Pardon me for throwing my two cents in, but I see a couple of differences between the way a pressure wave would travel in the 13B as opposed to the 20 B. Aren't the rotor TDC s different for the two engines? Isn't the tdc for the 13 180 degrees apart and 120 degrees for the 20 B? Also, with the 13b, you have the pressure wave ping ponging(that's a technical term) back and forth between the two rotors. In the 20B, you have the pressure wave from one rotor trying to get to the other two rotors, each of which open at different times. How you could do that, I do not know. With the 26B four rotor, you could have two separate mainifolds, like two 13 bs on one crank. Maybe people with larger brains than mine can conceive of how to tune a 20 intake, but I can't.

Brian Trubee

 
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