Ok say I had a centrifigal supercharger with a maf attached on the intake of the sc. So I'm tooling along at 5500 rpm w/14 psi boost and get off the gas. The throttle blade snaps closed and the bypass valve pops open to bleed off excess metered air that would instead deadhead at the throttle body. Does the ecm lean out the mixture in this situation? Will it know that all this air is being let out via the tps indicating the butterfly closed? Basically, what happens in a decceleration situation with a maf system?

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter

 

On the Mass Air Mustang that I helped install an ATI, the blow off valve is before the mass air.

 

ATI superchargers for F-bodies have the MAF on the outlet side. There's a big debate between draw-through, and blow-through MAF set-ups on forced induction. I could go on about the pro's and con's of both, but I'll save the trouble.

[This message has been edited by MJT (edited December 25, 2000).]

 

Please share your info with us. I for one would like to know what the pros and cons are. Thanks.

Willie

 

82z, the ECM doesnt know it is being let out. As far as it knows, the MAF has already metered the air, and is injecting fuel to match it. If it leaves via a bypass valve, then it is going to richen up a lot. I had a problem with this on my car so took the valve off. To get it to run correctly, you must take the air that is vented from the valve and have it ducted back into the intake tract before the compressor, but after the MAF. This way, the air is still in the system.

 

I see you could run the outlet of the blowoff valve to just behind the outlet of the maf. The compressor would just not draw as much air through the maf. This is assuming the maf is upstream of the compressor. I understand now

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter

 

Sorry for the delay on the reply. Some of the problems associated with a draw-through MAF are:

-Decreased throttle response due to the MAF being located further from the intake.
-Air metering problems due to the bends necessary to mount the MAF on the inlet side. It's not as much of a problem on F-bodies because of the hot-wire positioning/function(bigger problem on Mustangs)
Blow-through Cons:
-Able to reach max. 255gm/sec flow at much lower speeds. A problem only associated with stock MAFS/stock values
-Positive manifold pressure can trick the MAF sometimes at part throttle. Know this first hand.

Of course, as with any engine combination, sometimes you don't run into any of these problems with a proper tune, luck, and what not. So far, I do know that the blow through is a big negative factor with forced induction. You have to program a high A/F ratio after max flow to trick the computer into making the ideal A/F ratio because of the unseen, increased air flow.

 

I used to run a Paxton which relocates the MAF to the intake side of the compressor (draw-through). I attained peak MAF reading of 255 g/s at ~3,000 rpm's when in boost. Mind you, this is a 305. I will be installing an ATI system which uses a blow-thru design. So what kind of MAF readings should I expect? Any different than what I used to see with the draw-through Paxton?

Then why not just relocate the MAF to the compressor intake side?

Willie

 

Yes, you'll peak at about the same RPM's. On my brother's 377, D-1, it peaks closer to 2500 RPM's, lol. There's a few reasons not to put it on the intake side. The D-1 has a 4" intake, there's hardly enough room for the elbow and air filter already, and any cold-air type intake is out of the question because of the intercooler ducting.

 

Why not convert to speed density? That is what I have done. Then, you dont even have to worry about it.

I feel that in the long run, its more effective, and gives you more controllability over your A/F and timing curves.

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-86 IROC
Vortech stuffed EFI 406 in progress
-=ICON Motorsports=-