would the mahle (4032) piston beable to handle 11.5cr with nitrous on top?I agree with that. 4032 is great for street motors and just about any all motor build. The tighter clearances should pay off with better longevity of the piston itself and the rings (they're less exposed). The Mahle pistons are 4032, have coated skirts, and generally one of the best off the shelf 4032 piston makers out there. That's what I would use if I was going to start a new build today.
2618 can take more abuse b/c it has a higher tensile strength. That means when high HP starts pounding the piston, high revs start to stretch the piston, and high heat starts to soften the piston, 2618 has a greater ability to take the load without falling apart in a catastrophic manner. The downside is that the coefficient of thermal expansion is greater meaning you have less consistent skirt profile as temperature varies. This makes it a little bit more tricky to get daily drivable longevity out of a 2618 piston versus a 4032 piston.
and when you talk about the clearances are you guys referring to the piston rings?...
just tryin to get a better understanding