RE: looking to slow my trainner down without a new engine?
i agree with the last statement. a 46 flying an 11 x 6 on a trainer is slow enough. there is no need to fly any slower than that. i flew that combo on my first flight and it was easy breezy. moving to a 12 x 4 may slow it down but really there is no need. i can't imagine a situation where that kind of prop would be needed for training. as hossfly said, throttle control will be the way to go IMHO.