ORIGINAL: fireman7875
Mine is the S1-A. I will probably try a .25 That's about the only displacement that I don't have right now so I suppose that's as good an excuse as any to buy a new engine, right? As I remember, my .35FP had waaaay more power than I needed but it flew great!
Brian
My best flying Ringmaster was also an S-1A with a Fox 35 spinning a Master Airscrew 9.5-6. With the Fox, just make sure you use a high oil content fuel - 28 to 29% is about right.
A modern 35 or 40 is just way too much for the 'ring. An LA 25 or the new Brodak 25 would be an ideal match and you can use more traditional fuels with 20-22% oil.
I once flew a Flite Streak with an FP 35 and it was way overpowered.