I asked the question here a month or so ago about props on a RT188. I had a Lazer II 21p. After hearing the comments I put a Lazer II 20p on and that to me is the right one (it came with solid plugs). I went from 43 to 46 mph at 5600 rpms, The hole shot was already good but now it's great and it handles much better. Thanks for all the advice.