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SignUp Now!Originally posted by PCS74
It can be beneficial to think of the forced induction engine as a naturally aspirated engine operating in a high pressure environment.
I think you meant the >, instead of the <, although it is close to correct as it is written. The intake pressure is almost always less than the exhaust under boost, giving a value of intake/exhaust of less than one. It is POSSIBLE, on highly tuned race engines like Formula 1, to get close to or, greater than 1, but in most street applications, the number will be close to 1/2. Since the exhaust pressure during boost periods will be significantly higher than the intake, the exhaust valve in a turbo engine should close pretty soon after TDC, and there is little/no possibility of using exhaust tuning to "pull" spent gasses from the combustion chamber. (Even on a normally aspirated engine, tuning headers for a 90 degree V6 is tricky) Some of the features used on NA headers should work well on our cars, though, like the "anti-reversion" design used by one of the big header vendors. And smooth transitions, gradual bends, etc, to get the flow to the turbine without losing energy or unnecessarily increasing backpressure are good, too. But it's hard to put a number on these, since there are few if any dyno tests. Just seems like there are better ways to spend a buck.Over-scavenging is highly unlikely on the Buick, but turbocharged vehicles can achieve intake/exhaust pressure ratios <1.
Originally posted by PCS74
The turbocharger does not negate the need for efficient exhaust scavenging, it increases it.