Quote:
Originally Posted by RobertSmalls
I've heard conflicting things over the years. If no ECU modifications are made, will a car get better FE with reduced exhaust backpressure? Is backpressure ever desirable?
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My understanding is that no, it is not. I read an article once about someone who put a butterfly valve into an exhaust pipe and set out to determine what was an optimal amount of back pressure for different engine loads, with the goal of using the butterfly to create the right amount of backpressure. Turns out that no extra backpressure was helpful at any engine load.
Another theory I heard was that an exhaust pipe that is too large in diameter for the application will actually allow atmospheric pressure to work against the engine. I have no idea if this is true or not.