The effects of exhaust energy on the performance of an internal combustion engine has been a hot rodders quest for decades.
Recently the many computer programs for sale and on the internet have shed some light on the subject in the form of the ANSWERS,, if the correct data is inserted.
In my opinion the key to understanding exhaust dynamics,, let's say the old fashion way,, is looking at Degrees Per Inch (DPI). That is to say the degrees the crankshaft rotates per inch the form of energy travels from the exhaust valve through the exhaust system and returns to the combustion chamber as a NEGATIVE sign helping draw in more fresh mixture.
This is where the old fashion part comes in,,,, simple math.
The 2 forms of energy we attempt to "tune" is the sound wave (Wave) and the physical exhaust pulse (Pulse).
They travel at vastly different velocitys. The Wave travels at approximatly 1700 FPS in the environment of an exhaust system and the Pulse most optimum speed is 300 FPS. Pulse speed can be controlled, some what,, by the ID of the primary pipes and the heat in the exhaust system. If the pipe length is correct for the Wave to return at overlap when both the exhaust and intake valves are open, and the Pulse speed is too fast or too slow, one or both of the valves will be closed.
Time is your common denominator. ie; revolutions per Minute,,,feet per Second.
Here's a little something to ponder: 6000 RPM is 36,000 degrees per SECOND of rotation.
Easy to see why some exhaust systems have a very narrow RPM sweet spot ?
Best, WP
