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Old 07-28-2009, 12:47 AM   #4 (permalink)
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Join Date: Jun 2008
Location: Northwest Lower Michigan
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Red Car - '89 Chevrolet Celebrity CL 4 door
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90 day: 36.47 mpg (US)

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Originally Posted by hyperyaris View Post
A more free flowing exhaust gives better power but less fuel effieicney, and vice versa. You could block up your exhaust lol.
Is that necessarily true? What I have understood is a LARGER exhaust usually hurts FE, since a larger diameter actually slows down the velocity and stagnates the flow at low revs. But keeping the factory size with a more free flowing design (headers, mandrel bent pipe, etc), shouldn't that help FE if anything? Seems like it would be part of reducing pumping losses.

Of course, any gains would be small and not worth the price of buying new parts. But if you need new parts anyway, then maybe.

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