I'm a noob at actualy driving nitro cars in anger but I guess you could put a heavier oil in the center diff so if the front has less traction the front wheels will not spin that uncontrolled. I think the heavier the oil the more the RPM of the front and rear center drive shafts are the same and sort of dictated by the axle with the most grip. Maybe you are still a bit trigger happy on the throttle or the engine has too much torque.

I'm going for a 3,5CC engine.

@j_blaze

I guess I didn't read your post well, so please ignore my previous remark about how I didn't understand how it would work. I thought you were talking about the front diff.