Contour Enthusiasts Group Archives Forums Modifications Duratec Performance ? about back pressure how little is to little?

I think back pressure is a myth. I think when you open the exhaust, you change the RPM point of maximum scavaging. That is, where exhaust gas leaving the pipe effectively creates a vacuum in the cylinder, helping pull in more air fuel mixture.

Larger diameter pipes mean lower exhaust gas velocity. This means less scavaging.

Of course, at higher RPM's there is more exhaust gas trying to get out, so it must go faster to get out.

So larger pipes can improve peak HP, but usually at the price of a bit lower low end torque.

So if you've opened up the exhaust, you probably have a bit more on the top end.

The question is, where do you spend most of your time? Top end, middle, or bottom end.

I reserve the right to be wrong, I'm an EE by training, not an ME.

Cheers,

TB