CFM Question
04-30-2004, 02:27 AM
#1
2nd Gear
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CFM Question
Hey guys,
I was just trying to figure out how much air our n/a engines flowed. I used the (cubic inches*rpm)/3464. And this gave me somewhere in the neighborhood of 270 cfm. This I'm assuming is ideal, and hence not that close to the actual air flowed. Anyone have a better idea of what the real cfm flow is? And does anyone know what the rev limiter is set for on an 85.5 - is it 6200 or 6400? Thanks for your time!
I was just trying to figure out how much air our n/a engines flowed. I used the (cubic inches*rpm)/3464. And this gave me somewhere in the neighborhood of 270 cfm. This I'm assuming is ideal, and hence not that close to the actual air flowed. Anyone have a better idea of what the real cfm flow is? And does anyone know what the rev limiter is set for on an 85.5 - is it 6200 or 6400? Thanks for your time!
04-30-2004, 01:33 PM
#2
Three Wheelin'
It depends on the volumetric efficiency at the horsepower peak rpm. The US version of the 944NA has its horsepower peak at 5500 rpm, and a VE of about 80% at that rpm. This would give an airflow of about 195 cfm. The 85.5s may have a revised cam profile that raised the peak rpm a bit and/or increased the VE a bit.
The rev limiter is set at 6,480 rpm.
The rev limiter is set at 6,480 rpm.
05-01-2004, 03:52 AM
#3
Race Director
Typical conversion requires knowing the VE at each RPM. Most efficient is VE=1 at the torque-peak. All other RPMs flow less air than the theoretical maximu. General rule of thumb is that max CFM = 1.6*HP. So you take HP at the torque-peak, about 125bhp. So 125bhp * 1.6 = 200CFM max.