Ring end-gap.
 

Anyone got the ring end-gap specs for the top and second compression rings for a 4.280 bore?

What is the piston, cast,forged or hyputectic sp? Ironman

It appears there is a major difference if forged vs. cast pistons. Merc says the following: Cast pistons (std bore,4.250) top ring=.010-.018, second ring=.016-.024. Forged pistons (std bore, JE/GM, 4.250)top ring=.015-.025, second ring=.015-.025. With a .030 overbore, I would add .001 (max)to the min/max numbers. Also--these #'s are for normally aspirated engines. S/C specs are different.

I'd suggest .0045 per inch of cylinder bore in a naturally aspirated application. In your case that's .019 ring end gap. My personal preference is to match the top and second ring gap, but there are all sorts of opinions on that. If in doubt, go bigger!! To much gap is much better than contact.