Bo,

I have discussed the whole setup on the thread sticky in the regular pattern forum. I am using the ESComposites 40G pipe and Hatori 2501 header plus a 4" extension to the header. There's a lot of info in that thread and frankly I forget some details and I have to look up myself from time to time.

Interesting question regarding damaged equipment from vibration of the gas engine. I have not yet had any damaged equipment. 10 years ago when I was flying Webra glow, I had a servo fail on aileron. Come to think of it, it's the only failure of that kind I recall in about 7000 flights over the past 30 years or so. Even when I flew non-iso mounted 60s in the 70s/80s, don't recall failures caused by vibes. On second thought, I remember control clevises wallowing out servo arm and control arm holes in the days before ball bearing and ball links. Every year or two, these were replaced.

I have the GF40 four stroke. I got mine at around 650$ if I recall. I have not run it but have heard it and it sounds great. It should work fine with the ESC canister Ed Skorepa sent me. The weight delta is a concern and its performance is probably not as good as the 33. Suitable for F3A? Possibly....it will turn 20x8 props according to the instructions. In practice, if it turns the 20x10 at 7k, any F3A model could be flown well except maybe a two meter bipe. The 33 will spool up to7800 and rip the 20x10 on premium gasoline. It's way more than needed.

a better option for the really beefy 2 meter Bipes is a 40cc twin on twin pipes. I have the engine and pipes but unless I designed it myself, no bipe ARF. This engine should turn 22x8 pretty well and will be plenty for a 12# bipe. It's only 25 grams heavier than the 33.