Put a Ring On It - Piston Ring Discussion

It’s been many years since I recall much discussion about piston rings for the M96/97 motor. Quite a time ago, Ahsai got quite in depth with his reasoning, selections and installation during a rebuild. With so many different paths being taken for rebuilds or refreshes, I wonder what the schools of thought for piston ring selection, gaps, etc are today. For instance, when my engine was rebuilt over 5 years ago, the shop (a race-oriented facility) planned a slightly larger gap for the oil control ring specifically to allow for a small amount of extra lubrication in the higher performance engine. Seems to me there are more options due to improved research and product development/availability as the M96 and M97 non-turbos mature. As more engines are reborn, I see displacement increases more the norm. I’m sure there are some significant differences in what’s required for a stock rebuild vice a performance or DE build. Are there certain ring sets best matched with particular pistons or bore materials? Have there been any metallurgy improvements? Are certain rings proven to be better than others? I’d like to get some current input for some methodologies behind ring selection for our engines. Historical perspectives also very welcome.

Out of my technical depth, but interested in learning. I would expect most of this type of info would be held as trade secrets by the folks that do the work to understand designs/issues.

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True, to the extent that a particular gap or tension may be closely held, but the discussion behind the selection or installation is what I�m after. More possible topics to touch on: Do particular combos of ring and piston sets play together better than others? Is there a proven benefit to running a slack oil control ring because a block doesn�t have squirters in �x� or �y�? Do you make a different selection for a race build vs a daily-driver stock build? Rhyme or reason for how the name brands combine pistons and rings? Is there a particular trick or procedure that can be shared? �Been there, done that.� nuggets? Total Seal, Mahle, Goetze, OE (whoever that is), etc�several choices. Ring sets are one of the cheapest components of a build, but a poor choice can affect the performance and durability of a very expensive motor. Plenty of folks on this forum have rebuilt gobs of motors and they all have cautionary tales to tell. We�d have a little better knowledge and data base: FYI for the DIY and for the customer trying to make informed choices when talking to an engine builder.

These may be of interest. You Tube You Tube

^^^^ That’s exactly the kind of stuff I’m talking about.

Happy my trolling style agrees with you ! You Tube You Tube

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Ha! Too soon?

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If I'm gonna be something - I just want to be the best ! Enjoy the vids on what is hopefully a peaceful Sunday. May I suggest some (many) Bud lites to accompany you during your theatre time, what a combo

Before considering the rings, you must determine what cylinder material and coating/ plating that you'll be using. At the end of the day most of the things that impact the piston ring decision are tangled into the bore they'll be sealing against. Once cylinders are selected, then yo can discuss ring tension, ring coatings, and styles of rings. You then have to ensure that the cylinder surface finish matches the ring characteristics.

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FSI offered CP pistons with the no gap ring for my elective Stage 1 build. I jumped at the chance and added race level balancing and the high output ignition coils. I can�t imagine FSI did not weigh all of these considerations for use with nikkies. My experience to date confirms Lake�s findings regarding oil pressure and coolant temperature. Oil pressure at idle is ~3 bar while it hovered around 1 bar prior to the FSI rebuild. I�ve noticed that I have to drive my 911 harder to get the temp above 180. Regarding the power, definitely more power available at all rev ranges. However, I don�t know the difference from a build a Stage 1 without these options. Anyway, gapless rings have made a difference for me IMO.

In the applications where purchasers chose the updated pistons and rings the 2nd ring was used as a gapless, not the top ring. The top ring maintained the conventional design, but saw updated ring coatings, (to match Nikasil) as the conventional rings were also provided by Total Seal.

fyi - Here is the description from the options list: "All Stage I, Stage II, Street Performer, and Track Performer engines come standard with JE pistons. Our CP Pistons are developed for competition use and have proven to make more power through their competition ring pack, featuring Total Seal second rings, and a completely altered ring pack over the JE pistons. We have also built more compression ratio into these pistons, and added performance coatings to the skirts, ring lands, ring grooves, and piston crowns."

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Yes, this aligns with my post above. The Total Seal 2nd rings mentioned in the options description are the Gapless rings. Jake selected the ring profiles per case, based on what engine was being built, and what application/ use it would see. Regardless any updated combination would have a ring set comprised of Total Seal rings, and those could be conventional, gas ported, gapless, or total conform. Part of what makes the FSI engines work are these changes that were put together when considering all the other factors. In some cases where elevated power is being made even the surface finish of the cylinder was changed, so the valley of the hone would hold more oil, so the engine could be ran with elevated levels of fueling without loss of ring seal. With a change like that, other changes regarding the rings follow suite. That is just one example of what would factor in to the profiles of parts that were used together.

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So, if a piston and cylinder combo are decided and ring selection is next, which ring drives decisions for the ring set?

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All of them. No single ring is more important than the others, as each has a primary role, and several secondary roles. Ultimately you need to defer this consideration to the person who is surface finishing the cylinders, and setting running clearance. The cross hatch angles even matter, since they have an impact on ring rotation. The peak of the surface finish matters as well, since too rough might break in super fast, but will kill the rings soon. This is great for a race engine, but horrible for something that seeks longevity. If you couple that high peak with a shallow valley, it ends up as a double negative and also won't ever seal, and that creates an engine that won't even tune, so it won't even make it to the track. You can watch videos and read books all day long about this, but ultimately every engine is different, and must be treated as such. The AOS system with these engines throws another dynamic at the selections which often isn't considered. You can achieve so much ring seal that manometer readings can top 40" of water column when you really have things refined, but that can make an impact of the load based fueling and require alterations. The recommendation for initial success is to start with what is proven, and then achieve success. You can go crazy later, once you've figured out what does work. You want to avoid learning what doesn't work on your first round effort. No mater what you do for cylinders, use something that comes as a known combo of piston/ ring/ surface finish/ running clearance.