Piston ring gap

[Monty]

Anyone have any guidelines for setting top and second piston ring gaps. I know that on NA engines, .004" per inch or bore is the general guideline, what about turbo setups? This is for a twin turbo SBC 427, 4.125" bore, forged JE pistons.

 

[Intercooler]

This is for Total-Seals as I have the sheet in front of me and for blown gas (turbo, supercharger) they suggest .007"/per.in on top and .006"/per.in on the second with oil ring at a minimum of .015". From what I recall with Sealed Power rings it was the same. I have my 3.8 set at .021" and .023". I would use .006"/per.in at a minimum.

 

[Monty]

Thank you for your reply, that makes sense. I don't think I'll be able to run more than 15 psi of boost on pump gas, if that, even though it's intercooled and I lowered the CR to 8.5. Plus the top ring is .310" down, that's why I thought Fast Time's recommendation to be a little wide. I can understand it on their turbocharged NMCA/NSCA or NMRA racing engine's where they're running almost 40 psi of boost...

I want to be safe since this is a street car, but I don't want to get excessive with the end gaps to the point where blow-by or oil control become problems.

Any thoughts on running the second ring wider than the top? I read on the SpeedPro site where this arrangement produced better results by preventing the buildup of pressure between the two rings, lifting the top ring and creating excessive blow-by.

 

[Turbo 6 Justin]

I would also stay just a tad above the .006 per inch, On the 3.8 bore I aim for .22 top .24 second. as for a larger second I have done a lot of reading here and other places and have talked to a lot of people (hey I like to do way more research than I need to do) and I definitly buy into the larger second gap convention.

on your motor I would probably run .025 top 26-27 second, that should treat you real well on 15psi and be plenty safe for a 'bit' more boost on race gas

 

[Intercooler]

FWIW I just spoke with Total-Seal for about an hour concerning my rings. They gave me a sheet that said to use the mfg's specs when using Hypers so I did or at least I thought. After talking with them they said if I have Total-Seal top rings (which I do) all the heat will be right there so I should open up to .007" or .027" on the top. Back to opening up the rings! Now I will have .027" top and .023" second which according to them is perfect!