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.
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.
The ring manufacturers have been using profilometers for years to measure Rpk and Ra (surface roughness of materials). We don’t even have one yet, but I believe the time is soon coming when it’s going to be a necessary piece of equipment in every engine builder’s shop. The profilometer has shown us that different alloys used in different engine blocks—say a production GM block to an aftermarket block—will respond better to different honing patterns. That’s not to say that the same honing procedure won’t work, but I’m convinced that there are some advantages to be had by varying the process depending on the material, its hardness, alloy content and some other things. Ring seal has become a science in itself. If you want to take that next step in power, it’s something engine builders are going to have to be aware of.
In the near future I think we will start seeing—where it’s legal—different types of cylinder wall liners. The Nikisil liner has been around for a few years, and I think you are going to see similar things involved in our industry. There are a number of processes in the works now that I think are going to make liners more practical and affordable for the average racer. Even today, aluminum block engines have a sleeve you can remove and replace pretty readily, so we may see that in those types of engines first. I can definitely see somebody within the industry offering a piston/ring/cylinder package that will be worth some power. It’s probably already taking place in Formula 1, but the way things are going I don’t think it will be too long before it’s available—and affordable—all the way down to maybe the touring series level.
So what does this have to do with the Saturday-night racer? Plenty.
Manufacturers are able to hold both pistons and rings to much tighter tolerances, so simply doing a good job of cylinder preparation—good, straight, round cylinders—is going to produce power. On top of that, ring manufacturers are very free with the knowledge they are gaining in honing procedures, and they are usually very willing to teach you what they spent a lot of money and effort to discover.
A lot of the gains these days are coming from improved fit between the ring and the piston. This is a result of both ring and piston manufacturers learning how to produce their products to tighter tolerances. The CNC technology available today makes it possible for the ring lands to be exceptionally flat, almost zero variation all the way around, which is absolutely critical. That contributed to a lot of the problems we were having years ago, but we didn’t realize it. It used to be only the Winston Cup teams could afford the processes it took to create nearly perfect pistons, but that technology is beginning to trickle down and you can find that level of perfection on some pistons marketed to the Saturday-night racer. One of the companies we have found producing pistons with exceptionally flat ring lands is Mahle Motorsports. Again, I don’t mean to be an advertiser for anyone; I’m just trying to pass on some of the things I’ve learned.
I believe engine builders have contributed to the problems with uneven ring lands by machining on the pistons after we got them. The piston manufacturers have found out that the ring groove needs to be the last machining operation performed on the piston. If we get a piston and it’s got perfectly flat ring grooves, then we mock the engine up and realize we need another .080 valve clearance, we’re going to put that thing in a chuck and cut that .080 out of the valve relief. There’s a chance we’ve just done some damage to the ring groove. You are generating heat that’s inconsistent with what the piston is going to see in the engine, and I’m sure that machining it contributes to some of the inconsistencies in the ring grooves.
I can’t speak for other engine builders, and the only thing we take to the bank is what we know for ourselves, but on a 570hp engine I’ve seen gains of six to eight hp with absolutely no other change other than switching out the piston/ring package. It was just improved ring seal: lower tolerance rings, precise ring grooves in the pistons and us not screwing around with the pistons after we got them. Even when I was assembling the short block it was obvious that it required less force to turn the rotating assembly.
The two big factors when it comes to piston/ring/cylinder wall fit are friction and efficiency. Friction is obvious, and reducing it is absolutely vital on low horsepower engines. Once I was testing a 400hp engine on the dyno. After a couple of pulls I dropped the pan and pulled the heads so I could get the pistons out. I pulled off the second ring, bolted everything back up and ran it on the dyno again. The engine gained five hp right there, so that tells you how much friction just that second ring can generate.
Efficiency is the other factor. On a naturally aspirated engine, you are depending on the vacuum created by the piston travelling to the bottom of the cylinder to pull in the air/fuel charge. The better ring seal you achieve, the more vacuum you are going to pull, and the more air/fuel charge you are going to have available in the combustion space to produce power. It’s that simple. It isn’t a matter of doing anything extravagant, it’s simply a matter of having everything spot on.
A Second Opinion ...
