Low tension rings

[Walt Fricke]

Builders of race engines often speak of using low tension rings. One way of measuring ring tension when assembling parts is to use a fish scale to pull the piston, with rings, through a cylinder.

All fine in theory, but how to you adjust ring tension? Rings are kind of brittle, and I don't think you can just squeeze them some before (or after) installing. So do you have to purchase low tension rings? I don't recall seeing that as an option in a ring manufacturers catalog.

[reclino]

I bet the safest way would be to call Total Seal and ask them if they could make you low tension rings. https://m.youtube.com/watch?v=Q0h9AUnJPmw

[Trackrash]

I remember this was written up in Hot Rod many years ago. Basically they took every available ring and tested it.

I wonder if a used, but inspec ring would have less tension.

I would also be interested in what difference it makes.

That opens a can of worms, like is thinner oil worth the trade off for less friction, but also quicker engine wear? I bet no engine builder who knows the answers will chime in.

[Ollies930]

Low tension rings are manufactured as such. You cannot convert a standard tension ring to a low tension one. And really you are talking about the oil scraper assembly, not the top two rings. There is a little bit of gain in hp and since there is less friction, there is also less heat. But in the grand scheme of things, not worth the effort unless you are in the process of putting rings into your engine and weighing your options. Total Seal has different options available in certain dimensions, or you could custom order a set made just for you.

[dannobee]

ALL of the rings matter, not just the oil control rings. The thinner the rings, the better they seal against the bore and the less friction they have.
Even the factories are on board with skinny rings. Reduced flutter, better sealing and lower frictional losses.

And to let out a dirty little secret, some racers leave out the second compression ring entirely and rely on only the top ring to seal. This, combined with a low tension oil control ring package can be worth over 3hp per cylinder. In a properly machined and clearance cylinder, you would never notice a difference. Obviously if the bore goes oval or scores, oil consumption and sealing suffer, but at that point it needed to be torn down anyway.

Another factoid that added a few hp was to break in the engine on the dyno, then disassemble and rehone the cylinders, then reassemble with the old, already seated rings. We theorized that the rehone reduced ring friction by more oil sticking to the cylinder walls, but in any case it did something and we knew that it worked. When you're in a rule restricted class, every little bit helps.

[Mr Beau]

https://www.enginelabs.com/engine-tech/is-thin-really-in-ring-thicknesses-put-to-the-test-on-the-dyno/

[911pcars]

The piston ring/cylinder interface represents the greatest amount of frictional losses in a high revving engine. The trick is to reduce that friction with trick rings or other designs while also able to maintain combustion chamber sealing at the same time. I recalll Honda tried using very close fitting pistons w/o rings in an attempt to reduce frictional losses. At 18,000 rpm, it counts. Alas, it didn’t work as planned.

Sherwood