Gapless top rings and more exacting tolerances are allowing engine builders to find up to
For years piston rings were paid little attention by either racers or engine builders. They are small, fairly straightforward and on the surface would seem to have little to contribute toward finding horsepower. But that's a big mistake to make. Over a decade ago ring technology took a big evolutionary step that really contributed to power and engine durability, and I think stage two of the evolution is taking place right now.
The first time I was aware of people in the oval-track business really starting to pay attention to piston rings was somewhere around 1989-90. Really, the only reason was because we started having problems with them. It was about this time that we started pulling vacuum with the oil pump into the engine and learned that we could lessen tension on things like oil rings, pull some vacuum and increase power. In doing this you had a tendency to dry up the cylinder, which created a problem called micro-welding. That's where the piston actually transfers metal and bonds itself to the top ring. When that happens it's usually catastrophic-you lose all seal and start scuffing the cylinder.
While this was happening, a major manufacturer made a manufacturing change that none of us knew about. The change was supposed to be for the better, but it really introduced an inconsistency in the face of the ring (the surface that comes in contact with the cylinder).
The standard for quite some time has been moly-faced rings, and that's what we were using then. Normally, the ring has a channel machined into it, the moly filler is sprayed into it, and then it's ground to its finished size. There were some inconsistencies in the way this moly was applied, which created some sealing problems in addition to the problem with micro-welding. So, for quite a period of time between '89 and '90, it seemed we were either micro-welding rings or not getting a good seal.
The secret to gapless rings is a second smaller ring, called a "rail," that sits under the
So myself-and just about everybody else in the business at that time-started paying a lot of attention to piston rings where we were taking them for granted before. It became part of our build-up process at Automotive Specialists to examine every top ring all 360 degrees around under 40 power magnification. It was very costly, very time consuming and we were rejecting somewhere between 70 to 80 percent of the rings. Thankfully, the manufacturer recognized the problem and corrected it, but it took a while.
The changes that were made really helped increase the dependability of the rings, which in turn upped the durability of the race engines we were building. Now, as we learn more about what is going on inside the engine, the advances we are making are really helping out power-both in terms of reducing friction and creating more horsepower by increasing efficiencies in the combustion chamber.
Properly preparing the cylinder is an important step and an area where I feel we can still realize big gains. Every engine builder worth his salt knows the importance of using a torque plate and having the main caps torqued in place to simulate the stresses on the engine once it's bolted together. People have been doing that for years. The next step is to really zero in on cylinder wall finishes for given variables and needs. At Automotive Specialists we've looked at different types of finishes on the cylinder wall to change the Rpk and Ra values (for roughness). We've found ways to produce a deeper valley in the crosshatch pattern but still have a smooth finish. This improves oil retention on the cylinder wall without increasing friction as the ring makes contact with the cylinder wall. We've been working with a ring company and a piston company on this project, and their engineers have been very helpful. I don't mean to be an advertisement for anyone, but Total Seal and Mahle Motorsports, the companies we've been working with, have made some advancements in ring technology I'm sure you are going to want to know about.