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Old 02-08-2018, 12:14 AM   #21
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Join Date: May 2004
Location: St. Louis

Originally Posted by gsellstr View Post
Think of it this way...40psi of water pressure, you will get a LOT more water from a fire hose than a garden hose.
I'm not quite sure that analogy works completely here, because PSI is just a byproduct of the CFM. Well, the relative difference between how many CFM the turbo is moving and how many CFM the engine is consuming. If the little turbo was really moving less CFM, and the engine relatively the same, then it would result in less HP. The air would 'pile up' less in the intake.

What (I think) happens is that the volumetric efficiency of the engine changes based on the exhaust backpressure. The small turbo makes a lot more back pressure, thus the engine isn't as efficient at cycling air through, so the smaller CFM flow is matched by the reduced efficiency of the engine, resulting in the same PSI. Less air crammed in balanced by less air consumed.
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