RE: Webra Speed 40 Q
Thats the Q500 version. I raced those for a few years.
Its a very good engine. Keep in mind the Q version dynamix carb has no idle mixture or true throttle provisions. It is simply intended as an engine shut-off.
Racing prop of choice was the APC 9x7.5, 8.75x8W or 8.75x7.75W. Your prop will depend on the aircraft it is installed in.
The stock Webra Q-500 muffler had in later years been supplied with an outlet restrictor. It is necessary to use this... the engine needs the backpressure. I also used a larger 8-32 pressure fitting for tank pressure.
Racing with SEMPRA down south, we were allowed to use aftermarket mufflers. Toward the end of their "reign", nearly everyone used the Jett or Nelson mufflers on the Webra .40.
I hope this is helpful.
Bob