I would guess 1.62's with that pitch on a Simon. Eric says that they should be proped from 5600 to 6100. I can turn a 27 to 6100 with 1.75's on a stock 250xb. Kind of curious what speeds you are seeing also. I'm building a similar motor! Chris1978 has the same setup as you 21xdc simon 250.


Modified by Todd D at 11:33 AM 12/11/2008