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Reader Question: Air Flow
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You wrote an article http://www.omninerd.com/2006/07/16/articles/57 Your graph Cold Air intake at 92 ambient. What units is the flow in? I think Im confused also. Shouldnt the flow rate go up with RPM? Have you ever done a map of RPM versus flow rate or have any idea what the exhaust flow rate is at idle? Thanks. Trying to blow myself up!
Actually, the Jeep Wrangler features a MAP sensor as opposed to a MAF sensor. MAP measures manifold air pressure while MAF measures manifold air flow. Soooo – I cannot measure the air flow directly. However, if you look at the provided equations, you can calculate it.
Engine Mass Airflow = RPM * (Air Pressure / Intake Temperature)
Thus, your assessment is correct. With increased RPMs comes a higher air flow. Using the snorkel graph you can see that 5.96 psi * idle RPM (roughly 600) will get you a flow of 3576 compared to 20643 which was derived from 9.83 psi * moving RPM (roughly 2100 at 65mph).
Hope that helps.