routed into the driverside fenderwell. At some point though the reduced MAF signal from a larger tube is going to lead to too much timing advance.

You might be able to use a seperate filter like those used as crankcase vents. The biggest problem you need to avoid is if the "unmetered" air has less resistance than the metered air.. this would result in possibly not idling

Earthworm

11-04-2005, 02:37 PM

Resistance won't be an issue as the air is taken AFTER the air filter.

mbtoloczko

11-04-2005, 04:21 PM

...

Are you going to market this?

Since the parts are so easy to find, and its so easy to make, I'm not sure that anyone would want to buy a kit. The hardest part was drilling the airbox and the intake pipe, and that was actually more time consuming than it was difficult because I didn't have a large enough drill bit on hand and used a dremel tool to open up the holes.

With that said, if anyone wants a MAF bypass "kit", I'd be happy to gather up the parts and mail them out to whoever wants it. Should probably cost about $20/kit including postage. The Impreza RS fpr would have to be bought at your favorite Subie dealer. I can post the PN if anyone is interested.

Are those Grey joints hard enough not to melt or change shape?

I was thinking about that last night. Those gray plastic joints are made of a thermoplastic material, so I can heat one up and reshape it. I'll give it a try on Saturday morning.

I remember that thread. However, through some PM's I've had with Mychailo, he's been tossing this idea around for quite some time. Glad to see it come to fruition and be successfull. ...

The first person I know of to realize that the MAF is maxing out was Porter back in August, 2003.

http://www.subaru-svx.net/forum/showthread.php?t=12611&p=139768

I think that the first time I saw anything on the SVX board about a bypass was something written by drivemusicnow.

TomsSVX

11-04-2005, 07:56 PM

You might be able to use a seperate filter like those used as crankcase vents. The biggest problem you need to avoid is if the "unmetered" air has less resistance than the metered air.. this would result in possibly not idling

idling won't be an issue. The MAF is next to unused at idle as the air intake is controlled by the IAC and the SIAC. The SAIC is the cold start idle controller and the IAC is just the idle air controlled. It is a small rotating valve on the bottom of the throttle body. Any unmetered air at idle would need to come into the engine after the butterflies...

Tom

AppStateSVX

11-04-2005, 11:50 PM

I just bought a 2002 WRX FPR today on ebay, I got it for pretty cheap. Does anyone know if this will work? I hope so, haha :D

SilverSpear

11-05-2005, 12:42 AM

I was thinking about that last night. Those gray plastic joints are made of a thermoplastic material, so I can heat one up and reshape it. I'll give it a try on Saturday morning.

If they do, just get heat isolating material and cover them with it. Also the Heat isolating duct tape will work, same as I did with my copper intake... BTW i will post new pics about it very soon.

Myxalplyx

11-05-2005, 04:56 AM

Very nice thread and great info Mychailo. You do realize that this info can spread like a disease to other forums for other models of Subarus right? The later modelled turbo'd Subarus of the late 80's has problems with fuel cut due to the Maf voltage reaching a certain point. If this mod could prove successful in application on these turbo'd subarus, the bypass can keep the airflow at bay by not letting too much air through the maf sensor during WOT thus preventing a fuel cut. Of course a valve can be put in line to regulate how much air can bypass. Also, you could have more than one bypass or use bigger diametered tubing, just in case not enough air bypasses.

Interesting! I posted a thread a USMB today.
http://www.ultimatesubaru.net/forum/showthread.php?p=365547#post365547

Thanks for the info.

SVXRide

11-05-2005, 07:38 AM

Myxalplyx

11-05-2005, 09:27 AM

One word of caution on the bypass mod -- everyone should notice that Mychailo took a very scientific/engineering approach to the process and used a wide band to measure exactly what the the bypass was doing to the AFR. As a result, we (the SVX community) have a baseline system that we can copy and not have to worry about burning up our engines due to overly lean AFR. The last thing you want to do in this area is adopt a "larger tube is better" approach :eek:
-Bill

I understand fully. I mentioned that it would probably be advisable to use a wideband, EGT guage or a dyno when doing this mod. My thinking is flawed though. On a boosted car, the boost pressure would push outward from the bypass instead of sucking the air in from the bypass. That is for another thread/another forum. Thanks anyways! Carry on! :)

mbtoloczko

11-06-2005, 09:01 PM

Went looking for better tubing and found what looks to be ideal. Its the tubing that is actually meant to be used with the fittings. :-) The tubing is flexible yet kink resistant. All the parts are by Carlson Electric. Its 3/4" dia hose and fittings. I found that if I heated the tubing at around 150F in the oven for a few minutes, its much more flexible and easier to install.

Drove the car this evening, and its running great. The idle was a little loppy when I first started the car but after a bit of driving, it steadied out. Seems that initially, the ECU was running the afr a little lean at idle, and when it would swing way lean, the idle speed would take a dip. Under agressive driving, the afr is right around 13.2:1 from 3000-5000 rpm. I'll post a log tomorrow.

http://www.subaru-svx.net/photos/files/mbtoloczko/31158.jpg

drivemusicnow

11-06-2005, 10:47 PM

I understand fully. I mentioned that it would probably be advisable to use a wideband, EGT guage or a dyno when doing this mod. My thinking is flawed though. On a boosted car, the boost pressure would push outward from the bypass instead of sucking the air in from the bypass. That is for another thread/another forum. Thanks anyways! Carry on! :)

You're over thinking it... All you have to do is bypass the MAF... even if you let the air enter 3 inches after it, you're effectively letting unmetered air in, and therefore causeing the car to go leaner. This would then be before a turbo, and it wouldn't cause any problems.

I still think the valve idea would be the best way to do it. It would effectively be an AFC and would allow you to run at whatever A/F ratio you wanted (fitting the stock maps and not knocking)

I think someone looking into a turbo setup could use this pretty effectively. maybe even use a throttlebody from the junkyard, attach it after the MAF to the intake tube. (before the turbo if its a turbo car, have a similar, or more restrictive filter) and voila! insta air fuel control. you could even get all fancy and have an electronically controlled actuator to control the TB valve. I would however suggest making sure your knock sensors are in perfect working order before you tried this. (Maybe that J&S safeguard or whatever its called)

SilverSpear

11-06-2005, 11:26 PM

I wonder if the H-6 cover still fits without touching the tube :rolleyes:

Earthworm

11-07-2005, 01:22 PM

I wonder if the H-6 cover still fits without touching the tube :rolleyes:It's all how you decide to build it. All you need is enough hose to get around the MAF. You don't have to run all the way to the throttlebody.

Hocrest

11-07-2005, 01:37 PM

What would the ~60 psi FPR out of an XT6 contribute to this??? I'll ship one out if anybody with the proper meters wants to play ;)

mbtoloczko

11-07-2005, 05:48 PM

What would the ~60 psi FPR out of an XT6 contribute to this??? I'll ship one out if anybody with the proper meters wants to play ;)

A 60 psi fpr will push about 30% more fuel into the motor. To get 30% of the air to go around the MAF, the bypass tube would have to be roughly 1.5" in diameter. I think that there would be some major issues with idle and timing advance with that much air going around the MAF.

Hocrest

11-08-2005, 12:41 PM

What would the ~60 psi FPR out of an XT6 contribute to this??? I'll ship one out if anybody with the proper meters wants to play ;)
I was corrected, according to the FSM's the XT6 fpr is 43.5 psi.

Chiketkd

11-09-2005, 01:07 PM

mbtoloczko

11-09-2005, 03:12 PM

Mychailo,

This new version looks terrific. Did you get a chance to do that log? :)

-Chike

Haven't had a chance to do the log yet, but I can say that the car is much more peppy compared to no bypass tube, and my real-time observations of the afr readout on the LM-1 put the afr at around 13.2:1 in the 3000-5000 rpm range. As a bonus, it seems that the engine stalling issue I've had since installing my 5MT has been somewhat reduced since I installed the bypass. The only negative that I can see so far is that idle is loppy when the motor is cold. The loppy idle is caused by fairly large swings in the afr. I can watch it swing from 13.5:1 to 15.5:1 during cold idle. It doesn't stall though. Just loppy. On a side note, this leads me to conclude that the MAF does play a role in controlling idle, and going to a larger tube may result in a very uneven idle even when the engine is warm.

