Please tell us WHY you THINK back pressure is needed on any engine size?
And what about the factory series racers with 1.5 or 1.6 engines running open pipes I guess their builders haven't read the same articles you have read.
yeah they are running open pipes. no cat, no mufflers.
this doesnt mean they dont need backpressure
lets say for example we have two engines, they are the exact same, they need to be, due to class regs.
one of them has a "normal" sized exhaust, whatever that may be, say 2" and one of them has an exhaust that is 6" the whole way.
what one do ytou think would be making the best power curve?
afaik back pressure is undesired on any motor setup
i believe the idea is that smaller motors can't maintain a high velocity of gasses through such large pipes i.e. b16 with 3" exhausts
the whole 'it needs back pressure' idea is a myth
it needs an appropriate sized exhaust to keep exhaust gas velocity high
too big exhaust, and the motor can't move the gas through the large diameter pipes efficiently
So U need to choose the right size pipe.Then are resonaors and cat's just restrictions then?
Read Vinny's post. He got it right. The idea is to maintain the exhaust gas velocity. For a fixed volume, the velocity decreases as you increase the diameter of the piping. Too small, and you create backpressure. Too big and you lose velocity. You want to go as big as possible without having the velocity drop too much. Of course, the volume of the exhaust gas is never constant. At low RPM, the volume is smaller. At high RPM, the volume is larger. So you choose your diameter based on the volume of exhaust gas at the RPM that you want optimum power/torque at. Hence street cars have a smaller diameter for low to mid RPM, while race cars have it larger since they stay at high RPM most of the time.
Cats, resonators and mufflers are all restrictions which slow down gas velocity. The are a must for environmental reasons in a street car. But for a race car, they are undesirable.
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Originally Posted by claymore
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