Originally Posted by xfirer1guy
Dont you always tune for the first mode wave? The energy in subsequent waves is legligible compared to the resonant frequency.
Due to the high redline and amount of camshaft adjustment of the S65, it is possible to tune for the second, third wave, or fourth wave.
I am not sure if they are actually using the third or fourth wave, but the torque curve of the engine is so flat that they are not using only the first wave, it would be impossible to do so over the 6000RPM that the torque curve stays nearly flat!
To answer your question, the energy in the subsequent waves are reduced, but they are still very usable. One thing that is of note, is that as the RPM's climb, the exhaust scavenging effect increases enough to offset the reduction in intensity of the pressure wave in the intake. This scavenging effect is also helping to pull new mixture into the cylinder under valve overlap........ I am sure this is one of the main reasons for the nice equal length primaries and nicely designed merge collectors on the factory headers. Loss in this scavenging effect may be the reason why some x-pipe setups seem to put a hole in the bottom of the torque curve on the S65.