25-10-12, 06:49 AM
(24-10-12, 09:28 PM)tomlinscote link Wrote: Can I ask a qn? How does exhaust pipe length make a difference to power or torque I have heard about back pressure but never quite got the hang of it, if you didn't even have an exhaust manifold just let the gas out from the cylinder head surely that would be easier for the engine, and yep I get that you need to control where the gas goes and sounds like but ideally........??
P
Exhaust design is part engineering, part physics and part black magic. I am not an expert and it would be far to complicated for me to try and explain how it works, but there are lots of books on the subject, Motorcycle Tuning (Four Stroke) by the late great John Robinson explains a lot of it.
Every exhaust needs tailoring to the intended use of the vehicle and is therefore a compromise for road vehicles as the manufacturer has to cover many operating conditions. A Drag racing car with a Supercharger might use manifolds as short as possible to just clear the car, as things like scavenging, noise etc are of no concern
Cam timing, firing order, rev range, length of the primaries, length of the mid pipe, configuration of the exhaust ( 4 - 1, 4 - 2 - 1, 4 - 2 - 2, 4 - 1 - 2 etc) all have an effect on how the exhaust works.