I've never read an engine test on a speed .15 (the full on race .15's) probably because I'd say it's near impossible to do on a bench. The nearest I've ever read was on the development of a .15 by Luis Parramon of Spain who set the current world speed record in a competition at 302.5Km/h (188mph). It took him 2 years working in an engineering laboratory at a university to sort the engine/pipe out and it gave 2.7HP at around the 40K mark (that's 1080 HP/litre!).

But that record was in a competition where you only have a limited number of attempts. The absolute speed record (where you can try all day if you want) is 335Km/h (208mph). If the first engine was doing its best at 2.7HP then this one would be producing around 3.3HP (the models are virtually identical so the drag is too).

BTW...this is all done on zero nitro fuel.