MVVS GRRT- 40 F3D on Patriot?
I have the same engine but mine has the round exit on the exhaust. It does idle though pretty well to slow down for landings. But I know for my engine it took a 7.2 X 8.6 or 7.4 X 8 to get on the pipe. I also tried a 8 X 6 and that worked also but ai did have to shave the tips off some. This engine needs to rev to get the power to come on.
That was the only way I could get it on the pipe. Under the pipe it ran just like a regular sport engine and was not very impressive. But when the pipe kicks it you can tell what separates the sport engines from the racing engines. It is a total different ball game.
Also it is a huge gas guzzler. I can run a 6 oz. tank in 2 1/2 min max on pipe. Off the pipe it runs a bit longer.