Mike, I've filed all of the top rings for my pump gas 355 sbc. The top rings are now .020" for the majority with maybe 2 cylinders at .021". Pistons are Speed Pro H345NP. Rings are Speed Pro R9343 +.035. This WILL get sprayed on occasion with a 125 nitrous kit. Ring data calls for Top ring .020-.022" for"Nitrous Oxide-Street" & 2nd ring .024-.026" for"Nitrous Oxide-Street." What do I need to do ? Should I go back and open up the top rings to the max of .022"? Do I need to set the 2nd rings to the max of .026 " ? What happens if a couple of the top rings end up over the max (023-.024")? What happens if a couple of the 2nd rings end up over the Max (.027-.028") ? I know it's instant death if any of the rings butt together while I'm spraying. It has taken forever to get this far & I don't want to kill it once I get this thing going. Thanks. Dave H

I would put the rings at the max spec myself for two reasons... one: the pistons are hypers and will swell more then a forged piston... secondly: a 125 hp shot many times turns into more.

Even though it was not asked... I personally would be very careful spraying a Hyper piston motor. I would keep the shot 150 or less and make sure she is running fat and you should be ok.

Dave,
First let me say I do not do hardly any Nitrous stuff but,,,,,,

While I am not advocating the use of Nitrous with Hypereutectic's,,,,,, :D
A LOT of people have had no problems running 125-150 on stock engines for years.

You will be fine at .020 top with 125 of spray as long as you keep the tune-up from going lean.

Hyper pistons do not swell more than any other piston.
The only piston that needs more gap is the KB & it has to do with the placement of the rings along with being Hypers.

Fed Mog pistons run basically standard gaps as the rings are lower.
With only 125 I would not be afraid to run .018 top again keeping things on the rich side & without a ton of timing.

The second ring will be fine at .024 & I would run it the same as the top at .020-.021 without worry.

My standard gaps are .004/ inch top & .0045/ inch second or .016/.018 for a 4" bore (non nitrous)
I have tried closing them up & gained nothing & opening them up & lost nothing that I can measure including HP or blowby.

I have found that in a 4.125 bore in a pretty serious 332cu in. 18 degree deal that the top rings show signs of butting at .014 but this thing makes about 670HP at 9300 ;)