Anyhow, I'll try to get a log tonight.

mbtoloczko

11-11-2005, 08:47 AM

After a few more days of driving with the MAF bypass, I have found that when the engine is not up to full temperature, there is some tendency for the engine to stall, at least with my 5MT. No stalling problems when the engine is stone cold, and no problems when the temperature needle is in the full warm spot, but about halfway between stone cold and full warm, there is some tendency. Putting a slight restriction in the bypass line should fix it.

Phast SVX

11-11-2005, 09:58 AM

drivemusicnow

11-11-2005, 11:37 AM

Phast SVX

11-11-2005, 09:24 PM

I see a use for a temp controlled valve... seems like it would work... Or RPM controlled, however that would be harder.
or just buy a stage 2 and do it the right way without messing around!!!
phil

AppStateSVX

11-11-2005, 09:38 PM

or just buy a stage 2 and do it the right way without messing around!!!
phil

the whole point behind this is for those of us who can't afford Stage 2, or, in the case of the OBD-II guys it isn't available for :)

drivemusicnow

11-11-2005, 10:09 PM

or just buy a stage 2 and do it the right way without messing around!!!
phil

and i thought you used to be a dsmer :( :( :(

Just kidding haha. Seriously though, just for having your MAF not max out, running a say, 100*F temp switch (20$) that opens and closes a valve (20$) in a tube that bypasses the MAF (10$) seems cheap.

Although I'd kinda like to know why subie would use the MAF to control idle...

Anywho. its all good.

TomsSVX

11-11-2005, 11:06 PM

I don't believe the MAF is used during idle... Mychailo you have the ability to monitor MAF voltage...what is the reading at cold idle and warm idle?? also some in between. The Idle Air Controllers should handle that as the engine runs in open loop when warming up and closed loop when fully warm and shutting off the SIAC and using only the IAC to function for breathing at idle. This is only an assumption so don't chew me out for it...

I agree that the Stage 2 is the proper thing to do for anyone with OBD I but the OBD II guys might be able to utylize this.

Tom

KCROGUEDOG

11-12-2005, 01:59 AM

i like this idea. so i was reading the charts and is it better with the hose spliced or just curving around everything. i still need to figure out where to drill into my cold air intake that runs in the fender. how big of a hose is to big to use?

mbtoloczko

11-12-2005, 09:01 AM

I'll get some data logs tomorrow. I'll do one with the engine stone cold, then one when its lukewarm, and then when its full warm.

My general observations are that the engine switches to closed-loop fairly quickly after the car is started. It generally takes only two minutes before its running in closed-loop. When the car is lukewarm, there is a tendency when the car is idling for the afr to swing from ~13:1 to as high as 17.5:1, and the stalls occur when it swings super lean.

KC, I'd recommend first trying 3/4" ID. That's the largest you'll want to use with an Impreza RS fpr. If you install an adjustable fpr and go with a higher fuel pressure, then you can try larger diameter hoses as you increase the fuel pressure, but you'll have to be very careful about building in too much ignition advance.

KCROGUEDOG

11-12-2005, 09:09 AM

i see i see ty

UberRoo

11-12-2005, 03:17 PM

One thing that has not been discussed is that the smaller bypass tube has fluid-dynamic (aerodynamic) differences other than just being smaller than the main intake tube. If you were to plot the flow resistance over airspeed, you'd notice that the resistance will increase on a curve. If you compared the curve of the main intake tube to the bypass tube, the curves will be different. (The small tube will have a much steeper curve.)

Here's another way of saying it: Let's presume the total area of both tubes is 10 square inches. Let's say the small tube is one square inch and the large tube is 9 square inches - 10% and 90% respectively. At idle, each tube will handle almost exactly their respective percentage of air flow. At higher air speeds, the small tube will handle a lower percentage, say 8% while the large tube will handle more, 92%. At the extremes, the difference could be so large that the small tube might as well not even be there. Honestly, I don't have any precise values. It might be negligible, but then again, it might not. Those joints and right angles in the small tube won't have much effect at low flow rates, but at high rates it'll really add up. The smaller diameter alone will make a difference simply because the aerodynamics are different on a smaller scale. It sounds like the primary goal is to fix a problem that occurs at higher speeds. Unfortunately the bypass tube will function best at lower speeds. Perhaps you could install a vacuum-actuated valve in the bypass tube that opens when the engine is under load, or maybe a vacuum-actuated electrical switch that changes the output value of the MAF.

Just something to think about.

shotgunslade

11-13-2005, 10:57 AM

That's absolutely true, UberRoo. I figure that at 6000 rpm the engine is drawing about 350 cfm of air (the volume of air at standard temperature and pressure would be a little less because of reduced pressure in the intake tube). The inside diameter of the intake tube is about 3", giving it a cross sectional area of about 0.05 sqft. That means the average velocity in the intake tube is about 7000 fpm. Pressure drop across the intake tube at that flow is about 0.03 psi, including the bend, but not including the corrugations (I can't figure that until I do the CFD). An equal pressure drop through a 1 inch tube would yield between 16 and 18 cfm (only about 3200 fpm average velocity). So, even though the cross sectional area of the 1" tube is 11% of the 3" stock intake tube, the flow rate through it would be only 5% of the amount flowing through the main tube at 6000 rpm. That's because the wall/flow area is so much greater in the smaller tube, so that frictional losses rise much more quickly in the smaller tube as flow and velocity increase.

shotgunslade

11-13-2005, 06:51 PM

Made a big conceptual error in my last post. Forgot about velocity pressure. It takes a lot of pressure difference to get the air in the intake tube moving at 7000 fpm; in fact, the velocity pressure of 7000 fpm is over 1.3 psi. So, if you look at the total pressure required to push flow through the two tubes and balance them, you wind up with 332 through the 3" duct and 28 through the 1" ID bypass duct. If you use a 3/4" ID line to bypass the MAF, you'll get about 15 cfm going through the bypass and 335 cfm going through the main line at 6000 rpm.

At 1000 rpm, you would be pulling a total of 58 cfm through the intake system, and about 53 would be going through the MAF and 5 cfm would be going through the bypass. With a 3/4" ID bypass, you would wind up with about 2.5 cfm going through the bypass and 55.5 cfm going through the MAF.

mbtoloczko

11-14-2005, 10:40 AM

Dan,

Your numbers say that at both 1000 rpm and 6000 rpm, about 4.3% of the air will go through the MAF bypass. Is this correct?

Finally had time this weekend to get the MAF and AFR data for the smooth tube configuration. Results are excellent. From 3000-5000 rpm, the afr is right around 13.2:1 which is right about where it should be for maximum power, and then from 5000-6500 rpm, it settles at about 12.4:1 which is also pretty good. Nothing that can be done about the richening of the afr past 5000 rpm. The ECU is doing this for some reason. It shows up in the non-bypass afr curve too. If I compare these afr results with the non-bypass AFR data, it looks like about 5% of the air is going through the bypass tube regardless of air speed which is right in line with Dan's predictions (if I interpreted them correctly).

http://www.subaru-svx.net/photos/files/mbtoloczko/31494.gif

mbtoloczko

11-14-2005, 11:09 AM

Here are the MAF, AFR, and rpm data vs time for cold start and engine full warm. For the cold start condition, the afr starts swinging up and down when the ECU goes into closed loop mode. For temperatures below probably 40F, the swings can become great enough that the engine will stall. If I compare the position of the spikes in MAF voltage, rpm, and AFR, it appears that the spike in the MAF voltage just slightly precedes the spike in the AFR data. That would suggest to me that the AFR is affected by the MAF signal. It would seem more logical to me though that the afr fluctuations are preceding the MAF and rpm spikes. I would have guessed that the ECU is trying to lean out the afr, and the lean condition is killing power which causes the rpm to drop and the MAF voltage to drop. Anyhow, as best as I can tell, the car doesn't stall during warmup if the air temp is above about 40F.

http://www.subaru-svx.net/photos/files/mbtoloczko/31496.gif

sperry

11-14-2005, 11:49 AM

shotgunslade

11-14-2005, 12:19 PM

Mychailo:

Yes. That's what my numbers say. One thing I'm not taking into account is that you are bypassing the corrugations on the main intake tube. I really want to know what is the effect of these on flow, but our CFD shop is booked up with one of my projects for the next week or so. Have prepared measured drawings of the intake snorkus to input to the computer, just don't have a worker and workstation to spare right now.

