Advances in Piston Ring Technology
Piston rings have one of the toughest jobs inside an engine. They’re slammed up and down between the ring lands thousands of times a minute, they’re subjected to searing temperatures and extreme pressures, and they’re constantly scraping back and forth against the cylinder walls. In spite of all of this, the rings are expected to seal combustion and vacuum, prevent blowby, control oil consumption, keep the cylinder walls lubricated, cool the pistons, and last but certainly not least, last almost forever (150,000 miles plus in a passenger car/light truck engine or up to 1 million miles in a heavy-duty over-the-road diesel)!
It’s a demanding list, yet most rings are up to the task and hold up pretty well — assuming the “right” rings are used for the application, the cylinders are finished properly and the rings are installed on the pistons correctly. Obviously, the ring sealing requirements of a high-revving racing engine or a hard-working diesel engine are much more demanding than those of a mild stock engine. So with that in mind, let’s look at some of the latest thinking as it applies to piston ring designs, materials and coatings.
Stock Rings

With so many late-model engines running thinner, low-tension moly-faced ductile iron and steel rings, one might think cast iron rings are fading into history. They are at the OEM level, but it looks like cast iron rings will be around for a long, long time in the aftermarket. According to several ring suppliers, there is still a very strong demand for plain cast iron rings. The main reason is that cast iron rings cost less than more durable materials — and they hold up well enough in light-duty stock rebuilt engines. Even so, plain cast iron rings can’t provide the durability of a chrome or moly-faced ring set, or a steel or ductile iron ring set that is engineered for high output,