I'm gonna bite on this bait.
No one seems to be able to give you the answer you are looking for, and I don't expect to either.
However, I will take a stab and write what I think are the two important characteristics. I won't even use terms like backpressure. Backpressure is a consequence of the pipe diameter and the pressure drop that occurs between the cylinder and the atmosphere at the end of the pipe.
I would have to say that you would want exhaust components that will tend to keep the exhaust velocity high and still flow the required volume of exhaust at the appropriate rpm. Lets not forget that as rpm changes from low to high, there is an increase in the volume of exhaust per unit time. This means that you have to optimize pipe diameter based upon two variables, Volume and velocity.
I would attempt to do this by picking the rpm where I wanted to optimize those variables in the middle of the rpm range dictated by the shift points. In my car, I would pick around 5,500 rpm.
That volume of air going into the engine at this rpm would be on the order of 300 cfm. This isn't necessarily the same volume coming out, but I don't have any data on that.
I dug up some data from fluid dynamics.
The average viscosity (n) for gasses that make up combustion exhaust is roughly:
n=3.5*10^-5 N-s/m^2 or n = 0.035 centipoise
I have equations that are derived from the Navier-Stokes equations that will give max velocity for fluid in a tube, volume flow rate, and the velocity profile. Whats the point anyway....
I am not going to finish this analysis because I haven't found in the past that many people even care to go this in-depth. They usually want the answers handed to them, I know I sometimes do.
So at this point I have to say that the question is too complicated for me to answer accurately.
I do not have the experience to properly size an exhaust system from an engineering perspective.
However, I know that automotive engineers must have plugged and chugged through all of the fluid dynamics and come up with the 'solved' equations
that are now shortcuts for the rest of us.
So Terry, you must have access to them....What are they?
Tom
