What should my piston ring end gap be for a sealed power hypereutectic piston that is a 4.030 inch bore. It's a 383 stroker that will be driven mainly on the street, but might see some hard driving at times.

 

What Sealed Power states in their instructions. My Weisco forged pistons in my 383 worked out to 0.014" upper ring and 0.016" lower compression ring based off their clearance specs at a 0.030" over bore.

 

The instructions only stated how to put the rings on. There was no mention of ring end gap unfortunately.

 

Rule of thumb is .004" gap per inch of bore size, but you'd do well to contact the manufacturer and get the specific recommendation for your particular ring set.

 

Hypereutectic pistons shed heat far less than forged or even normal cast ones, therefore the rings get a good bit hotter, therefore their end gaps have to be a bit looser than others.

If you have a little too much gap, or even ALOT too much, the worst that happens is, a slight extra amount of blowby. (emphasis on SLIGHT) If you have ANY too little, even just .001", DISASTER strikes. The ends butt together when they get hot, which makes their OD greater than the ID of the bore; the least severe thing that will result is blowing the ring lands off of the piston, and can get ALOT worse from there. Up to and including, seizing to the bore, gouging it, and so on.

I know which side I'd rather err towards.

Rule of thumb for hypers is .0045" end gap per bore inch for a "normal" application, on the top ring; open up a half to a whole thou for a "hot street" or "street/strip" deal, and another thou if typical street amounts of nitrous or forced induction are involved. About an addl half thou to ¾ thou on the 2nd. I'd set up one like yours at about .020" on the top and about .023" on the 2nd, if it was mine.

 

What material and design are the Top Rings, and Second Rings?

We can provide a definitive recommendation with more information.
Sofakingdom gave you a great recommendation for not knowing more about what you have.
There are many factors to consider, and many variables (which you could minimize by posting the details).

 

A piston manufacturer has no idea what rings will be run on a particular piston. The combinations are endless.
That's why you need to ask the ring manufacturer what gap to use for your situation.
Usually, they are more than happy to help.