Typically ( with exceptions ) if you are comparing engine sizes from the same manufacturer, as you are, then the engine with the higher displacement will be more powerful.

1/2oz does not make a lot of difference on a plane this size...

However USUALLY a .51 engine tends to be more powerful....

BUT, ABC cylinders often have tighter fit ( more compression ) so they may produce more power than a slightly larger engine...

That is why the given H.P. ratings are so similiar on the two engines.


And round and round it goes!


The difference in RPM's will hardly be noticible.
The difference between the two in power may not be noticible.

The question is which one will last longer.

Some ABC's fare much better than ringed engines... but the reverse can also be true based upon the ABC liner materials.

For me "there be dragons here", so someone more familiar with the metalurgy involved in ST engines may want to chime in.


But my ST .75's do leak like sieves... I'm not happy about this.

The engines run great. But I've gone as far as putting in completely new carbs to eliminate the leak.

I suspect that the carb is leaking along the rubber covered low needle valve area.

Everyone has a good laugh when I land my ST equipped planes and even though I have the carb fully closed AND I cover the intake with my thumb, the engine keeps running and running until I pinch off the fuel line completely... even then it takes a few seconds to turn off.