Difference between 1974 Yamaha GP 292 and SM

[deepstroker]

I know the GP is a Reed motor and SM piston port what is the HP can you make a SM run as good as a GP and is the chassi diff. someone said SM wider ?

 

[montynormand]

I think the 74 sm and gp chassis is the same. Port timming is really different between the reed and piston ports. Stock to Stock the Piston Port will not produce as much HP as the reed. I have a GP292 piston port producing over 50 hp. Rummor has it that there are guys out there with over 60hp with the reed motors