You are right in thinking there might be a problem with having slightly less HP. Actually, there is 25% less power, and a Raptor is not in the least overpowered with an OS 32. Most flyers put a tuned exhaust like the Weston Genisis on the .32 just to get adaquate power, and still wish they had more. Everyone who has tried putting OS .52 four strokes in 30 size helis has usually given up in frustration, they end up with a heli that just barely flies on a cold day and one that won't do even that on a hot day. A 40 four stroke will probably be even worse. The four strokes end up running wide open to barely get the job done, then they get hot and can't get the job done at all. The only helis that have worked with a four stroke engine have been the 60 size helis with a YS 90 ACH installed, and as Gordie pointed out, they had their problems. Good luck if you wish to continue the effort, but I would do a search on the forums first. After hearing of all the problems incountered, you might change your mind.