my malossi gr2 50cc is faster then my malossi 70cc... Faster off the line and around the same the in the mid then pulls to much higher rpms for faster speeds without any porting work done to either cylinder, just case match to the polini race case. But the clutch pulley was the magic sauce for the 50cc. The 70cc has enough torque to pull the bike into the powerband the 50cc needs the HP generated with the pipe to pull you along.
-naz