Years ago, when we were running TZ750 two-strokes in the Daytona 200, high detergency oil was preferred over castor-based oil. The issue was gumming and sticking of the single piston ring over that long haul.

Why not just move the ring a couple of millimeters down the piston to where conditions are cooler? The problem is that the unburned air-fuel mixture that is packed into the space between the piston’s top land and the cylinder wall, and above and behind the ring in its groove, is a significant amount – 1 – 2% of the whole charge.

How can this be? Because it’s packed in there by combustion pressure. It can’t burn in the crevice space because it’s surrounded by cooler metal. As it outgases during the power stroke and into the exhaust stroke, if it does burn it is far too late in the stroke to contribute to peak pressure.



On an RG500 Suzuki race piston I have here, the ring is only 3 mm down from the crown.

The result is that in four-stroke race engines as well, the top ring is pushed as high as oil detergency and dispersant additives will allow – to as little as 1/8 of an inch down from the piston crown.

OK, but surely all these four-strokes have piston cooling oil jets. Don’t they banish gumming or sticking?

Oil jets do a good job of cooling the piston crown and the highly-stressed wristpin bosses, but the top ring and the tender top land really need another source of cooling.

Persons of good sense looked at this and said, “Why hasn’t anyone ever tried making the top ring out of something that conducts heat better than iron, steel, or titanium (as used in super-rpm applications)?

Copper conducts heat several times better than conventional ring materials, but you don’t usually associate copper with high stress applications – like hammering around NASCAR ovals for hundreds of hot miles.

Fortunately, metallurgy already had something to offer. We know that aluminum can be given remarkable strength by alloying it with materials that “age-harden” – once cooled, certain alloying elements can form hard intermetallics that precipitate within the material. They act as “keys” that make it much more difficult for layers of atoms in metal crystals to slide over each other under stress. This is precipitation hardening.

Metals are crystalline by nature, and once cooled consist of myriad tiny crystals (grains) held together by less-well-organized intergranular zones.

Copper can be precipitation-hardened as well. Specialized copper, nickel, silicon alloys can be heat-treated, cold-worked and aged to give a material that combines remarkable strength with high thermal (and electrical) conductivity. The names “Toughmet” and “Performet” identify such materials from an outfit called Materion.

The claim is that by rapidly conducting heat out of the otherwise very hot-running top ring land, to the cooler cylinder wall, high conductivity rings of this kind can reduce top land temperature by “up to 30C (54 degrees F),” thereby increasing its strength and reliability. The lower temperature also makes lubricant gumming and sticking less likely. This piston ring transfers heat to the cylinder wall especially well because of the very thin lubricant film supporting it.

To make these materials able to slide against the cylinder wall and ring groove surfaces, they must be plated.

As you’ve surely been suspecting, all this precise processing raises the price of a V8 set of such rings to 5 to 10 times that of conventional rings.

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