Originally posted by Aussie SVT:
Well I diasagree with your ideas purely due to these facts:
That ECU is CALIBRATED for a certain orifice size in the ECU, i.e for "x" m/s the ECU will inject "y" litres of fuel, and as you may know flowrate, Q=A.v, where A is the cross sectional area, and v is the velocity of the air passing through the cross sectional area measured, at any given point in time. Thus for the point you stated, i.e a fixed volume of air which is dictated by the volume of air induced by the engine per 720° the crank turns (lets assume 100% v.e., therefore 2.5L of air), the velocity will be lower through the large diameter MAF than that of a smaller ID MAF. And therefore the MAF will report a lower velocity to the ECU, which in turn makes the ECU think that less air is entering the engine and thus the ECU REDUCES the amount of fuel injected into the engine for that volume of air, thus increasing the A/F ratio (leaner).
Again, incorrect. What you state would be true IF the MAF sampling tube size were fixed. With a larger MAF size on equal size engines, the larger size MAF will also have a larger sampling tube size, or just smoother flowing sampling tube to send the correct signal. The sampling tube MUST do this to "read" the same volume of slower moving air as the smaller MAF's, faster moving air within the sampling tube. The entire MAF size is not even known by the ECU.
If it were a fixed volume of air at 100%, we wouldn't need a MAF. I know you stated it just to make the math easy, but it also negates your point. One of the main reasons to get a larger MAF is to unrestrict air flow, thereby increasing the volume of air ingested. This is exactly why some people don't see any improvements by changing the MAF as the MAF isn't always the restriction in the air flow.
Anyway, I see your point. You just missed a few variables in there...
