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ananthkamath · 14th April 2007, 08:53

more overlap on high performance cams isnt only for the effect you mentioned. The exhaust valve opens much sooner in the cycle to "bleed down" cylinder pressure faster so that less power goes towards the pumping loss on the upward exhaust stroke.

also, gas flowing through a smaller tube achieves a higher velocity and a higher pressure loss i.e. backpressure (how i hate that word), not lower. there are other resonant effects which affect header design in addition to gas flow.

you seem to have low regard for OEM exhaust systems. What you said may have been true 10 years ago, but now almost every manufacturer who cares enough about high specific power output (for eg Honda) equips the engine with a header-type manifold. Most OEM bends are quite well-made and do not have kinks or significant cross-sectional variations to impede flow.

14th April 2007, 08:53	#140 (permalink)
ananthkamath BHPian Join Date: Jul 2005 Location: Detroit, Michigan Posts: 986	more overlap on high performance cams isnt only for the effect you mentioned. The exhaust valve opens much sooner in the cycle to "bleed down" cylinder pressure faster so that less power goes towards the pumping loss on the upward exhaust stroke. also, gas flowing through a smaller tube achieves a higher velocity and a higher pressure loss i.e. backpressure (how i hate that word), not lower. there are other resonant effects which affect header design in addition to gas flow. you seem to have low regard for OEM exhaust systems. What you said may have been true 10 years ago, but now almost every manufacturer who cares enough about high specific power output (for eg Honda) equips the engine with a header-type manifold. Most OEM bends are quite well-made and do not have kinks or significant cross-sectional variations to impede flow. __________________ Miata Turbo Is GO!! Last edited by ananthkamath : 14th April 2007 at 09:05.