Barry Cazier,

In Cycles the 4 stroke would not have a chance with the similar 450cc 2 stroke.

I think to be fair in comparing the airplane motor you have to look at the weight of the motor not the displacement. Of course when you do that you need to include the muffler. This is where some of the new 4strokes really shine--saito 82,100,180, all YS's.

Fuji is making some larger gas 4 strokes- BF25 & 34. You can see them at Tower Hobbies.

I would not be too sure that in a matter of a few years you will see 4 stroke gas motors take over in the 50cc+ area. I not saying that it could not happen, I am saying that I doubt it.

Right now there is not a 4 stroke motor that I know of that I would put on a plane weighing 14+ pounds for 3D.

Another factor that has not been discussed yet is adding a properly tuned(power pipe for 3D) exhaust system on a 2 stroke. This can increase the response and power of a 2 stroke significantly.