Dave. No easy answer to this one. The prop has to be matched to the motor characteristics. A 35mm prop is about the right size for yours, and possible an "S" pitch 35mm two blade plastic prop will add a bit more speed to your boat. Dont be tempted to fit anything larger! it will overload the motor.

Unfortunately there are loads of different 540`s out there, MFA do a "cooking" , relativly low powered one, or there are more than a few hot motors about.

I know this is not a lot of help but the motor may well NOT be marked up with its type so identifying it will be a bit tricky. Buying a new one would guarantee the type…a Graupner speed 500 for instance…however anything much more powerfull will begin to strain and overheat your ESC. The next up Graupner 500 draws a nominal 17A according to the blurb, for instance, compared to 9A for the speed 500. This will give much reduced run times to boot.

Ashley