Mopar R1 block

What’s thick?
A bit depends on what you start with and what your OK with in how thin it gets but the least amount of overbore is where it is at for cylinder strength for a non flexing cylinder leading to better ring seal, ring life, piston life, cylinder life. More power is made and retained.

You gain little in terms of power and engine size with an over bore. If your racing the engine/car in heads up and that’s basically an unlimited type of class, build what ever, the only thing important is the win, then some excellent gains can be found with a larger bore.

A larger bore gets more air and fuel in the cylinder, unshrouds the valves more for better filling and exhaust.
The cylinder wall should be good enough to support the power intended. In this area, thicker is better all the way. If you can have a 4.180 bore and still have a nice thick cylinder wall of let’s just say, .300, your in good shape or sure.

What is thin? .030 Race at your own risk.
Is that a Addition to the line? Absolutely not!
I knew a fella running low 12’s in a heavy-ish Duster with a .030 thin spot cylinder.
Do I think it was a good idea? Nope!
But if you don’t care, have at it. When it blows up, laugh it off and carry on.