Gentleman,

as we all know the key for serious speed is founded in the airframe/airfoil. That’s the key challenge, nothing else!

A highly competitive engine/pipe/prop combo to be perfectly matched to that specific airframe is obligatory.
Preferably a highly modified engine, but as said before that’s not the real challenge...

BOTTOM LINE: The contest MUST be defined by motor size classes in order to let the special revver brother win who realized the absolutely best aerodynamics.

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BTW: Chuck is right. Please don’t use radar guns. The airframes with the highest speed potential will definitely be too narrow to be measured accurately during competition. Use DOPPLER instead which is very cheap and precise. But don’t forget the barbecue grill