CP pistons - which rings to use?

stownsen914 · 02-12-2022, 06:51 PM

For CP pistons, do folks use the rings that come with them? I heard one recommendation to use Total Seal rings (their conventional style ones). What are others doing?

Jeff Alton · 02-15-2022, 08:25 AM

We use the rings they send. Very good. We have also used Total Seal with a gapless second and been very pleased.

175K911 · 02-17-2022, 11:42 AM

I used the rings that came with my 3.6 CP pistons. Nice fit in the ring lands and I only had to file 3 rings very slightly to get the right end gap. Definitely jewelry.

MST0118 · MST0118's Garage

Can you use Goetze rings with cp pistons? Might be a good fit if using cp pistons with Mahle cylinders.

Jeff Alton · 03-15-2022, 02:46 PM

Ask CP to see if the sizes are correct. But why? The rings they send are very very good.

Cheers

MST0118 · MST0118's Garage

My thought is that the Goetze rings might work slightly better with the Mahle cylinders since they typically come with Mahle pistons/cylinders.

Jeff Alton · 03-15-2022, 07:33 PM

Ok, ask CP. They spec the ring pack based on cylinder wall. The ring pack for an Iron cylinder is not the ring pack they spec for a Nickasil wall. They know what they are doing. They supply pistons to Porsche for some of GT series cars....

But, by all means, ask them. Jerry is the Porsche Guy to talk to at CP. He does all of our logistics for our custom CP piston orders.

Cheers

winders · 03-15-2022, 09:21 PM

Quote:

Originally Posted by MST0118

My thought is that the Goetze rings might work slightly better with the Mahle cylinders since they typically come with Mahle pistons/cylinders.

Why would you think this? Just because CV joints come with a particular grease in the box doesn't mean that is the best grease to use.

It's not like Mahle use a unique material to coat the cylinders. If anything, I would expect the rings package CP uses to be better than what Mahle provides.

KTL · 03-16-2022, 07:48 AM

Also keep in mind that the CP pistons use a different size/thickness of rings. In other words, don't go thinking that you can buy a set of 95mm Goetze rings (that are for the stock Mahle pistons) and they will fit the 95mm CPs

CPs use 1.0 top, 1.2 second, 2.8 lower oil control rings

Goetze or Mahle are 1.5, 1.75 and 4mm respectively

MST0118 · MST0118's Garage

KTL the difference in size may be the answer why you might have to use CO rings with pistons.

Scott, based on other threads here, there have been discussions that Goetze rings have options that are a softer and work well with Mahle 4032 alloy cylinders that generally have a lower RA of roughness of 3 - 5, so they may have less friction than other rings.

Some of the CP nitrided rings appear to match a higher RA cylinder surface like 15. I am sure CP has a variety of rings but why go with something else if you know that the hardness of the Goetze rings match well with Mahle cylinders with all other variables being equal? KTL raised a valid point about size of rings so that is probably why it’s not a good idea.

winders · 03-16-2022, 07:10 PM

The fact that CP makes pistons specifically for Porsche applications means CP is well aware of the material of which OEM Mahle cylinders are made. It also means they know what ring material and hardness is appropriate.

MST0118 · MST0118's Garage

Sure CP knows Porsche and they work. JE and total seal also make rings that work. But I would also say that not all “working” rings are created equal and some may seal better and have less frictional losses which may free up some ponies or be less harsh on the cylinders.

winders · 03-17-2022, 09:41 AM

If you think you are smarter than CP, go ahead and source your own ring package for CP pistons....

KTL · 03-17-2022, 10:28 AM

I would do what Jeff suggested and contact CP directly. We already know that their spec sheet, while detailed and informative, isn't giving us the best information for the desired roughness.

cylinder finish issues

Me saying that doesn't imply that their rings aren't properly spec'd for the cylinders. All i'm saying is we should get the roughness/honing spec from CP. This isn't as big of a concern with new cylinders, which should possess a honing/roughness value that's acceptable. At least that's how I feel in my mind, but maybe i'm wrong.

I'm more concerned about folks who get re-plated cylinders, be they same bore size or bored out bigger, because the platers like US Chrome or Millennium don't know your application. But they should certainly ask because they need to put a roughness value on their honing and can't just assume some generally accepted value?

Dpmulvan · 03-18-2022, 04:00 AM

Quote:

Originally Posted by KTL

I would do what Jeff suggested and contact CP directly. We already know that their spec sheet, while detailed and informative, isn't giving us the best information for the desired roughness.

cylinder finish issues

Me saying that doesn't imply that their rings aren't properly spec'd for the cylinders. All i'm saying is we should get the roughness/honing spec from CP. This isn't as big of a concern with new cylinders, which should possess a honing/roughness value that's acceptable. At least that's how I feel in my mind, but maybe i'm wrong.

I'm more concerned about folks who get re-plated cylinders, be they same bore size or bored out bigger, because the platers like US Chrome or Millennium don't know your application. But they should certainly ask because they need to put a roughness value on their honing and can't just assume some generally accepted value?

Cp rings are good for an RA of 15 to 20.

KTL · 03-18-2022, 04:39 AM

Quote:

Originally Posted by Dpmulvan

Cp rings are good for an RA of 15 to 20.

The contribution/feedback is appreciated. Could you elaborate on that a bit further than simply stating what we know the CP document says?

stownsen914 · 03-18-2022, 04:40 AM

Lots of opinions, thanks guys. To be clear, I do have the CP rings that came recommended for my application. I'd had a recommendation from a builder to use another brand, so wanted to get some opinions about the suitability of the CP ones. I think I'll use theirs.

stownsen914 · 04-21-2022, 07:47 AM

Follow-on question about ring gaps as I'm getting ready to assemble. 100 mm Mahle Motorsports nikasil barrels, CP 12.5:1 pistons, race application.

For performance normally aspirated engines, CP's web site suggests .0045 - .0050" per inch of bore for the top ring, and .0050 - .0055" per inch of bore for the second ring. For my 100 mm pistons, this would be ~ .0018 - .0020" total gap for top ring, .0020 - .0022" for the second ring.

I got a different answer when talking to one of the CP tech reps, who said for normally aspirated, air cooled race application he recommends .0022 - .0024" total gap for the top ring and .0026 - .0028" for the second ring.

Enough of a discrepancy that I'd like to hear what others are doing.

Jeff Alton · 04-21-2022, 07:25 PM

Email Jerry at CP and ask him, if that is not who you talked to.

Cheers

G450X · G450X's Garage

Similar question on rings…

I have been looking for virtually nonexistent new Goetze rings for my SC short stroke (3.0 to 3.2) Max Moritz P&C set, odd size 1.2/1.2/3.0.

Has anyone used CP or Total Seal custom rings successfully on these?

I have also seen a recommendation for recutting the pistons for a more common size?

Thanks