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

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.

If someone has a spare intake pipe that they want to send me, I can give it a try...

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?

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. :-))

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

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?

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.

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:

This thread is actually worth resurrecting

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

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.

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