SVXRide

11-14-2005, 12:55 PM

Just an observation. You could potentially shorten the bypass dramatically by making it only long enough to go from the airbox to just after the MAF. By shortening the length, I believe you would reduce the low-speed vs. high-speed airflow difference, and perhaps help keep the top end AFR closer to 13.0.

Instead of tapping the plenum, just tap the elbow right after the MAF (see picture). Just make sure things are as smooth as possible on the inside of that elbow, or you could be doing more harm than good!

BTW: This is some nice creative, old school, engineering. :D

tapping in after the MAF basically just "reroutes" air already in the flow stream - i.e. the MAF has already sent a signal to the ECU based on this flow passing through it. By tapping into the airbox, you are adding air - post metering - to the flow, thus effectively leaning out the mixture.
-Bill

Earthworm

11-14-2005, 01:03 PM

Bill, I'm not sure if you understood his suggestion. He wants the added hose to terminate in the circle in his picture...not start.

mbtoloczko

11-14-2005, 01:29 PM

KCROGUEDOG

11-14-2005, 02:44 PM

my thoughs exactly on entry. if i had a extra i would send one i can look around though. the goal is to bypass it but is throwing the extra in the bigger area (by the throttle body) more effective or into a elbow (right after the maf) which is packed with air already? or would that even matter?

mbtoloczko

11-14-2005, 02:58 PM

SVXRide

11-14-2005, 03:01 PM

Bill, I'm not sure if you understood his suggestion. He wants the added hose to terminate in the circle in his picture...not start.

David,
You're right....I read the post too quickly...good catch!
-Bill

sperry

11-14-2005, 08:16 PM

It would be an interesting comparison. From what SGS has said, I'm guessing that my current configuration may be the more effective one for a couple of reasons. First, I think that SGS is suggesting that the corrugations in the main pipe will further inhibit flow in the main pipe at high air velocities. This would increase the percentage of air going through the bypass tube at high rpm. Second, it may be difficult to smoothly merge the airflow from the bypass back into the main pipe right after the MAF. Third, I'm also wondering if having the bypass tube end near the throttle bodies causes a strong pull on the air going through the bypass. All just guesses though. To know for sure, I can test it, or maybe SGS can model the main pipe and the bypass together. :-))

All very good points. My thought was simply to increase the airflow around the MAF while keeping as much of the stock intake's characteristics. Similar to the 5.0L Mustang guys that swap in the larger MAF from the Ford Lightning.

On another note... how does the bypass effect the IRIS system? Isn't the IRIS designed w/ a specific length/volume intake for resonance purposes?

marlettpat

11-14-2005, 10:29 PM

im not real technical, but basically what im gathering from this is that if you have a "ram air", this would help?

sperry

11-14-2005, 10:52 PM

im not real technical, but basically what im gathering from this is that if you have a "ram air", this would help?

It's not directly related to "ram air". The idea there is simply to use the velocity of the car to compress the air entering the intake... unless it's very specifically designed, ram air doesn't really help all that much, and then it only helps at relatively high speeds.

The MAF bypass is designed to prevent the MAF (Mass Air Flow meter, it measures the amount of air entering the motor) from "maxing out". Basically, if the car is running at high load/rpms, there is the possibility that MAF won't be able to accurately measure all the air coming into the car, which can cause a problem for the ECU as it attempts to calculate the amount of fuel needed for combustion.

So, if you let some ari flow around the MAF, you can provide the motor with plenty of air w/o the MAF maxing out. However, this is very dangerous because if there is air entering the motor that the ECU doesn't know about, the motor will run lean and blow itself up! To counter this, a higher pressure fuel pressure regulator (FPR) from an Impreza is used to bump the amount of fuel that's dumped in the motor.

Getting a balance between the extra fuel and extra air is a delicate procedure, which mbtoloczko is attempting to measure with his wide-band 02 sensor, as he tries different bypass configurations in an attempt to find the ideal setup to match his FPR.

The ultimate goal is to give the motor more air and the matching amount of fuel so that all the air is burned during the combustion cycle, because air = power. Which is why people try things like ram air, turbos, superchargers, NOS, etc... they're all ways to get more oxygen into the motor.

Myxalplyx

05-09-2007, 07:28 PM

The ultimate goal is to give the motor more air and the matching amount of fuel so that all the air is burned during the combustion cycle, because air = power. Which is why people try things like ram air, turbos, superchargers, NOS, etc... they're all ways to get more oxygen into the motor.

Yeah, I like raising threads from the dead. ;) ECUTune is here but not for OBDIIs right? ***Unless I have really been out of the loop***

Why not put a voltage resister inline between the maf sensor and ECU that will not allow voltage to be read up to the voltage cap (4.5 volts it is right?)? Just thinking out loud since I can see the power die off on the dyno run I did, when the maf supposedly maxed out.

Yeah, this is old news but I couldn't find out who have done this while searching. I will continue. :cool:

It's Just Eric

05-09-2007, 08:39 PM

This thread is actually worth resurrecting

mbtoloczko

05-09-2007, 10:54 PM

Yeah, I like raising threads from the dead. ;) ECUTune is here but not for OBDIIs right? ***Unless I have really been out of the loop***

Why not put a voltage resister inline between the maf sensor and ECU that will not allow voltage to be read up to the voltage cap (4.5 volts it is right?)? Just thinking out loud since I can see the power die off on the dyno run I did, when the maf supposedly maxed out.

Yeah, this is old news but I couldn't find out who have done this while searching. I will continue. :cool:

Unfortunately, adding a resistor would not fix the situation. The problem is that the MAF has a limit on how much flow it can detect. Once the flow exceeds that value, then the MAF output stops increasing. The bypass fixes the problem by allowing some of the air to get to the motor without going through the MAF. The only problem I found was that it does mess with the idle in very cold weather.

There is another way to handle the situation. For some other cars, people will cut the MAF sensor out of the stock body and install it in a larger diameter body. The problem here is that air flow vs MAF voltage is highly dependent on the geometry of the MAF tube. Small perturbations in geometry can affect that correlation and the afr.

Myxalplyx

05-10-2007, 09:32 AM

Unfortunately, adding a resistor would not fix the situation. The problem is that the MAF has a limit on how much flow it can detect. Once the flow exceeds that value, then the MAF output stops increasing. The bypass fixes the problem by allowing some of the air to get to the motor without going through the MAF. The only problem I found was that it does mess with the idle in very cold weather.

There is another way to handle the situation. For some other cars, people will cut the MAF sensor out of the stock body and install it in a larger diameter body. The problem here is that air flow vs MAF voltage is highly dependent on the geometry of the MAF tube. Small perturbations in geometry can affect that correlation and the afr.

Thanks for clearing that up for me. I thought that once the maf hit a certain voltage (4.5volts), that it screwed up the air/fuel ratio and/or timing on purpose to protect the engine (Like the old school turbo fuel cuts). I also thought that Subarus typically did not measure air/fuel ratio during WOT but had a pre-calculated table for air/fuel ratios. I thought it only measured air/fuel ratio and adjusted for this at idle and other non-WOT moments. Interesting!

