Originally posted by PylonWorld
I was already thinking about being able to run a Q-500 timed engine with a Q-500 prop like an 8.75 x 9.25 ... but I don't think that would be legal ... I haven't seen the composite prop rule yet. But for Q-40 Sport with a TT Pro 40 and a 9 x 6, it should do well. 
Don,
The way I read the rules, using a Quickie motor spinning a bigger prop is perfectly legal for 422. You'd have to use a wooden prop though. Like you, I haven't seen the full text of the new CF prop rule so I don't know how that would apply but I'm pretty sure the rule states that it is just that one prop, in just that one size. It'd be too small for the 428 motor.
I've thought about this too and I wonder what kind of reaction I'd get if I went to a big contest like one of the Gold Cup races with a quickie motor hanging on the front of my Q40.
Turning a bigger prop would be a good way to limit the top end speed some.
As for the Thunder Tiger, as long as the muffler meets the dimensions specified in the rules (I'm pretty sure it does) and you use a wooden prop, this would be legal too. What kind of reaction would THAT get you?