Matt Hartford is an engineer with Total Seal Piston Rings and someone I’ve worked with quite a bit while experimenting with pistons, rings and honing processes. Matt can explain the advances in ring technology better than I ever could, so I asked him to help us out with that topic:
At Total Seal we’ve done a lot of work with Winston Cup and other top teams to develop ring packages with the tightest tolerances possible. The CNC technology out there now allows piston manufacturers to hold their land flatness to within a micron (.000040 of an inch). Old-style rings were only able to hold thickness variation to .0005 or .001. Now, we’ve developed technology to hold ring thickness, parallelism and flatness to plus or minus .000050 to take advantage of the increased flatness of the piston lands. Having a consistent radial thickness (the distance from the ring’s id to its od) is also vital. It takes five separate machines to get our rings to this level, but that’s about all I can tell you.
For engine builders, using a flatter, smoother ring is important because the flatter the ring seals to the piston the more blow-by it can eliminate. Blow-by is wasted efficiency, so the more things you can do to eliminate it the better.
When we’re talking about efficiency, back clearance—the space between the inside of the ring and the piston as the ring sits in the groove—is also important. The less you have the better. Think about it this way: Beginning at top-dead center the intake valve opens, the piston moves down the bore and the negative pressure created in the cylinder draws atmosphere through the carburetor. But before that can happen the negative space above the piston as well as the space between the ring and the piston groove must be filled with the negative pressure. The smaller that space the less time it takes for that area to fill and the piston can start doing its job.
As you move to the compression stroke, as the piston and ring begin compressing the air/fuel charge it also has to compress everything along the sides of the piston down to the top ring and the backspace area between the inside of the ring and the groove. Of course that’s a quench area, so when the spark plug fires nothing in that area burns. It’s wasted energy. So the tighter you can hold the back clearance, the more efficiency you can have on both the intake and compression stroke.
Total Seal’s top-level rings are called “Diamond Finished.” They are held to extremely tight tolerances and can have our proprietary anti-friction coating. We also have a variety of basecoating available to maximize performance depending on the hardness of the material used in the engine block.
An old block that you pull out of a junkyard that people have used in the lower levels of racing for years and years requires a different basecoating on the rings than a Winston Cup block, which is a very hard block. So depending on what the block is, we know what it needs for a ring. Now granted, we don’t tell people what that is—the Cup guys don’t even know what they are getting. They just know it works and they can see the results on the dyno. The rest they leave up to us.
When an engine builder switches from old-style rings to top-level rings, like our Diamond Finished line, we normally see gains in horsepower around three to five percent. No matter what else you are running, tighter ring tolerances are going to help you because you are going to have a higher efficiency on the intake stroke. The whole thing we are looking for on ring seal is how much atmosphere you are able to pull into the engine. Anybody can seal an engine on the compression stroke because you have all that gas pressure behind the ring holding it to the cylinder wall. The trick is getting a good ring seal when the piston is going down and trying to pull all that atmosphere through the carburetor. It doesn’t matter how good your flow numbers are in your head or how much air speed you are getting on the flow bench, if your piston/ring package can’t get good vacuum you are wasting that head’s potential and you aren’t making all the horsepower that’s available.
The Diamond Finished series goes for about $600. This set isn’t cheap, but they are gaining popularity in a lot of different series. For the non-professional racer who doesn’t have the resources to buy a $600 set of rings or $2,000 worth of pistons to take advantage of them, the technology used to create the Diamond Finished series rings has also helped improve the quality of the sportsman-level rings. I would recommend a gapless top ring set. They are going to be moly-faced in either a two- or three-ring setup. Predominately, you are going to see this in a three-ring engine, because now you are getting into a ring set that’s under $200 and this is a racer who probably also isn’t investing in Winston Cup-level pistons, either. An off-the-shelf piston from some of the better manufacturers is a great product for his needs, but it isn’t held to the same tolerances as a Winston Cup piston, so he doesn’t need a $600 set of rings. A good rule of thumb is you should expect to invest in rings about 30 percent of the cost of your pistons. So if you have a $600 set of pistons, you don’t need a $600 set of rings.
Just by switching to a gapless set of top rings you are going to see substantial horsepower gains, probably in the range of three to five percent. That comes both from reducing friction and creating more power. A typical three-ring set of rings costs roughly $130. A gapless top-ring set costs approximately $180, so for $50 more you are going to see around a five percent gain in horsepower. That’s about the cheapest horsepower you are ever going to buy, plus it will make the engine live longer because it’s not putting heat down into the crankcase. That’s something anybody can do.
To make the most of better rings you need to be using the correct honing procedures. Just like with the Winston Cup guys, all you have to do is call your ring manufacturer to get good tech help on the best honing pattern for the block and your rings. I can’t speak for other companies, but no matter what rings you are using the tech guys at Total Seal with try to help you out. Good luck and good racing!