Now to start trouble! I was thinking that perhaps the ECUtune software/Z32 maf combination would address the issue I saw that happens with power output above 5500rpm. Looking at the dyno chart on their site, it doesn't. (Here's where you guys shoot me at). This leads me to believe that the problem above 5500rpm is not because the volts max out but because the engine is not getting enough air going through it. Something 'is' restricting it somehow. Turbulence, air flow discrepancies.....I dunno. Something!!! (U already know I think it is the intake). I will post up an example of this on a before and after dyno chart of another Subaru I have after I get chewed up a few posts. :D

YourConfused

08-12-2007, 01:17 AM

After reading all this so far I am wanting there to be a page 5. Too bad I can't contribute anything to this thread.

nightrider

08-12-2007, 05:45 PM

can this mod increase my hp/torque or just prevent me from looseing any at high speeds?

michael

08-12-2007, 09:41 PM

Similar to the idea of routing the bypass from the airbox to right behind the MAF. Why not play with different sized breathers where it's routed now. This would cut down on varying velocity speeds.

Trevor

08-13-2007, 05:36 AM

Consider how the MAF transducer works. Those aware of the what is involved please skip this data. (I have been nastily accused of copying and pasting text from other sources and in particular the internet. What follows I have posted previously and it is copied and pasted from my files, but I am the absolute originator of same.) :(

------ MAF measurement is achieved by heating with an electric current, a wire/gauze/grid whatever, that is suspended in the engine’s air stream. The wire's electrical resistance increases with the temperature, which limits electrical current flowing through the circuit. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wire’s temperature increases until the resistance again reaches an equilibrium.

N.B. The amount of current required to maintain the wire’s electrical resistance, is directly proportional to the mass of air flowing past the wire.

If air density increases due to an atmospheric pressure or temperature change, but the moving air volume remains constant, the denser air will conduct more heat from the wire, so that as a result, higher mass airflow will be indicated, thus offsetting what could otherwise constitute an error. -------

Having gone through this thread I have withdrawn the most pertinent points:-

“I've been trying to figure out how I can get some control over the air-fuel ratio and stop the MAF from maxing out quite as soon.”

“The problem is that the MAF has a limit on how much flow it can detect. Once the flow exceeds that value, then the MAF output stops increasing. The bypass fixes the problem by allowing some of the air to get to the motor without going through the MAF. The only problem I found was that it does mess with the idle in very cold weather.”

The suggestion has been to bypass the MAF, which must result in upsetting calibration, leading to methods ot trying to overcome this obvious defect in the proposal.

It occurs to me that if a deflector was fitted at a distance in front of the transducer, the mass of air flowing through the transducer, as a proportion of the main flow, could be reduced. It would seem that the ratio of this reduction would increase with velocity, and this should fall into line with that which is required. At idle and restricted throttle openings there could be very little affect. The distance the deflector is ahead of the transducer would have a marked affect in this regard.

Therefore there would be two contingencies providing fine tuning and requiring experiment. Size and aerodynamic shape of the deflector and distance ahead of the transducer.

It will be argued that a deflector will inhibit airflow at full throttle, but as it should not be required to exceed the area of the existing transducer and mounting assembly, this should not prove of consequence.

Trial and error would again be the order of the day, but surely would involve a great deal less work than the proposed bypass set up and it appears to me to be a more logical approach. Would it work? :confused:

Trevor

08-16-2007, 04:36 AM

This rather interesting thread appears to have been bypassed, but meantime the the subject has been irritating my grey matter. :rolleyes:

The Final output signal in the form of a varying voltage of, I gather from approximately 1 - 4.5 volts, is the product of internal electronics in front of the actual transducer. I would suspect that each MAF requires fine tuning during production, and there could well be a resistor which is adjustable, or is interchanged, so as to cater for tolerances and component variations.

As I recall, a member has posted to the affect that what could be termed the amplifier, is easily exposed by unsoldering a cover plate. If someone could examine same, there may be evidence relating to what I suggest.

If this hunch is off line, it could still be on to make a change, or add a component, in order to modify the output parameters. What is required is the internals drawn as a schematic, so that analysis is possible. Any takers? ;) However often much is hidden within an IC, making critical information impossible to obtain. :(

An alternative and simpler but cruder line of attack, is to modify the signal at the output terminal, but this could unduly adversely upset the parameters. However the problems in this respect are unlikely to exceed those involved with an air bypass arrangement. What is more a throttle operated switch, could be easily incorporated, so as to override any added circuitry, until full or near full throttle.

There are very cheap voltage regulator IC’s available, which could be used to limit the output signal to a fixed 5 volts, as well as types which could be adjusted to requirements, by means of an associated potentiometer. This is rather extreme lateral thinking, but not all that out of line. :rolleyes:

Does anyone have figures indicating the maximum voltage of the output signal at full airflow and an idea of the current involved? The latter not so important as it can be expected to be mimimal. Both could be easily measured with an engine in operation. A low impedance voltmeter would be prudent requirement in this regard.

Exactly applicable comments will be awaited with interest.

Phast SVX

08-16-2007, 11:42 AM

Phast SVX

08-16-2007, 11:46 AM

Does anyone have figures indicating the maximum voltage of the output signal at full airflow and an idea of the current involved? The latter not so important as it can be expected to be mimimal. Both could be easily measured with an engine in operation. A low impedance voltmeter would be prudent requirement in this regard.

Exactly applicable comments will be awaited with interest.

IIRC, the stock MAF meter increases too and becomes irratic over 4.7v, as measured by Sam(SVXtasy) via his greddy emanage ultimates log. This has been varified, by mychailo in another thread, and sparked him to creat his bleader valve.

Trevor

08-16-2007, 04:42 PM

why not simpler approach that is more effective then bleeding air(not a good idea) and far easier then adjusting the voltage side of things.

One small but important aspect you are leaving out of this equation of your definition Trevor is the intepretation of the voltage can be overcome by increasing or decreasing the diameter(ultimately volume) that the meter resides in.

The ECU is using this constant to properly calculate airlfow into the engine based on the voltage the meter supplies. While this trick works better for hot-foil meters, its nothing a little R&D couldnt take care of. Note: Like the rest of the proposed adjustments, this will no doubt affect the timing. How much? small adjustments not too much, increased diameter 33% and installing 33% larger injectors(370cc nissians lets say it is a straightline relationship for ease, you may want to increase the radius by 30% and injectors by 33% to obtain your desired air fuel ratio in closed loop), and I really would be afraid to watch you take off on your maiden beat run.

food for thought

Phil,

You say ---- " One small but important aspect you are leaving out of this equation of your definition Trevor is the intepretation of the voltage can be overcome by increasing or decreasing the diameter(ultimately volume) that the meter resides in.

In my first post you will see that I agree that the best approach is likely to be in relation to altering the ratio of air flow to output signal, and this is the exact feature of my suggestion involving a deflector to shield the transducer. This idea was in fact put forward as a still simpler alternative to altering the diameter of the body, such that a proportion of air will flow outside of the transducer.

I also agree that messing with the MAF signal is a far from ideal and adjusting parameters can never be exact and caution will be the name of the game.

We are on the same wave length. Trevor. ;)

Trevor

08-16-2007, 05:08 PM

IIRC, the stock MAF meter increases too and becomes irratic over 4.7v, as measured by Sam(SVXtasy) via his greddy emanage ultimates log. This has been varified, by mychailo in another thread, and sparked him to creat his bleader valve.

Phil,

I would expect that the maximum operative cut off point for the signal would be 4.5 volts, so that in excess of this would have no affect. Whatever, stumbling in the dark will never produce answers relative to any modification involving the electrical signal, so would you please point me to the thread you have mentioned.

Thanks, Trevor.

XT6Wagon

08-18-2007, 01:57 AM

MAF diamiter vs Flow is highly non-linear. even worse sensor height in the body is also higly non-linear.

For example, lowering the sensor hieght in a stock diamiter maf-body just a little bit produces a large change in the reading. AKA why you can have "fuel tuning" with aftermarket MAF bodies for the WRX with stock diamiters. Even worse Subaru has gone to highly asemetrical bodies for the LGT and whatnot.

I'm not sure how it does it, but the unichip does its tuning by screwing around with the MAF voltages the ECU sees. So you can space the sensor on a normal body, get more headroom, and then pull down if you need to.

Even better if someone can find a cheap "translator" that has plenty of RPM/load points you can skip the stock MAF setups altogether and just run a Ford aftermarket MAF body and sensor. AKA what many people with those old worthless flapperdoor MAFs do. Course the kit for the BMW's I saw was nearly the same cost as a cheap stand alone so....

