Originally Posted by #Rotor (Post 1309968)

Harmonic tuning...

It basically works like this... if a positive pressure pulse is sent down a tube, the moment it reaches the end of the tube, a negative pulse of almost equal amplitude, get's sent back up the tube...at more or less the speed of sound. Heat, gas pressure, velocity, etc etc etc, plays a role in this speed, complicated, not going to go there... :)

now calculate how far the pulse will travel at more or less the speed of sound, in the time it will take the exhaust valve to close again. Devide the distance in 2 and you have the length of each exhaust runner for the engine to be tuned at that RPM.

don't worry about the positive pulses, they still carry on after going through the collector.


exactly the same for the inlet side, there it's just a negative suction pulse getting sent out from the valves, through the inlet runners, ITB's and when it gets to the mouth of the ram-tubes, a positive pulse goes back in, getting to the valves just as they are about to close... ramming that extra little bit of fuel-charge in past the valves before they seal shut....

then you can start to play with cones, like in the exhaust of a 2-stroke engine... Now you can stretch that rpm range out, giving you a much more manageable power-band, so to speak.

it is this harmonic tuning, that requires a NA exhaust manifold to be equal length, so that the pulses are evenly spaced at their tuned RPM range.