OS MAX-40F-SR STUNT

I'd be very curious to see that engine stunt. I know it came in different versions such as ringed and ABC. I would also like to add, they were extremely well made and no pennies pinched.

It's a nice looking engine, no doubt it would be a good runner.

These were the 'Chevy small block' of .40 R/C engines in the 80's-90's, well made, easy to needle and great power. The FSR series was copied by Thunder Tiger (Magnum) and sold by the thousands. But for a U/C engine not so much, they would be on the heavy side and unless you did some major re-porting you'd need to run it in a two-stoke mode with a big diameter, small pitch prop.
I'd guess and say it was a cost/production thing with the two piece case. Later O.S. engines went to a one piece and i remember claims of RPM gains by the one piece case being more rigid? I planted a .40 FSR one time and was able to replace the front end only (with a Magnum part) and save the engine.