NDH2O

Yeah we will see how they hold up to the nitrous this season,

MILD THUNDER

iTrader: (3)

I agree. The whole gapless thing sounds great, and at first thought, would lead you to believe that not having a top ring gap, can only help reduce psi loss, compared to whats lost , thru a conventional ring gap.

But how big of a gap are we talking about. Lets say a 540ci, with a 4.500 bore. Even in a blown application, and say .027 gap cold. We know the gap gets smaller as the piston warms up. How much, idk, lets say it shrinks to .010. Then , you only have a small portion of this gap, between the bore and the piston exposed. Depending on the piston width and bore clearance.

Point being, this gap under running conditions, is very minimal. Probably why like you said, the power gains have been proven to come from ring tension, thickness, cylinder honing procedure, and block/cylinder rigidity . If ring sealing for max power was my goal, id be looking at a nice solid merlin , dart style block with thick cylinders that wont distort , good machine work and assembly. Seems like those things,, are more important than whether the ring has a gap, or doesnt. Both designs seem to work well, if all those things are considered, and both wont work well if they arent.

powermizer

I do have to agree on blocks. I just got my big m back from my friend who is a machinist and he said that with the deck plates on it only took .0003 to clean up. That is impressive being a gen 5 I had him do before was close to .002 out with deck plates on.

Panther

Maybe I'm old school but I'm not quite sold on the thin metric rings just yet. I know they're supposed to free up HP but on some of the big bore engines I've torn down with metric rings, the sealing wasn't the greatest and they were oil burners. Could have been the skirt design on those engines (very short) as well but I'm not sold just yet.

Panther

My machinist also had similar feedback and they told me that they burn through a lot more stones with the Dart blocks as the metal is harder to cut and it takes a lot longer to machine.

airjunky

iTrader: (2)

Some of gm and hondas short skirt , low tension designs had some issues with piston slap and oil consumption for sure but alot of the engine guys swear thats where the internal friction gains are made or lost. Finding that balance . I remember hearing some of Lingenfelters stroker motors on cold start, make some alarming amounts of piston slap. But they made huge power and stayed together.
Honda is back to thinner low friction rings , and there have been some problems with them having gaps line up and the rings not seating properly , then what happens is the oil comes up and cokes up in the ring lands and really causes sealing issues. Wouldnt anticipate that in marine enviroment with more frequent oil changes most see.
I would trade some oil consumption , minor of course , for a handful of free horsepower personally.

Knot 4 Me

Subaru uses low tension rings as well and has had problems with oil consumption, especially with their 2.5L boxer that calls for 0W20 synthetic. My wife has one in her '15 Legacy. The oil consumption problem was supposed to be fixed for her model year but dealerships are performing oil consumption tests and putting long-blocks in '15's and up as well as the older models. Wife's car uses 1 qt. 0W20 M1 every 5K. I've not owned a new car that touched a drop of oil since my '94 Bonneville that had bad valve guide seals from new. I run 5W30 instead of 5W20 in my Ford trucks (5.4L and now 5.0L) but not sure how the Subaru boxer engine would take the heavier oil. Wife's old '10 Accord didn't use oil running 5W20 and neither does my son's '16 Wrangler JK.

Cole2534

iTrader: (1)

An aside about Mahle-

Another forum I visit has a frequent poster that works for Mahle. I'm not sure of his exact title, but the way he discusses how they build and gauge pistons is incredible. Holding 0.0001" dims on huge production runs, designing pistons with a profile such that the piston's deflection works in their favor, all sorts of extremely intricate stuff. Most of the info is relatively sanitized but reading through all of it gets you a clear message- Mahle runs one hell of a production facility.

Post #6
http://www.practicalmachinist.com/vb...istons-167754/

GrannySShifting

If you talk to good ring guys at Total Seal, they will tell you not to use gapless rings in anything other than a race car that sees just WOT. Any engine vacuum/part throttle they will oil pretty damn good

MER Performance

Plasma moly rings are ok, but the application of the moly has changed and is subject to breaking off. I use a moly ring from CP I believe comes from total seal. This I use on a NA application. This may include a Napier 2 nd and low tension low control.
Supercharged I use a Hell Fire on lower HP builds and a Gas Nitrided steel top ring on the higher HP. This will include a Napier and low tension oil control. Cylinder finish changes with each change of ring pack. Long ago I used a gapless 2 nd ring, I was steered away from that, by CP engineer, he explained what happened and how important opening up the 2 nd ring end gap was. We talked about gapless top rings, there is a very critical fit with those two rings, if one thing goes wrong with the fit or the tune, it's all over with. The 2 nd ring doesn't seal compression, nor is it a back up. The Napier 2 nd is actually wiping the oil from the cylinder wall.
If the combustions pressures build between top and second ring, both rings become pissed off and ring seal is lost.
Gas porting aids in ring seal, but in endurance applications, prematurely wears rings and cylinders.