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midlife midlife is offline
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Join Date: Apr 2004
Location: Central CA
Posts: 568
I am interested in the blow through vs suck through argument, because I am planning on turboing my 3.2.

Here is my thoughts on this:

The AFM measures flow, not mass flow. It does not know the pressure of the air. On a blow through, say you were at 1 bar of boost, there would be roughly twice as much air going through for the same AFM reading. This is OK because the rising rate regulator is also increasing fuel flow proportionally to boost. I would think you would need a different chip for a suck through.

Arguments against suck through:

On stock NA engines, I believe the AFM maxes out at high RPM. With a suck through boosted application the increase air flow would cause the AFM to max out at even lower RPM's, and you will lose all part throttle air/fuel ratio controll. You would need an AFM with a greater range.

Also a turbocharger is more sensative to pressure drop on the suction side.

Just my .02
'69 911 Targa w/ 3.2
Old 01-26-2009, 12:19 PM
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