Piston ring thickness

[fekbmax]

Ok, really what's the advantage of the new modern mm ring packs compared to the 1/16" ring packs. Tit for tat. Low tension,  standard tension,  what ever. How much is hp is the mm ring pack worth over the 1/16" ring packs.

[RustyCrankshaft]

I think 2 of the major ones are less bore wear and less friction. It's pretty noticeable on assembly when you check the rotating torque with all 8 pistons in the block on the same type of engine with old skool ring packs vs modern metric ring packs (Even standard tension). I've noticed a lot less bore wear with narrow rings. I've torn down a lot of 90's 460's in trucks at work with 200k+ miles and the bores are still fairly straight and with about half the wear I saw with the older 460's. Same kind of trucks, same fleet, same type of use so I think it's a fair real-world comparison.

I've also read a lot of SAE and OEM level stuff talking about sealing and ring control, etc. Not sure how much of that directly applies to a high performance/race engine but some of it certainly carries over.

Someone who knows a lot more than I do will be along shortly to further expand.

[blykins]

It's well worthwhile.

There was a test done somewhere, can't remember where it was, but going from a thicker old school ring pack to a 1.5/1.5/3mm ring pack resulted in an 8-10 hp gain. 

As mentioned above, it reduces friction, and it should help ring seal, considering the CSA of the ring is much smaller, but the same "force" is applied to it. 

I did a 351C with 1mm/1mm/2mm rings and after the engine was broken in and rings were seated, with plugs out and valvetrain unhooked, the rotating assembly rolled over with 7 lb-ft.

[RustyCrankshaft]

I did a 351C with 1mm/1mm/2mm rings and after the engine was broken in and rings were seated, with plugs out and valvetrain unhooked, the rotating assembly rolled over with 7 lb-ft.

I usually check how much torque it takes to roll the shortblock over and then again after full assembly (plugs out) and the first 1.5/1.5/3mm engine I did I shocked at the difference. Even prior to break in the shortblock the difference is noticeable. On that first one I thought I screwed up somehow. Went back and made sure I didn't accidentally order low tension rings or something.

[My427stang]

So I have had experience with a sample size of zero, but I am a research hound and cheap as hell LOL

Both Brent and Barry pushed info to me, as well as every piston ring manufacturer and article on the net I can find agree, there really is no reason when swapping pistons to stay with the thicker rings.  Brent referenced a Hot Rod or PHR test that compared 5/64 to 1.3mm, on a relatively small bore and short stroke SBC, it gained about 10 HP.  Longer stroke and bigger bore would gain more as there is more internal friction

The reason this is doable is that ring material got better and allows a thinner ring, essentially wire not cast.  Making them thinner is the same concept that we went 1/16 from 5/64.  My conservative answer is go 1.5/1.5/3.0 with a good torque plate hone and don't look back, which I am doing for the 461CJ  I have in the works

However, I cannot even really find a downside with good machining for even thinner, an that's why on my own 461 EFI motor, I ordered a set of Mahle 1.0/1.0/2.0 rings with Autotec 4032 pistons. 

I believe they require a straighter cylinder, but I am not even sure that is true, the ring should follow better and have a better contact pressure, however, what I don't know is if the ring would lose temper faster than a thick ring with a tapered or misshapen cylinder.  Logic says yes, because if it follows the surface more accurately where a thick ring will ride over.  If that is true, the thin ring  may work harder.  All that does is require good machining and adequate cylinder wall.

We will soon see on my pair of relatively low-po 461s (compared to the drag racers)

[machoneman]

Anyone know how many hp that SBC developed in that thin ring test?

Point is, if it was a 400 hp engine, gaining 10 hp with thinner rings, that's a 2.5% gain. I'll venture that percentage could be used across higher and lower hp'ed engines (600 hp x 2.5% = 15 hp gain). Nothing to sneeze at for sure.