=============================
On the FPR, you can just stuff in a nice rising rate FPR (with 1:1 ratio please) into the return fuel line. The stock FPR just makes for a "floor" you can't set the fuel pressure below, but once you go over that, the added regulator does all the control. Done this on a good many cars. Even got a AVO500 to 22psi with good fueling by doing a FPR this way behind my stock FPR on my STi.

For really high HP setups you may want to replace the stock FPR with just an outlet pipe. I've seen a FPRless outlet pipe somewhere, but forgot what it was on. Likely a nissan of somekind. I know my XT6 engine swap the stock FPR was having hell with the fuel pump as it was sized for far more than it was designed to handle. Poor thing was screaming.

Phast SVX

08-18-2007, 07:57 AM

MAF diamiter vs Flow is highly non-linear. even worse sensor height in the body is also higly non-linear.

Even better if someone can find a cheap "translator" that has plenty of RPM/load points you can skip the stock MAF setups altogether and just run a Ford aftermarket MAF body and sensor. AKA what many people with those old worthless flapperdoor MAFs do. Course the kit for the BMW's I saw was nearly the same cost as a cheap stand alone so....

=============================
On the FPR, you can just stuff in a nice rising rate FPR (with 1:1 ratio please) into the return fuel line(top left of the picture, mounted under the CC). The stock FPR just makes for a "floor" you can't set the fuel pressure below, but once you go over that, the added regulator does all the control. Done this on a good many cars. Even got a AVO500 to 22psi with good fueling by doing a FPR this way behind my stock FPR on my STi.

For really high HP setups you may want to replace the stock FPR with just an outlet pipe. I've seen a FPRless outlet pipe somewhere, but forgot what it was on. Likely a nissan of somekind. I know my XT6 engine swap the stock FPR was having hell with the fuel pump as it was sized for far more than it was designed to handle. Poor thing was screaming.

As i said, this works much better on a hot-foil sensor, and a little R&D would do the trick. The straightline relationship was for ease of discussion...... Going the MAF translator route is pointless, these injectors are not worth the trouble, far too small.

Regarding the RRFPR....

with stock SVX injectors its not a good option. The ~272cc injectors do not perform well over 75% DC, as with any side feed setup.

I used a Vortech RR when running 3.5lbs of boost for a while. I assume you meant an Adjustable rate fuel pressure regulator, since you are saying 1:1, meaning no pressure rise?
http://www.subaru-svx.net/photos/files/Phast_SVX/35676.jpg
i used anywhere from 7-12:1 discs while tuning. from a roll the RRFPR is horrid, dropping under 10:1 (my wide-band was reading in the 10's but as we all know a Bosch is not good for reading much under 10.5:1) accurately in the lower RPM range, to keep fuel safe up top. It functions decently for drag racing, but just dosn't cut it with the amount of pressure required on our rig.

Phast SVX

08-18-2007, 08:15 AM

Phil,

I would expect that the maximum operative cut off point for the signal would be 4.5 volts, so that in excess of this would have no affect. Whatever, stumbling in the dark will never produce answers relative to any modification involving the electrical signal, so would you please point me to the thread you have mentioned.

Thanks, Trevor.

Trevor,
I even posted earlier in this thread :rolleyes: should have really gone back and recapped before i posted.

I think all the info you would want on this is in mychailo's locker.

(http://www.subaru-svx.net/photos/user.php?mbtoloczko|27876)

Looks as though i was wrong, and you seem to be incorrect. There is something serious going on with the maf above a certain level, you can really see it oscillating above a certain load

Myxalplyx

08-18-2007, 08:47 AM

Looks as though i was wrong, and you seem to be incorrect. There is something serious going on with the maf above a certain level, you can really see it oscillating above a certain load

This is why I mentioned what I did previously. Adding a resistor in line to cap the voltage right before that 4.5 voltage point would solve have of the problem. The other half is to measure how lean the car is running and compensate with adding fuel (A FPR, RRFPR, SAFC, bigger injectors, etc).

No need to get extra tubing to let more air around the maf sensor. Let all the air you want go through it but compensate for the leaner air/fuel ratios.

Bah, it's just talk. I'd love to test this out.

Phast SVX

08-18-2007, 09:15 AM

This is why I mentioned what I did previously. Adding a resistor in line to cap the voltage right before that 4.5 voltage point would solve have of the problem. The other half is to measure how lean the car is running and compensate with adding fuel (A FPR, RRFPR, SAFC, bigger injectors, etc).

No need to get extra tubing to let more air around the maf sensor. Let all the air you want go through it but compensate for the leaner air/fuel ratios.

Bah, it's just talk. I'd love to test this out.

you would need an adjustable rate fuel pressure regulator. You are running a stronger vacuum than stock. A rising rate regulator addx x psi of fuel pressure for every 1 lbs of boost and only works on a pressurized system. Te adjustable rate you can increase overall pressure in the system. Capping the system may not help, would just have to see how it reacts to reaching the threshold of 4.5v, it may still oscillate.. Think of it this way; The sensor is going through the motions, you are merely capping what it sends out to the ecu. This is why increasing the larger ID tubing is a better and often used solution.

oh and whoops, Trevor, I meant u were correct. I should really start paying more attention

XT6Wagon

08-18-2007, 02:53 PM

As i said, this works much better on a hot-foil sensor, and a little R&D would do the trick. The straightline relationship was for ease of discussion...... Going the MAF translator route is pointless, these injectors are not worth the trouble, far too small.

Regarding the RRFPR....

with stock SVX injectors its not a good option. The ~272cc injectors do not perform well over 75% DC, as with any side feed setup.

I used a Vortech RR when running 3.5lbs of boost for a while. I assume you meant an Adjustable rate fuel pressure regulator, since you are saying 1:1, meaning no pressure rise?
http://www.subaru-svx.net/photos/files/Phast_SVX/35676.jpg
i used anywhere from 7-12:1 discs while tuning. from a roll the RRFPR is horrid, dropping under 10:1 (my wide-band was reading in the 10's but as we all know a Bosch is not good for reading much under 10.5:1) accurately in the lower RPM range, to keep fuel safe up top. It functions decently for drag racing, but just dosn't cut it with the amount of pressure required on our rig.

1:1 rising rate means that if you gain or lose 1psi of pressure on the manifold pressure signal then the fuel pressure will rise or lower by 1psi. And yes the ones I use are adjustible, but I've never seen one that wasn't that you would want to buy. Talking about an aeromotive or other one that is designed to be connected in the return fuel line, not attached to the back of the OEM fuel rail.

I've also never encountered a fuel injector that had issues past 75% duty cycle. I'm wondering if its not an issue with the injector drivers as thats honestly the item that gets hit the hardest with high duty cycles. At 100% duty cycle the injector basicly has a free ride as it goes full open and is continualy cooled by fuel. The driver though has it rough as it handling alot of power with no interuption.

Also on the subject, possibly its time to inspect/test/replace the wires for the injectors. I know of newer cars that have corrosion issues with thier injector wiring. Given that atleast my SVX is hardly the least corrosion and wiring problem free car I've seen, running new wires for performance applications might be a good performance mod.

On your setup, The reason I don't like running more than 1:1 is the fuel system gets bruatly non-linear, coupled with what is typicly a brutaly non-linear MAF curve, and you now have fueling issues as the two are basicly out of your control. While I don't advise it, with a good highpressure Walbro fuel pump, 100psi at the rail is possible and makes for a hell of alot of headroom over the stock injectors at stock fuel pressure. Problem gets to be pulling down the maf signal at idle and low rpm since thats going to be about 70psi static at idle for a 20psi peak boost setup (-10psi vac idle => 20psi on boost). So yes, I'd advise larger injectors for forced induction SVX's. Problem gets to be with cars like the STi where idiots put in 850cc/min injectors to replace the 470/480 cc/min stock injectors thinking that the stock ECU running them 100% on boost is bad. So they end up with huge drivablity issues as the 850's are complete crap and a tuning nightmare. Where as a FPR is good for tossing on an easy to tune 10% more fuel if you are paranoid, or have a one in a hundred car that actualy needs more injector on the stock turbo. The STi also is apparently designed for this as I've seen alot of cars rack up alot of miles running 100% injectors with safe A/F ratios.

