Engine Horsepower/RPM Predictor By Bowling

Dan Bratten suggested a program which would relate engine power and RPM to CFM (cubic feet per minute of air flow). I developed the following: Enter the maximum flow values at a given test pressure, engine CID and number of cylinders, and the program will compute maximum engine horsepower and the RPM which this maximum occurs. The test pressure can be entered in inches of mercury or inches of water, the latter a common unit used on head flow benches.

User Inputs:

Maximum Flow CFM For One Cylinder (Intake):

Test Pressure for CFM Measurement:

Units For Test Pressure:

Engine CID:

Number Of Cylinders:

Press this button to submit a computation:

To reset the form input:


The following equations were used in the above calculation:
cidone = cid/cyl
if units="Inches_Water" then cvt = 10 else cvt = 0.735
cfmcorr = cfm * sqrt(tp / cvt)
hp = 0.43 * cfmcorr * cyl
rpm = 2200.0 * cfmcorr / cid

Bruce Bowling
Bowling Superior