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Old 09-06-2007, 08:42 PM   #12
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Member#: 882
Join Date: Feb 2000
Location: Michigan
2004 WRX Wagon
very blue


Originally Posted by jvb6806 View Post
what variable do i need to add to that equation to be able to read that map correctly?
Compressor map is in standard mass flow rate (i.e. flow rate at standard atmospheric pressure). As such, the BIG thing you're missing is pressure ratio (manifold pressure over standard atmospheric). You're also missing VE, which will be less than 1.0 and tend to reduce the flow...

Anyhow, from your eq. before:
volume of air (cu ft/min)= (rpm x cid x VE) * (Manifold Pres + 14.7)/14.7
OR (in SI):
flow rate (m^3/s) ~= (RPM * disp * VE) * (MAP/101.7) *(1/120)

disp in m^3
VE in %
MAP in kPa

at 18psi of boost, MAP = 225kPa
m/s = (7000 * 0.002 * 0.85) * (225/101.7) * (1/120) = 0.219, which putts comp. eff off the charts....
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