Bryan,
 The idea of an expansion chamber is thinking properly but off the mark. In a 2 cycle engine the expansion chamber works because the bottom end is a low
efficiency supercharger for the top end. Enough intake charge can be forced into the cylinder that it, (the intake charge), is running out the exhaust port.
The timing cone, the taper at the rear of the expansion chamber, forces this back into the cylinder. With a wankel the problem is reversed the rotor tries to
sweep the exhaust charge into the intake. The early rotary racers tried to solve this problem by running a constantly expanding megaphone from the exhaust
port all the way to the exit. This technique worked as it really moved the exhaust gas. It's problem is that it is UNBELIEVABLY loud. Not acceptable for our
use.
Bill Jepson

 
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