Quote:
Originally posted by VieT916
The thing with exhausts is to eliminate backpressure while increasing the velocity of exiting exhaust gases. Think of a hose with an adjustable nozzle on the end that can make the opening small or big. Secondly, assume the water pressure is constant. If the nozzle's too small, not enough water comes out, but it exits at a high speed. Too big and a lot of water comes out very slowly ... too slow, in fact.
That's the way an exhaust (the "hose") works except the exhaust gases (the "water") exit in pulses -- four pulses for four cylinders, eight for eight cylinders, and so on. The idea with an exhaust is to match the piping size to make these pulses leave the muffler as quickly as possible but without restriction.
In essence, you don't want backpressure; you want extremely high exiting velocity for exhaust gases.
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This is good and dandy, except, that unlike the water hose, the gases do not always have constant pressure, higher RPMS give the gasses higher pressure, So in Essense, at low RPM's back pressure is needed to move the gases out quickly, and at High RPM's .. Back pressure is bad...
and who races in low RPM's ?!?!? hence my orginal saying that backpressure is bad..