Thread: Ring gap for boost?

Hey im thinking about building my own motor for the sake of time, money and gaining experience. This is my first turbo build/car and i spent the money to have good quality parts and dont want to half-a$$ my investment.... I have a new set of 86mm 8.5:1 CP's, and i doubt everything is ready to go out the box. so i want to check with you guys to see what i need to do....



Edit: I found exactly what i was looking for! According to Cp's website on ring gap and also ring orientation. Here is the link in pdf format...
http://www.cppistons.com/LinkClick.aspx?fileticket=eBVGqvQcWj8%3d&tabid=61

Actually they are pretty close out of the box. Use the street specs if you want a tight motor with minimal blowby. I went with the street/strip specs for my JE pistons. .019" top ring and .021" for the bottom iirc. This resulted in more blowby than desired though, so if I could do it again I would shoot for .017" and .019".

Not sure, but the JE piston set I got wanted the bottom ring gap to be larger than the top. This is not conventional ring gapping tech. The bottom ring usually has a smaller gap in it than the top ring.

Well, I hope this helps. In all reality, the piston rings are prob at a perfectly safe street level boost ring gap. I've not heard of anyone having any ring-butting issues by just tossing the rings in there and not even checking the gap, but I wouldn't recommend it.


If I did it again, which I will soon, I would go on the tighter end of the spec. I don't believe that rings will start butting until ring gaps are below .012". But I would like to hear other's opinions and see what they think as well.

cp has specs for their rings and pistons. Use those specs.

I agree with Mike.

You can't go wrong with CP's ring specs. Technically, they're a LITTLE bit on the loose side for what they recommend, but even the boost spec gaps don't present much blowby on a street setup.

i cant remember but i think my motor is .017 top ring and .019 second ring

hmm well alrihty then i prob wont get to look at the specs of the rings for a couple days due to work but my next question is "How?" I would need feeler guage correct? and what if the gap is too big? too small? Thanks guys im pretty excited about doing this build, i picked up this motor and have been researching and buying parts since last summer.....I can almost taste that boost!

Exactly what I would recommend. Tight where it counts, no excessive blowby. And there is no way the rings will ever butt ends. They expand, just not that much.

For 2618 low silicon alloy... ~ 3.39" bore.

Piston to wall clearance- Tight end .003-.0035 Loose end .0045-.005

Lower clearance may cause issues when pistons expand. I run a .004" clearance to keep the pistons from slapping, but keep a save distance. The tighter clearances will NOT work for high hp turbo cars. Too much heat will cause the pistons to expand too much and contact the cylinder walls. Not good. For turbo run AT LEAST .004" to be safe. You won't see any piston slap until over .005" (not noticeable anyway.)

Ring gaps

Top ring gap: .017" moderate turbo/nitrous .015" NA. Race .019"
Second ring gap: .019" FI, .017" NA, .021" Race.

I think on the next motor I am building currently I am going to go for a tight ring gap. Even at .014" I don't think anyone would experience ring butting issues. I will either go with .017"-.019" or .016"-.018".

Tighter gaps have their benefits. You just don't wanna go too small on the gap or you could bind the rings together.

Keep in mind, stock cars run really small ring gaps. Though the stock cast pistons don't expand near as much, I don't think you would have any issues with the smaller gaps. Its prob more of a liability to run the tigher spec.

good luck.

I just run whats on the CP piston spec sheet for turbo applications.... The ones i just put in were right on the money right out of the box. And CP's rings from the several builds ive done are either dead on or very very close to dead on. Ive only had to file rings down on one build. Again it all depends on how good your machine work is too.

You need to run the spec they give you. Diff pistons wil be made from diff materials and will expand differently. USE THE MANUFACTURES SPECS