That's not a cut and dry answer. It all depends on compression, fuel type, intercooled/non intercooled, afr ect.
Just thought about it, are you sure you're melting Pistons? If afr is right, and you're intercooled I'm willing to bet ring gap is to blame.
If gaps are factory, during a 1.5 mile run they'll expand enough that the edges butt together and break the top of the piston off. That's why on this bike when we did the spacer we also opened up that ring gaps.
