It depends greatly on the application wheather to use a 2 or 4 stroke. Ladyflyer, think you are stroking me, as the best engine recomended by those in the know for a Han 9 73" cap 232 is the Moki 1.80 2 stroke. The weight of the Moki ballences out the plane perfectly, & the power is grate for 3D. Balsa USA recomemds and built ther Phaeton 90 around a 120 size 4 stroke for power. I love the sound of a screaming 2 stroke on the pipe mounted to a sleek 40 size screamer. To me a war bird just does not sound right with out a 4 stroke out front. You can throw numbers, and terms, such as better transition, don't load up as much, around all day, but some ariframes beg for a certain stroke engine.