Okay, I am not going to pay Merc prices on these things Can anyone give me a line on stock rings for an HP500 EFI? Looks like what are in the pistons are standard 1/16 4.505 rings and they are TOO tight. So I guess these are metric right? Where do I git em?

They are metric but available. Check with a machine shop for a source. Hastings and Speed-Pro are a few manufacturers, or go to JE Pistons. Good Luck.

I have bought them in hastings before,as far as standard rings go they were exspensive to the tune of 175$ or so but they are out there, Smitty

I used part # 12524293 from GM perf. parts on mine.

Jegs and Summit list them too.

As Artic says hasting does them too.

Either way, it beats the $83.61 list merc wants for 1 hole

I typically use Speed Pro on the stockers. I can get them for you. Give me a shout if I can help.
Eddie