I know .004" per inch or bore is generally used for NA engine's, but what about turbo applications? This is a TT SBC 427, 4.125" bore, forged JE pistons, street engine, pump gas.

 

Since Turbo's tend to run a little hotter you should open the gap up a couple thou. I'll check around today and see what we run.

.016" Compression ring gap. That's going to be the biggest gap because it's the hottest ring. Hope that helps

 

Thanks for the reply. .016" seems pretty tight for a forced induction application. I ran .016-.018" on my 650hp NA SBC 427. My machinist recommended as much as .030"-.032", but he normally deals with turbo/super charged NMCA/NSCA and NMRA racing engine. So I thought that seemed a little wide for a low boost (15psi or so) street engine. I was thinking something like .026"-.028" for the top, and .024" - .026" for the second ring. I was just wondering what the other forced induction guys set there's at. I'm starting the final assembly tomorrow evening, and we're dynoing next weekend.

 

.016-.020" is what we set the new 6.0L Powerstroke to. Going wider never hurts endurance, but can effect performance. Whatever you deceide, good luck on your build.

 

ATO, thanks again!

 

check out your post over at the NMCA board, the guy that responded seem to know his stuff.

 

Thanks, I forgot I also posted over there...

 

Monty, we used .028 on my top ring and .024-.025 on the bottom ring.

We went by the instructions that came with my pistons and were liberal with the top rings. If they filed a hair over were not too worried about it due to running higher boost levels.

Good luck.

 

Sealed Power recommends .006" of gap per inch of bore diameter on a supercharged application. I imagine turbo would be the same.

 

.026 top/ .024 bottom here!

 

Thanks for all the feedback. I ended up going with .026" on the 1/16" stainless steel top rings, and .022" on the 1/16" cast iron 2nd rings. I dyno next weekend, so I'll find out then if it's okay.

 

I'm .020 on both.

 

.026 on both for me, 8 Lbs. of boost, 355 CID engine, 144 Roots Blower 220% overdrive. Solid bottom end. 28* timing. 550 horsepower @ 6500 Rpms... then boost falls off bad, so i shift @ 6200 Just in case.