hi guys my friends xxx nt turns to the left and sometimes to the right when the gas is applied. It doesn't do it in the grass
only on the race track which is hard clay. could this be the ball diff?

probably. If your not spining out from heavy acceleration then it's becuase one wheel is spinning faster than the other or the other is not spinning at all and the cars being steered from the rear.
try tightening the diff.

thanx I'll give it a try

In many cases, its called torque steer.