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-   -   Ring gap & head stud confirmation for 2.7 (http://forums.pelicanparts.com/911-engine-rebuilding-forum/1159146-ring-gap-head-stud-confirmation-2-7-a.html)

Dpmulvan 03-23-2024 07:16 AM

Quote:

Originally Posted by stownsen914 (Post 12218488)
I assume it's due to aircooled running hotter than the more typical water cooled applications covered in CP's published specs. I confirmed with a Porsche engine builder. This was an area I had no expertise, so I deferred to theirs.

The hotter an air cooled motor gets the more the aluminum cylinders expand. I guess it boils down to expansion rates between piston, rings and cylinders. I’m not arguing with you, I’ve got a set of these holding up a recent build and it’s sort of ridiculous that we can’t nail down numbers to go by. I guess maybe it’s worth the extra money to just stick with Mahle next time.

stownsen914 03-23-2024 10:06 AM

I also found it surprising that there wasn't more consensus on this.

As for heat, expansion, etc., the aftermarket piston manufacturers like JE and CP give different ring gap numbers for street/strip, circle track, boosted race use, etc. My application is race, so wound up using numbers closer to the "circle track" recommendations.

I also kept in mind a saying that a knowledgeable fellow shared here on the forum once:
Big ring gap = big catch can
Small ring gap = big trash can

I erred a little on the large side probably.

PeteKz 03-23-2024 03:10 PM

It will run just fine. What little difference it makes, you won't be able to feel.

Dpmulvan 03-29-2024 06:53 AM

Quote:

Originally Posted by stownsen914 (Post 12218628)
I also found it surprising that there wasn't more consensus on this.

As for heat, expansion, etc., the aftermarket piston manufacturers like JE and CP give different ring gap numbers for street/strip, circle track, boosted race use, etc. My application is race, so wound up using numbers closer to the "circle track" recommendations.

I also kept in mind a saying that a knowledgeable fellow shared here on the forum once:
Big ring gap = big catch can
Small ring gap = big trash can

I erred a little on the large side probably.

Any problems with rings seating or oil consumption?

stownsen914 03-29-2024 09:05 AM

Assembly is about the start. I'm hoping to be able to be able to answer that question in the coming months.

Dpmulvan 03-30-2024 04:01 AM

Quote:

Originally Posted by stownsen914 (Post 12222592)
Assembly is about the start. I'm hoping to be able to be able to answer that question in the coming months.

I ended up going with .018 top and .020 2nd your cp’s might be different, rather have a little blow by than seize it up.


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