Closing the Ring Gap
Engine Builders Creating Maximum Power By Managing Ring Gaps Through Proven TechnologiesBy Scott Gabrielson Ask any successful engine builder in NHRA or NASCAR competition about his recommended end gaps for the top and second piston rings and you'll probably hear "no comment." And for good reason. It's impossible to overstate the importance of running with exactly the right end gap if you're hoping to create a perfect combustion seal over the course of a race, be it a quarter-mile pass at an NHRA track or a 500-mile superspeedway event. The fundamental principal behind maximum ring performance and efficiency in a racing engine is sealing all of the compression with the top ring. This fact is born out through the proven pressure dynamics between the top and second rings: The top ringis sealed against the cylinder wall and the bottom of the ring groove by the pressure differential created during the piston's combustion cycle. As pressure increases above the ring and between the ring's inside diameter and the piston groove, the ring is forced downward and outward, creating a tight seal over a wide range of engine rpm. Even though it is often called a "compression" ring, the second ringin a racing engine should not be counted on to seal combustion gasses, but simply to scrape excess oil from the cylinder walls. In order to utilize the second ring for additional combustion sealing, it is necessary to virtually eliminate the ring's end gap. This, however, is disastrous from a compression standpoint: With a small (or no) second-ring end gap, combustion gases become trapped between the second and top rings. As the piston moves through its power stroke, these gases will lift the top ring off its land, causing extreme loss of seal and promoting ring flutter. The secret to more power, therefore, lies in keeping the combustion gases above the top ring. And although many engine builders in NHRA and Winston Cup competition won't share their secrets regarding top ring clearances and end gaps, the optimum approach can be found simply by relying on a world-class ring supplier that partners with winning teams. Fact: There are No Shortcuts Needless to say, the top ring in a racing engine is required to withstand considerable abuse, in spite of the fact that the rings typically are becoming thinner and lighter to minimize frictional horsepower loss.
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The best top-ring technology in today's ultra-high-horsepower engines features a one-piece design utilizing high-strength ductile iron with a plasma-moly facing material. The ductile iron material provides the strength and resistance to detonation required in a racing engine. The plasma-moly facing has a high melting point to resist scuffing, and a controlled application process that enhances ring lubrication. Some manufacturers use an advanced plasma-moly formulation that also has higher bonding strength to resist flaking and ensure extended face life. Of course, the optimal top-ring end gap for maximum sealing performance is near zero when the engine is at normal operating temperature. The trick comes in determining the best installedring gap, which, as the engine heats up, will close to provide a complete seal. The correct installed gap is a function of the bore size, piston, ring groove location and operating temperature at the top ring. Are Gaps Really Necessary? Is it possible to achieve maximum top-ring sealing with a ring that has zero installed end gap? Not as this technology exists today. One recent zero-gap-type top ring design is comprised of two individual pieces a high strength ring with a separate steel oil rail-type piece sitting within a counterbore. These pieces are positioned so that their gaps are staggered, thus the claim that they have no installed gap. This approach offers several concerns: Because the ring is in fact two pieces, both must somehow maintain identical contact with the bore in order to seal properly. If the pieces act independent of one another which is likely in a high-rpm, high-heat environment ring face contact would not be consistent and sealing performance would suffer. In addition, if the two pieces perform independently, their respective gaps could become aligned, creating a wide escape path for combustion gases. In truth, the development of a zero-gap-type top ring begs the question: Why would you then need a secondring that has zero installed gap? The latter technology, which has been available for several years, employs a similar two-piece approach. This configuration has received exhaustive study by many of the best-known engine builders in NHRA and NASCAR competition, virtually all of whom have found that this type of second ring offers no performance advantage. The reason, again, is the potential for trapped gases between the top and second ring to lift the top ring off its land. The development of a top ring with zero installed gap, regardless of its manufacturer's claims, is an acknowledgement that the combustion seal in a racing engine must be at the top ring. Why do these zero-gap-type rings exist? Because it's a free market, and manufacturers can create and promote their ideas as they wish. The question, however, is if this technology were really valuable, why wouldn't the world's largest ring and engine manufacturers offer it? The answer is simple: real-world testing by these manufacturers
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and racing teams -- shows that this approach is not consistent with good ring dynamics and engine performance. At the very least, you owe it to yourself to ask for certifiable test results from any manufacturer that claims to have a "new" solution to combustion sealing. Ask successful performance engine builders whose rings they use in their racing motors. What's Right for Your Engines? Our company and others offer detailed ring gap specifications/recommendations for a full range of applications. These recommendations are developed through input from thousands of customers and real-world situations. If you rely on piston rings from a major, global manufacturer that has an extensive presence in NHRA and NASCAR competition, you can be confident that the materials and designs you use represent the best technologies available. When it comes to choosing the right end gaps for the top and second rings in your engines, use the manufacturer's recommendations as your guide. Again, the key objective is to achieve near-zero top ring end gap under real-world (racing) operating temperatures. If you're looking for short-cuts for more power through a new ring technology, they don't exist. The best engine builders focus, instead, on perfecting the fundamentals of racing-style rings choosing the right materials from the best-known manufacturers and adapting these technologies to their engines. You can and should do the same. Scott Gabrielson is Sealed Power piston ring application engineer for Federal-Mogul Corporation. He works with dozens of racing teams in identifying the best ring technologies for championship performance.
They don't like Total-Seals but I am going to give them a whirl anyways!
Instruction sheet with rings will give specs for forced induction.
