I'm presently flying the MVVS 77 with short pipe on a sport ARF, still in its first gallon, getting 11,100 on APC 14x6, still nowhere near leaned out. Runs strong & steady, impresses everyone who has seen it fly. I've yet to find anyone who has put the MVVS 91 on a pattern plane, but I'm eager to try it--inverted mount, rear exhaust & short pipe, all I need is a plane that the engine/header/short pipe will fit readily.