None, with .018 ring gap on the top ring. You ask in an earlier post about end gap and washing the cylinders down, could it score the cylinder walls, yes it could, i also think the 850 double pumper carb is too big for a 383" motor, no matter what cam you're running
With forged pistons, i would normally put .005/.0055 end gap per inche for gas, for nitrous i would put .006/.0065 for a 100/150 shot of nitrouus. I would have the piston to wall clearance set at .006 on forged pistons. Anything less you're asking for trouble. I don't care what Mahle recommends, they are in the business of selling pistons not building motors that have too live.
I'm as we speak building a 383" with hyperutectic pistons that will run on alcohol. It should make about 575 HP, and i will have .030 endgap on the top ring.
I should say that i'm not a fan of Mahle pistons, the top ring is too close to the top of the piston and draws a lot of heat.
I had friend put Mahle pistons in a 383 with an 871 street blower, he used their recommended end gap 5 lbs boost. The first time he got on it it pulled the top of all 8 pistons off, that was enough for me.
JMO
Zip.