Sorry to be so late in this thread, however I will say this. Back in the late '60s and very early '70s when I was very active in CL stunt, after leaving the USAF, I owned one of those Fox .40 Stunt engines. At the time I was using mostly Fox .35s and for competition, a GA rebuilt ST .40 which was a superior Stunt engine.

Using Fox Superfuel, 29% castor oil 5% nitro fuel I ran the engine for a couple tanks just to get a feel for it. I used a fat 11-5 cut to 10-5 for break-in. Then it went onto a Midwest 48" w-s profile stunt model -- ME 109 -- for over 3 hours of constant flying over a couple weeks. It then went into one of my original stunters and was flown in competition for several years until I became completelyinto RC after '73

The Fox 40 was equal to the Super Tiger in every respect. It started the first flip if I obtained the "bump" then flipped. It had plenty power and I still have one NIB if I should again take up CL.

Incidentally, I used OS and ENYA CL needle valve assemblies with the single hole facing STRAIGHT BACK. This technique takes care of many problems that CL Stunt pilots manufacture for themselves.