So moderation in your injector choice is a good idea too. Good news is that the selection of nissan sidefeed injectors is good and those injectors are not the complete pile that is the 850cc/min injectors the STi people love.

Trevor

08-19-2007, 06:28 AM

The problem relative to cold idle surely involves the auxiliary air control valve. This normally opens when the engine is cold and the throttles are closed, so as to override control via the ECU. At start up from cold the mixture is therefore fixed by aperture values, prior to a heating period arranged as correct for the original set up.

When open the AACV valve bypasses the shut throttles, and in so doing notably draws the require air via the MAF. The fitting of a bypass means that at cold idle, the AACV valve will not draw all air supplied to the engine via the MAF, as would normally be the situation at idle with the throttles shut. As a result any signal from the MAF at cold idle, will be distorted accordingly

The MAF voltage spikes and swings in AFR at cold idle which have been noted with a bypass tube in place, could well represent a resultant feedback oscillating cycle. When the running temperature becomes normal, the AACV shuts, the ECU takes complete control of the AFR at idle via the bypass solenoid valve, and all is well as has been recorded.

In the event that a MAF bypass arrangement is used, this should be closed when the throttles are shut, so that the original idle system remains preserved. It is interesting that Greg touched on this issue way back in this rather confused thread, but his idea was discounted.

He also mentioned the idea of shutting off the bypass in line with closed throttles. This could be arranged mechanically, using a throttle assembly from a small engine ex lawnmower, or what have you. A suitable cam and lever arrangement would provide a quick opening at the initial movement of the main throttles. Alternatively this arrangement could be extended to provide control throughout the range of throttle opening, as a means of overall compensation.

It has been agreed that as is obvious, the addition of a bypass introduces extra non metered air, post MAF and prior to the AACV input, which must upset the original parameters. The difficulty, again obvious, is that this aberration must be corrected. I can not see how adjustments in respect of the routing, shape, or dimensions of a bypass tube, can in any way assist in this regard.

I still contend that shielding the MAF element is a well worth trying, as this would be much less complicated than a bypass system in several critical areas. What is latter advice within the thread, confirming the affect of element position within the MAF, tends to give credence to my suggestion.

The maximum output voltage delivered by the MAF can be cheaply controlled by means of voltage regulator IC as I have previously suggested. However if the ratio of air flow to sensor signal can be modified, this should result in a clean signal from the MAF and negate this requirement.

Inserted edit P.S. It has been suggested that a resistor could be inserted in the signal circuit, but this would reduce the voltage throughout the range of operation. Critically the affect would be most severe at the low voltage end and in reverse of requirements.

A resistor in parallel, i.e. inserted across the MAF output as a bleed, would modify the signal such that, as voltage increased there would be an increased reduction in voltage. Just how the resulting output curve would stack up is anybody's guess, but experimenting would not be difficult.

As there are no figures available covering signal current, as a precaution, it would be wise to commence with an overly high resistance of say 250 ohms, no responsibility accepted. A prior current measurement would be wise to enable calculations. A potentiometer/rheostat would present a hazard as it could be inadvertently set too low, but once a safe minimum value was established, a fixed resistor could be included as a safety stop during experiments.

In any event, I hope the above may serve as a summary, so as to tidy up salient points to date randomly included within what has now become a rather convoluted thread.

Myxalplyx

08-20-2007, 08:00 PM

Trevor

08-21-2007, 02:05 AM

Remind me again......

Why is it that the maf sensor is significant if you can push as much airflow through it as you want and add the amount of fuel needed by measuring your O2 sensor (or Wideband O2 sensor)?

I mean, if you can add the necessary fuel needed by measuring your exhaust O2 readings (Or EGTs which are my preference with O2 readings), you really would not have much to worry about. As long as the ECU isn't pulling timing based on the erratic readings. An Apex ITC could be used possibly but that is for another discussion.

OK...I'm scrolling back to read some more. Must've missed something.

The O2 reading is taken after the opportunity for adjustment has passed. The opportunity to adjust has long gone.

The requirement to adjust, must be ascertained in advance of the opportunity to adjust. Hence the MAF at the intake.

Time is waits for no one. :rolleyes: :)

ItsPeteReally

08-21-2007, 04:00 AM

The O2 reading is taken after the opportunity for adjustment has passed. The opportunity to adjust has long gone.
Is this the right room for a five-minute argument?;)

I don't want to seem to be teaching someone who knows all about negative feedback how to suck eggs, but that is exactly what the O2 sensors are there for - to correct for errors in air/fuel ratio estimates generated from the MAF output. The narrowband O2 sensor (more properly, in my estimation, called the lamda 'λ' sensor) detects any deviations from the stoichiometrically correct air/fuel ratio and feeds back the error signal to the ECU. Because of the limited transient response of the λ sensor and the shape of its transfer function the air/fuel ratio continually oscillates around the correct value.

The problems start when the input airflow drives the MAF beyond its measurement range.

The first problem encountered is that there are no longer any correct fuelling values in the ECU's look-up tables. The error feedback from the λ sensors then signal a weak mixture and 'encourage' the ECU to deliver more fuel, but sooner or later the ECU will be unable to increase the injector duty cycle timings any further.

And this is only the first of the problems:eek:

If the only constraint upon arriving at a workable solution is maintaining the correct air/fuel ratio then, as long as we have access to the λ sensor output and a way of feeding that output as a control signal to an ECU, we do not need to know how much air the engine is consuming.

Trevor

08-21-2007, 05:47 AM

Is this the right room for a five-minute argument?;)

I don't want to seem to be teaching someone who knows all about negative feedback how to suck eggs, but that is exactly what the O2 sensors are there for - to correct for errors in air/fuel ratio estimates generated from the MAF output. The narrowband O2 sensor (more properly, in my estimation, called the lamda '?' sensor) detects any deviations from the stoichiometrically correct air/fuel ratio and feeds back the error signal to the ECU. Because of the limited transient response of the ? sensor and the shape of its transfer function the air/fuel ratio continually oscillates around the correct value.

The problems start when the input airflow drives the MAF beyond its measurement range.

The first problem encountered is that there are no longer any correct fuelling values in the ECU's look-up tables. The error feedback from the ? sensors then signal a weak mixture and 'encourage' the ECU to deliver more fuel, but sooner or later the ECU will be unable to increase the injector duty cycle timings any further.

And this is only the first of the problems:eek:

If the only constraint upon arriving at a workable solution is maintaining the correct air/fuel ratio then, as long as we have access to the ? sensor output and a way of feeding that output as a control signal to an ECU, we do not need to know how much air the engine is consuming.

In five minutes you are teaching me nothing. ;) Practical feed back loops are bread and butter within the field of industrial control engineering. :)

A feedback loop is a corrective circuit not a means of control. As you say that is what they are there for and the affect is a continual oscillation as you put it. A feedback loop can not be successfully used as means of correcting an inbuilt error signal, as the “oscillation” will override the designed parameters.

What you are suggesting is that the feedback loop should be used as a way of correcting what would be an abnormal condition. Modifying the the feed back loop in order to correct an inherent anomaly, is putting the cart before the horse, or an ambulance at the bottom of the cliff. Certainly not good engineering and in any event not a feasible option.

You correctly define the problem ---”The problems start when the input airflow drives the MAF beyond its measurement range.” ---The correct approach is to correct this, the first and a major error in the chain.

You state:- “If the only constraint upon arriving at a workable solution is maintaining the correct air/fuel ratio then, as long as we have access to the ? sensor output and a way of feeding that output as a control signal to an ECU, we do not need to know how much air the engine is consuming.”

The measurement of airflow is paramount in the management of any internal combustion engine. You are discounting throttle control, which is the deciding instruction commencing the process. A massive variant is involved, which can not be accounted for by any loop back from an output measurement, even if time were not a constraint.

