I recently aquired an ACE ultimate bipe that reqires a 15-25 size engine however it has a .35 os engine on it, it has never been flown and was scetchy on flyin it without the right size motor, will it really mater? also I was going to try to get another plane to use that motor in and was wondering if i can use that 35 in place of a 40. it seems everything i like is a 40 size , will it fly right with a 35 instead of a 40? I aint really concerned with speed so much as making go fast enough. so can i use the 35 in place of a 15-20? what abot 40?