Megasquirt Advice and discussion.

RotaryProphet · 12-10-2009, 11:41 AM

15psi is always 15psi, but 15psi at 80 degrees is not the same as 15psi at 160 degrees; this being what compressor efficiency is measuring (heat added to the intake charge). A larger compressor will generally have better efficiency numbers higher up in the airflow range, and a wider efficiency island.

You aren't changing the "flow", persay. Given a certain engine condition with a better compressor, you're flowing the exact same volume of air (assuming you have the exact same pressure), but the better compressor will be pushing a cooler, and thus denser air charge. (Which would be mass, as opposed to volume).

This is why a MAP based system also requires an intake air temp sensor to correctly calculate the air density. A MAF system measures mass directly, and is probably more accurate under a wider range fo circumstances, but the restriction to inlet flow leads me to use a MAP/IAT system 90% of the time. I would choose a MAF for things like hill-climb motors where rapid changes in altitude would necessitate the wider operating range, and self barometric correction would be more desirable.

12-10-2009, 11:41 AM	#26
RotaryProphet Rotary Fanatic Join Date: Sep 2008 Posts: 147 Rep Power: 17	15psi is always 15psi, but 15psi at 80 degrees is not the same as 15psi at 160 degrees; this being what compressor efficiency is measuring (heat added to the intake charge). A larger compressor will generally have better efficiency numbers higher up in the airflow range, and a wider efficiency island. You aren't changing the "flow", persay. Given a certain engine condition with a better compressor, you're flowing the exact same volume of air (assuming you have the exact same pressure), but the better compressor will be pushing a cooler, and thus denser air charge. (Which would be mass, as opposed to volume). This is why a MAP based system also requires an intake air temp sensor to correctly calculate the air density. A MAF system measures mass directly, and is probably more accurate under a wider range fo circumstances, but the restriction to inlet flow leads me to use a MAP/IAT system 90% of the time. I would choose a MAF for things like hill-climb motors where rapid changes in altitude would necessitate the wider operating range, and self barometric correction would be more desirable.