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.

Nice
 

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/...547#post365547

Thanks for the info.

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! :)

new bypass tube...
 

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/fil...czko/31158.jpg

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)

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.

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.

I was corrected, according to the FSM's the XT6 fpr is 43.5 psi.

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.

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.

the nature of bypassing the meter will most likely bring a condition like this at some point in the range of function.
phil