Consider the train of control without air flow sensing as you suggest. Throttle opened/closed, the engine responds, the changed result is measured after time has elapsed, running adjustments are made based on after affect, the engine then responds. The resulting feedback cycle would surely be interesting/destructive. :eek:

ItsPeteReally

08-21-2007, 10:13 AM

In five minutes you are teaching me nothing.
Is that my problem or your problem?

Myxalplyx

08-21-2007, 10:40 AM

The reason why I stated what I did is because I have done this before. On my Outback Sport, I ran 5psi of turbo boost along with a 60hp shot of nitrous. The only thing I relied upon religiously was the O2 in the exhaust and even more than that, my Exhaust Gas Temperature (EGT). The car ran fine without issues at all.....at WOT. I left all non-WOT measurements for the ECU to take control over. Only at WOT did I take control of my air/fuel ratios by adding or taking away fuel. My point of reference was where the EGTs were when I ran the car stock. That is what I 'shot' for while tuning. As stone age as that may sound, I never had a problem between 59k and 110k (when I removed the turbo and nitrous). I did not know how to 'tune' so that is what I did and it worked.

So my point is, despite what the MAF says, why not take control of your air/fuel ratios by keeping the EGT at stock temps by controlling the fuel and timing yourself? Take moderate steps if boosting (Like 1psi, tune at WOT, repeat at 2psi). This should be able to work unless I am missing something.

Trevor

08-22-2007, 03:20 PM

Is that my problem or your problem?

The sarcasm is noted. Obviously the wink ;) I included, sa as to represent a sense of humour, was beyond your comprehension. :p

Myxalplyx

08-22-2007, 04:45 PM

The sarcasm is noted. Obviously the wink ;) I included, sa as to represent a sense of humour, was beyond your comprehension. :p

I'm still confused. You stuck your tongue out at the end of that one. Are you still joking? :D :ninja:

Trevor

08-22-2007, 10:22 PM

I'm still confused. You stuck your tongue out at the end of that one. Are you still joking? :D :ninja:

As a result of your unexpected reply so am I. :confused: :) Ask the addressee --- ItsPeteReally. :lol:

ItsPeteReally

08-23-2007, 06:02 AM

On the whole, I’d rather people thought for themselves. I like to think that most people are capable of that.

Consider the humble MAF in its box, sitting next to hundreds of other MAFs in their boxes.
Are they all the same?
What do you think?

Well they are all obviously pretty similar, but they are probably not laboratory standard. Let us hope that someone in the manufacturing plant samples at least a few percent of them so that we may have some degree of confidence that they are not too wildly out.

Let us try and retain a degree of confidence that the MAF gives us some indication, within a few percent, that a certain quantity of air is passing, because we can measure the cooling effect that the air has on a heated surface.
We can convince ourselves that despite the pulsations and turbulence of the airflow, we have positioned the MAF so well that we can conveniently forget about such problems.

We have done some elementary physics and believe that, providing we know the air temperature and the barometric pressure, we can pretty much translate that information into knowing the mass of air, and consequently derive the mass of oxygen.

But wait a minute, how accurately does the ECU know about the variations in air temperature and barometric pressure?
Actually, wait even longer, shouldn’t there be a factor for air humidity in this calculation too, doesn’t that have a bearing on the cooling abilities of the air?

Ask yourself how much faith you now have about the knowing the mass of oxygen entering the engine.

Ask yourself how much faith you have that equal quantities of oxygen enter through the intake valves of each bank of cylinders, in any position of the IRIS valve.

We won’t even try to wonder whether equal amounts of oxygen pass each inlet valve in each bank of cylinders.

Well, now we know how much oxygen is entering each cylinder, don’t we?

Let us consider how accurately we can inject a known mass of fuel into the combustion chamber to be burnt by this mass of oxygen.

We could try and go through the same process, trying to figure out how accurately we can measure the fuel.

It starts to get very difficult, as we don’t even know what the fuel’s chemical composition is, (how much carbon, how much hydrogen for a start), we have no idea what its viscosity is and how it flows, and we don’t even attempt to measure what its temperature is, so we have no idea about how its volume relates to its mass.

The ECU simply attempts to pulse the injector for a certain amount of time, and thereby deliver a not very certain volume of fuel. How much oxygen that amount of fuel actually requires for complete combustion is largely open to conjecture.

It appears that we have gone through a lot of time and trouble to get something that could probably be done just as well, perhaps better, by the humble S.U. carburettor (at least you can actually adjust the S.U. carburettor!).

Using such an air/fuel management system the engine will run, but all of the air/fuel ratio mappings have to err on the side of caution to preserve the health of the combustion chambers.

But, consider what happens when you close the feedback loop by knowing just how well the combustion process has been carried out.

It turns out that the application of negative feedback, via the lambda 'λ' sensor, turns this flawed control and measurement system into a thing that might just work.

The lambda 'λ' sensor continually sends too weak/ too rich error correction messages to the ECU, which adjusts the fuelling. Not only that, but there is a sensor for each bank of cylinders!

It’s the feedback that makes the system work properly.

In my earlier posting I alluded to the saying that “You shouldn’t try to teach your grandmother how to suck eggs”.

An interesting phrase, what does it mean?

Does it mean that your grandmother has so much knowledge and experience about the craft of egg sucking that only a fool would believe that he knew anything that could contribute to her skills?

Or does it mean that she is so inflexible and sure that she must be right that she will never listen to you?

I leave the answer up to you.

Because my understanding of the matter could very easily be wrong.

Phast SVX

08-23-2007, 11:58 AM

Pete,

Thats all in good. You do realize that the oxygen sensors in our system are not 5 volt lamdba sensors, and our ECU is not a wideband EUGO controller/decoder?

The basic Oxygen sensors in our system output a voltage based on the amount of oxygen present to indicate a "rich" or "lean" condition, not by means of RBT or LBT, but by means of stoichiometry (14.7 parts air to 1 part fuel). This type of sensor is only, yes i repeat only, utilizied by the ECU in closed loop, or partial to low throttle cruising conditions where 14.7:1 is an optimal operating range. This is what the feedback loop 02 approach is designed for in our system, but open loop, high load conditions switch to the load/volume based maps that we are takling about altering.

A lambda sensor can be utilized well by many aftermarket ECU's, that will tune on the fly. That coupled with EGT's and you can tune to near perfection and safety. I have a sensor in my car, and monitor all the time while driving. I do not run it in "Lamda" values, a .00-1.00 system that willi give you true output values, unless I am running Ethanol E85.

Myxalplyx

08-23-2007, 12:59 PM

In my earlier posting I alluded to the saying that “You shouldn’t try to teach your grandmother how to suck eggs”.

An interesting phrase, what does it mean?

Does it mean that your grandmother has so much knowledge and experience about the craft of egg sucking that only a fool would believe that he knew anything that could contribute to her skills?

Or does it mean that she is so inflexible and sure that she must be right that she will never listen to you?

I leave the answer up to you.

Because my understanding of the matter could very easily be wrong.

http://www.worldwidewords.org/qa/qa-tea1.htm
"don’t give needless assistance or presume to offer advice to an expert"

Too many experts on this board for me. I bow down!! :WTF:

Trevor

08-23-2007, 09:52 PM

On the whole, I’d rather people thought for themselves. I like to think that most people are capable of that.

Agreed. :cool:

Your verbose and rather patronising lecture, indirectly indicates that you have now grasped the reason for, as well as the exact function of a feedback loop. What is more important, that a feed back loop does not, and can not form a function of control, as was your earlier suggestion. ;)

ItsPeteReally

08-24-2007, 12:29 AM

What is more important, that a feed back loop does not, and can not form a function of control, as was your earlier suggestion. ;)

Maybe it's me, perhaps I've got it all wrong.
Convince me.
Pick a simple feedback system and show me why output measurement and feedback does not form the essential part of the control system. In fact you go further than that, you say it cannot perform a function of control.

Perhaps we could consider the ballcock in a cistern.
Or the pendulum and escapement in a simple mechanical clock.
Or the thermostat in a domestic oven.
Or you can pick your own example.

