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Old 11-27-2008, 02:52 AM   #24 (permalink)
some_other_dave
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Quote:
Originally Posted by dichotomous View Post
yes, especially for lower rpm torque, make the exhaust bigger.
Hmm?? Are you sure?

From what I have read about naturally-aspirated engines, making the exhaust primaries narrower and longer will help with the low-end torque. Narrower and longer pipes are better at promoting flow velocity, but worse for sheer volume of flow. And long primaries (how long? dunno!) can set up the resonance to better evacuate the chamber at lower RPMs than sort primaries.

There is also the effect of any secondary pipes after the collector for the primaries (if you're doing a 4-2-1 header), and of course that of the pipe after the final collector, but they get less and less important the further out you get from the exhaust valve.

Then again, this is all book-learning. And especially when it comes to fluid dynamics, reality can hold an awful lot of surprises that aren't in books...

-soD
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