I was looking at pictures of the PFIspeed turbo setup and noticed that the MAF sensor is just downstream from the turbo, meaning it will sense hot, boosted air coming from the turbocharger before being cooled by the intercooler. Air leaving the intercooler will be cooler and therefore denser. To me it makes sense to have the MAF sensor located as close to the intake as possible so that the measured air flow is accurate. On the other hand, hot air leaving the turbo is also moving at a higher velocity than cooler air leaving the intercooler, so maybe there is no inaccuracy involved.

Any thoughts?

(Oh, by the way, I did my homework and read the entire 440+ post 4th Gen Turbo thread, and I also did a search and found nothing on this.)

 

if I remember correctly fomr the pics the MAF on the PFI kit is mounted in the stock position on the cool side of the charge after the IC(very similar to the Stillen SC setup...so its getting cool air, not hot air....I'm pretty sure thats how it looked when I saw the pics a few months ago. on my friends turbo 92GXE he has the MAF on the intake side, so it reads the air entering the system, rather than the charged/pressurized air...

 

The MAF is before the turbo, ala Stillen V2 Supercharger.

 

This has also puzzled me. If the air is being metered before coming into the system wouldnt it be way off? Particularly when you have a blow off valve.

 

ahhh yeah just loked thorugh the Turbo thread, now I see...I got one of the pipe couplers confused with the MAF.

 

Oooops. You're right, it is. My bad.

 

Yes, you will run slightly rich while the BOV goes off. This can lead to rough idling or stalling problems.

 

I think you can use a recirculation style BOV(no atmospheirc relase, but release back into the intake path) in that case...thus when the BOV goes off the "cycle" isn't broken so to speak

 

Would it not be best to have the MAF as close to the throttle body as possible, though? Why do the Stillen V2 and PFI turbo setups have the MAF before the blower? It can't be for convenience, because there is plenty of space for a MAF in the piping going into the throttle body.

I would think the difference in the amount of air entering the intake manifold vs what the MAF is sensing whenever the butterfly valve is opened quickly would be quite significant, due to the compressibility and inertia of the air column in the long piping tract, momentarily resulting in a very lean mixture.

 

Are you talking before or after the turbo? If before, the MAF still measured the charged air so it's still not going to work that well since you can't compress it back to the charged piping (I hope it makes sense). If it's after the turbo, just don't use a BOV... but you'll get compressor surge.


That's because the MAF tube is plastic and will break/leak with a nice amount of pressure.

Rich mixture... since the ECU is injecting more fuel to compensate for the extra air.

 

Okay, plastic tube plus pressure equals nono. That makes sense, although the Stillen V1 kits had the MAF after the blower. Any history of problems?

I would think that the surge of air would be lean, not rich, since it takes a while for the MAF to register that the air flow into the engine has increased if the MAF is at the beginning of the intake piping tract. Maybe there's not enough of a lag to make much difference?

 

I guess I'm talking about after the MAF on the charge side into the TB...throttle plates close, BOV opens, MAF senses an airleak sort of(I guess)...all types of nice **** happens! thats why I always thought the best was around this was to use a recirc BOV to send the air back to the intake/turbo piping, thus you get no break in the cycle....was that clear

 

MAF upstream of turbo...