Ring Pack Thickness: Question

[BadSS]

I’m a little late to the party, especially being “that guy”. However, if you google “thin piston rings dyno” you’ll get an older speedtalk thread and a couple articles showing ring swap dyno pulls. The “Enginelab.com” article includes blow-by measurements.

Obviously there could be variables that could have come into play (as with anything you didn’t do yourself) but the numbers seem to line up with what others have said in this thread and what a reputable builder in my area had told me he had witnessed on his dyno.

[NewbVetteGuy]

Huum once read that 70 percent of friction in an engine is caused by the rings. So going to very thin modern rings of today no doubt a food thing.

I pulled a ton of data points out of an EPA paper a while back on friction:

Mechanical Friction accounts for 4%-15% of total engine losses
75% of those losses are due to rubbing friction


Mechanical Friction Break-down by Component:

• *Piston Ring Assembly: 50-68%
  *Crankshaft, bearings, & Seals: 25-35%
  *Valvetrain: 10%-20% (OHV engines only covered by study)

Oil rings alone (not the whole ring pack) are responsible for up to 8% of an entire vehicle's fuel economy (Not 8% of the engine; 8% of the entire vehicle including aero drag and tire to ground friction)

I know everyone's interested in the POWER difference but the EPA study is obviously interested in friction's impact on fuel economy, so that's what the data looks at.

A 10% reduction in engine friction would yield a fuel economy gain of 2%

Mahle claims that their 1mm/1mm/2mm ring packs reduce oil ring friction by 50% vs. their 5/64th ring packs.

Oil friction and viscosity modifiers with no chances to oil weight ratings improved fuel economy by 1% by themselves.



I wish I had the EPA study link, but I did not save it in my notes... *Fail*


Adam

[skinny z]

Now THAT'S some interesting data.

While I like power, I get an almost equal amount of satisfaction from tuning for economy.
This last 355, with a 236 @ .050" cam (COMPs 288HR) and about 10.25:1 could knock down better than 20 MPG (US) steady state highway. Certainly the OD trans and lockup converter helped but still, tuning the carb for a 16:1 lean cruise and as much spark advance as I can use (and too much in all actuality) produced some acceptable results. And that's with a fully worn out shortblock that had lost better than 20 PSI cranking compression over it's lifetime.

There's HP to be had with the thinner rings quite obviously but I hadn't considered how the reduced friction would parlay into even better fuel economy.

[289nate]

Light weight rotating assembly‘s seem to accelerate quicker but not necessarily show any benefit on the engine dyno or chassis dyno. 5 hp would be from better ring seal in my opinion. Ring wear? Proven a non factor. Maybe because it wears the bore less?

[289nate]

Light weight rotating assembly‘s seem to accelerate quicker but not necessarily show any benefit on the engine dyno or chassis dyno. Joe Sherman claimed they made less on his dyno though they were faster down there track. 5 hp would be from better ring seal sea and better over time. Maybe because it wears the bore less?o

[digger]

The data I saw from Ricardo suggested that while oil ring friction was the highest on a motored engine the top ring friction was comparable when fired as obviously gas pressure drives the ring harder into the walls radially

[swampbuggy]

Rubbing Friction was mentioned above. Everywhere in the engine that metal surfaces can come together there "Must" be oil / lubrication there to prevent damage, of course there will be a slow wear at best. If you think about the fore mentioned comment, one can realize how " Very " important the oils capabilities to battle the objectives required of it. So this brings up the 100 year old question, which oil might be the best choice Mark H.

[engineguyBill]

You will hear differing reports on how much piston rings contribute to internal engine friction, but 70 to 80% is about right. Thinner ring widths will reduce the friction to some degree but not a huge amount. I have found that ring width less than .043" does not reduce the friction by a measurable amount. Note that the difference in width between a .043" ring and a 1.00mm ring is only about .004", which is about the thickness of a human hair.
One of the benefits of reduced lateral width of current performance rings is the fact that these compression rings will seal very well with less radial thickness which results in a significant reduction in radial tension thereby reducing internal friction.

When we went from 3/32" and 5/64" to 1/16" width high performance compression rings back in the early to mid 1960's there was a very noticeable reduction in internal friction attributed to the thinner ring widths.

[PRH]

For a performance build 355 SBC shooting for 450-ish HP, I certainly wouldn’t be paying much of a premium for having an extra skinny ring pack.

[F-BIRD'88]

Gas mileage doesn't matter much when on the next block you're going to hammer on it anyway.

[rfoll]

The last three 5/64" ring sets I used have a significantly reduced radial thickness. Brands were Hastings and Mahle.

[swampbuggy]

On my current build i chose .9 mm--.9mm--2mm, If i could do it over it would be .7. .7. 2mm . Cup is right at .5 mm, actually .018 to .019 " i have one . Things at the Pro levels are constantly evolving into something new. I was told by a pretty reliable source that ( at least at one point ) the top ring face was coated with the same material that is applied to twist drills / drill bits that give them that Brass color . Mark H.

[rustbucket79]

Cup also is dry sump with crankcase vacuum. Tread lightly.

[dannobee]

For a performance build 355 SBC shooting for 450-ish HP, I certainly wouldn’t be paying much of a premium for having an extra skinny ring pack.

Very valid point. I've said for years (to the people not chasing every last hp), if your pistons are ok, just change the rings to low tension. If you have to replace the pistons anyway, run the skinniest ring package that you can find. If you're class racing in a crowded class, by all means, run the skinny stuff, but there's no sense in throwing away good parts when you're racing dial-in anyway.

[swampbuggy]

Rustbucket79, with appropriate and due respect, you kinda shot from the hip. Have you heard that old saying ? This ( my ) Engine will have ( 4 ) Scavenge sections 1.700" wide pulling vacuum in the Dry Sump Oil Pan. We are looking for 20 " , and there will be oil sprayed at the bottom of the pistons to insure that the wrist pins stay well lubricated . Mark H .