[gt350hr]

    Less ring drag certainly equals more HP.  The change from 1/16th ( .0625) to 1.5mm (.0581) also gets a reduced "radial" width which is where the lesser drag comes from. Conventional ,"fractional size" rings have a radial depth according to SAE ( Society of Automotive Engineers) "D wall" specifications. That spec is bore diameter divided by 22. So take a 4.250 bore for example and the "D wall" radial depth would be .193 ( on average) and a "Metric" ring would have a "non SAE" radial depth of .160 ( average among manufacturers) . That .033 make a noticeable drag reduction but the MAJOR reduction is from the oil ring going from 3/16ths to 3 mm ( .188 down to .119) in height. The radial drops from .187-.192 ( average again) to .145-.155 ( average). That is HUGE as far as reduction in ring drag. Thinner rings like 1.2mm , .043, 1.0 mm , .9,.8,.7, and the latest .5mm ( I don't know HOW they can seal but they do) rings used in Nascar lower the drag even more. Not ALL of these rings are practical for "our" use , but they are "out there"."Most" if not all current V8 engines are using metric rings for their low drag and ability to go 100,000 or more miles.
   All this makes me feel old since 5/64 ths was the "norm" and 1/16th was "race" when I was growing up.
       Randy

[Falcon67]

I use the 1.5/1.5/3mm in my 351Cs and haven't noticed any issues.  I can say that the 3.5x4.03 bore using light weight Probe piston 1.5/3mm engine made easily 40 more HP than the older TRW forged 5/16 3.5x4.03 short block. Easily.  Maybe more - switching short blocks dropped the car from 7.2x in the 1/8 to 7.6xs, loss of 4~5 MPH

[WerbyFord]

Sep 2017 Hot Rod dynode a 377 scrub 4.155 x 3.480, picked up about 5 ftlb across the board with 1.2 1.2 3.0mm ring pack, out of about 450 ftlb level.

Worth it? To me that would depend on bang for the buck - and longevity.
5 ftlb sounds kinda low vs what we are talking about here.

Thing is, when you get up to 1.5mm that's .060", awful close to the old 1/16" "thin race" rings.

Jul-Aug 2009 Chev HP says low-tension gapless rings (they don't give thickness) were worth 10hp on a 570hp strocker 348 W motor.

[fekbmax]

Thanks guys for all the info. I have an opportunity on a great deal on some JE pistons with the 1/16th low tension ring pack, .990 pins, that's been setting on a friends shelf for about 4 years. Probably could save myself close to 5 bills over some custom race tech's with rings and pins. I'll have to think it over though cause I want all the HP and any benefits I can get.
You guys have given me food for thought most certainly. 
Thanks again.

[gt350hr]

   Werby ,
       It's sad but often magazine articles are skewed toward the advertiser ( or free source) of a product.  While the HP increase IS valid what isn't mentioned is what the power is after a month or three . I witnessed a test years ago at a particular Nascar shop when they tested the gapless top ring. It did indeed show an instant increase to which the shop owner said "gas up the dyno and cycle it for 24 hours so we can see if the power stays". Dyno records showed the power fell to "regular gap type ring power levels after the second hour of dyno cycles and were exactly the same as the gap type ring after the grueling test. The extra cost just wasn't worth the momentary gain.
    Randy

[WerbyFord]

   Werby ,
       It's sad but often magazine articles are skewed toward the advertiser ( or free source) of a product.  While the HP increase IS valid what isn't mentioned is what the power is after a month or three . I witnessed a test years ago at a particular Nascar shop when they tested the gapless top ring. It did indeed show an instant increase to which the shop owner said "gas up the dyno and cycle it for 24 hours so we can see if the power stays". Dyno records shwed the power fell to "regular gap type ring power levels after the second hour of dyno cycles and were exactly the same as the gap type ring after the grueling test. The extra cost just wasn't worth the momentary gain.
    Randy

Thanks Randy nice tip. I guess I wonder if thin rings do the same?

Our 2000 Mustang 281cid ran its best at the strip its first time out, after that it was always a tenth or so slower. Never matched that 1st ET or MPH again. Or it could have been WerbysWife letting carbon build up in there so the automatic knock-retard kicked in.....

[Kirk Morgan]

We played with the oil rings also until the engine became a smoke machine. Then added a little more tension. This was on my 390 stock eliminator.

Kirk

[gt350hr]

 Werby ,
     The ring in question ( both gap and gapless) was 1.2mm or .047 in axial height.  Thinner rings That are sealed up) will always have less parasitic drag than their thicker counterparts. It would only change as they age as the wear begins to affect them sooner than a thick ring.
    Randy