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Old 05-22-2010, 02:18 AM   #26 (permalink)
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Originally Posted by COcyclist View Post
So Autoteach, I read the Exhaust Theory 101 and I get the exhaust scavenging concept. But in a turbo car, does this mean that the whirring turbine blades eliminate the pulses at the turbo and therefore from that point on bigger is better, even for ecodriving? A 3" exhaust on a 1.9 TDI could increase mpg at light engine loads?
Sorry it took so long for me to reply...
Pressure waves, for the most part, would be reflected at the turbo and back towards the cylinders. The critical aspect that is occurring before and after the turbo (remember that each vane is a wing, and lift has to do with the pressure difference above and below, along with SA), so less restriction after the turbo will definitely increase turbo pressure and spooling at all rpms. To understand why this is good for all driving, including ecodriving, you need to look at engine efficiency:

By increasing boost, you increase thermal efficiency, or power output, which requires less throttle, and less fuel (see thermal efficiency). Turbo vehicles see gains after the turbo in both low/top end power and mpg.
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