Quote:
Originally Posted by MechEngVT
metro, backpressure is bad for engines. The reason that engines don't do better exhausting straight to open atmosphere is that acoustically-tuned exhaust pipes can do *better* to improve performance than zero backpressure. When an exhaust pipe comes into tune with the engine's pulsing the exhaust port will actually see a vacuum near the end of the exhaust valve event that improves scavenging. Having an exhaust pipe to achieve this tuning inherently provides backpressure, but it isn't the backpressure that helps the engine it's the absence of backpressure during certain designed operating parameters that helps the engine.
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very well put, thanks.
I have played with tuned exhaust headers and mufflers on an engine dynomometer... (normally aspirated gas engine) Exhaust theory is not as well understood as some would think (I barely grasp some of it...).
Are you saying that adding a turbine wheel might negate the positive effects of a 'tuned exhaust'? <trying to answer my own question here...> Thinking more, I bet it would. Perhaps a well designed system with turbine wheel could be tuned? i get a little confused since the only exhaust turbine wheel engines I'm familiar with to date, have the turbine mated to a compressor that adds power, a completely different animal than the idea being floated here.