Educate me. I'm not too old to learn, and I'd like to think that I'm not too stupid to learn either.

Trevor

08-24-2007, 02:19 AM

Maybe it's me, perhaps I've got it all wrong.
Convince me.
Pick a simple feedback system and show me why output measurement and feedback does not form the essential part of the control system. In fact you go further than that, you say it cannot perform a function of control.

Perhaps we could consider the ballcock in a cistern.
Or the pendulum and escapement in a simple mechanical clock.
Or the thermostat in a domestic oven.
Or you can pick your own example.

Educate me. I'm not too old to learn, and I'd like to think that I'm not too stupid to learn either.

Carefully read again my words as below, exactly understand their meaning, do not add any suffix and be convinced. :rolleyes:

“a feed back loop does not, and can not form a function of control,”

N.B. “a function of CONTROL” not “of the/a control System".

From the dictionary within my computer:-

control
noun
1 the power to influence or direct people's behaviour or the course of events : the whole operation is under the control of a production manager | the situation was slipping out of her control.
• the ability to manage a machine or other moving object : he lost control of his car | improve your ball control.

Your original theory was that altering the feedback signal could directly alter an instruction originated and dictated by the MAF . This is not possible. The loop can only have an affect AFTER control has been set and the result is displayed and measured, whereupon recurring adjustments are put in train. The basic instruction from the MAF remains valid and is not altered.

I quote and comment on your suggestions of similarity:-

“Perhaps we could consider the ballcock in a cistern.” ---

The position of the float controls the inlet of water and fixes the level and there is no form of ongoing adjustment in respect of original setting which remains fixed.

“Or the pendulum and escapement in a simple mechanical clock”

Fixes the speed of the movement as per set parameters, but makes no ongoing adjustment. High class clocks incorporate mechanical thermal components for this duty.

"Or the thermostat in a domestic oven."

Again the operation of a thermostat does involve feedback but the desired temperature i.e. control is fixed via the setting. The thermostat functions maintain the set parameters but can not correct an error resulting from an incorrect setting. The manually operated dial correlates with the MAF in any form of comparison.

My example:-

Automatic audio volume control, AVC as has been incorporated for many years within every domestic radio. Here the volume control is the controlling component (Think MAF). An electronic loop adjusts amplifier gain in spite of variations in the input signal, by taking/using measurement post volume control. N.B. There is no control or influence in respect of the original set parameters.

QED. :D

Phast SVX

08-24-2007, 04:19 PM

Wow

12345

ItsPeteReally

08-25-2007, 01:43 AM

Wow

Very succinctly put sir.

He was right about the ballcock, but missed the fact that the feedback from its position was the only 'function of control', whatever that means. There is no attempt to measure and act upon the either the input water pressure or the output water flow.

Similarly with the pendulum, which works solely as a feedback mechanism. Without it, the hands would rotate at a speed related to how tightly the mainspring was wound up. Once again the pendulum is the sole 'function of control'.

Lastly he seems to think that the oven thermostat is an input control sensor, like the MAF, rather than an output measurement sensor, like the O2 sensor!

The oven has no idea of how much energy is being fed in, what the thermal load is inside the oven, or what the external air temperature is, all it knows is the feedback from the internal temperature sensor, and uses that to control the input energy source. The oven has no MAF equivalent, it doesn’t need one!

Finally he mentions the AVC (more properly called AGC) in a domestic radio. Not only does it not act as he said it does; if it did pianissimo sections would be as loud as fortissimo sections, flattening the dynamic range of the music, but also, it doesn’t work as he describes either.

What it actually does is attempt to keep the amplitude of the carrier wave constant so that powerful nearby radio stations are as subjectively as loud as distant weaker radio stations. All of this control is achieved by feeding back the rectified carrier wave voltage, which is extracted before the volume control, to control the gain of the radio-frequency stages. The volume control plays no part in this process at all, and certainly is not ‘the controlling component’. The AGC system is totally unaware of the volume control setting.

Trevor

08-25-2007, 08:45 AM

Pete, damn it man, read understand and digest what you read. Having done that write accurately when you reply. Or is it that a ploy whereby you hope that ever increasing confusion will conceal your errors?

It is interesting that you are not willing to face the music and slyly reply by way of back handed sarcastic remarks directed towards a third party.

You show that you are unable to grasp that the set point (the correct term within control engineering), can be either fixed or adjustable. Setting this point is the control function. Any following feed back loop does no more than adjust subsequent variables in order to maintain the set point. It can not and dues not alter the set point. It does not control, it is confined to making adjustments after the method of control has set the required functions/level, whatever.

In respect of a ball cock the controlled parameter (set point) is confined to the level of water. Control here is reliant on adjusting the position of the float. Move same and you control the water level. Why in hell are you referring to water pressure or flow? Trying to shuffle sideways?

Now we have a pendulum. Previously we had a very strange clock which in your words comprised, “pendulum and escapement in a simple mechanical clock.” Some clock ! now on the scene is a new type of pendulum --- “which works solely as a feedback mechanism”.

A mechanical clock can be and is controlled via readily available adjustments. The degree of control is limited as the clock is designed accordingly. The pendulum weight can be moved up or down. The spring within an escapement in effect lengthened or shortened by means ot a lever. This is how the mechanism is controlled.

Once the controls have been set, i.e. the set point established, the pendulum simply acts as a simple governor NOT as a feed back loop. Check on the governor within a clockwork toy. In a clock, what could be misconstrued as a feedback loop, is the mechanical system catering for changes in temperature. Even here there is no feedback and the parameters are predetermined and set.

As for the oven. The knob on the thermostat is the means of control. The feedback function only maintains the set point and is not a means of control. What the thermostat “knows” and is required to “know” as you put it, is the position of the knob, i.e. the controlling parameter (set point) as adjusted/set by the cook.

AVC/AGC Smart ass, in my part of the world it was/is known as automatic volume control. This description having been decided upon so that it could be publicised as a sales gimmick. Here you inject more sarcasm and show that you are unable to read and assimilate. You endeavour to twist my words in an effort to prove an error exists. My words:-

“An electronic loop adjusts amplifier gain in spite of variations in the input signal.”

I was intentionally not specific so as to simplify the description of my example. I WAS IN NO WAY IN ERROR. Your statement is devious and dishonest.

You state:-"Not only does it not act as he said it does; if it did pianissimo sections would be as loud as fortissimo sections, flattening the dynamic range of the music, but also, it doesn’t work as he describes either."

You go on with a lecture by way of showing your perceived abilities. I sucked eggs when the process involved auxiliary plates within a multi purpose vacuum tube.

You imply that I referred to an adjustment within the audio stages. I did not suggest that the adjustment involved is in any way related to, or is intended to cover anything more than very short term fluctuations within the RF input. At no point did I refer to an audio signal. Your attempt to discredit me is stupid, as well as devious.

You do nothing more than argue incorrectly over side issues involving only examples put forward, rather than involve yourself in what is the essence of this thread. Namely that your proposals are not viable.

In respect of the SVX engine management system, manual control is initiated via the throttles. As a result air flow becomes altered due to the engines response. The resulting airflow then initiates overall control of the engine via the MAF.

The MAF senses the engines requirements in respect of air and continually fixes a constantly varying set point accordingly. The MAF is the first point of control, within an integrated automatic system incorporating multi inputs.

If the MAF signals maximum flow when due to modifications, this is not in effect the real situation and all that follows is out of order and in error. Adjustments should be initiated relative to airflow and all parameters setting combustion issues set/varied accordingly by this the first means of control.

Any feedback loop adjusts to maintain set levels as are dictated by the MAF. These adjustments via feedback, involve a delay. Altering the loop must distort the application of control from the MAF. This proposed alteration comprises the essence of my argument whereby I disagree.

Messing with the feedback loop is not an acceptable method of adjusting for errors originating from the MAF, i.e. the first control with in a control system. This proposed arrangement can only result in distortion, and a never ending requirement to compensate for the errors which will occur. Furthermore there are several other related inputs to the ECU which if applied in conjunction with a distorted signal must add an increasing factor of errors.