Rings are rings right? Wrong! In addition to thickness and diameter, there are several different ring materials, styles, and coatings available to maximize performance in a variety of engine environments.
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Not all that long ago, piston rings were all the same. They were heavy, thick, and you could have any material you wanted – as long as it was cast iron. Today, the performance engine builder has a broad span of material choices when it comes to piston ring materials and finishes. This is a direct result of the push for stronger ring materials faced with surviving the harsh environment of higher cylinder temperatures and pressures.
JE offers a variety of piston ring materials, styles, and coatings all built around different performance applications. If an off-the-shelf ring won’t cut it, custom ring services are also available such as grinding, lapping, and dyke cutting.Before we delve into materials, the responsibilities of a piston ring must be reviewed. While sealing combustion pressure is the obvious goal, an equally important function is to transfer heat from the piston to the cylinder wall. As rings become thinner, this heat transfer function becomes even more critical. Third, the rings must minimize the amount of oil that enters the combustion space. While many enthusiasts think that the second ring’s main task is a backup to sealing cylinder pressure, the reality is that 80 percent of its intended function is oil control to sweep up the remaining oil from the cylinder wall not removed by the oil ring.
For a performance engine, the piston buyer is faced not only with choosing the proper piston configuration and compression ratio, but also with selecting an optimized ring package. Much of this selection process is dictated by how the engine will be used. This must begin with the selection of the proper ring material. Ring widths and design can be chosen once the material has been finalized.
The current JE piston catalog lists a multitude of ring materials which may appear at first to be a daunting challenge. The first is carbon steel, which is a much more malleable material than cast iron, is able to handle higher temperatures without losing temper, and is better able to withstand bouts with detonation. Cast iron, by nature is very brittle and therefore not as strong as gas-hardened forged steel. Gas nitride top rings perform so well in so many different applications that even the OE now spends the extra money for this ring material for production engines.
While this sounds like a generic use material, carbon steel is also a great selection for high cylinder pressure applications like nitrous, turbo, supercharged, and high-rpm engines.
Steel nitrided top rings are an excellent ring in terms of durabilty and strength. They are formed from forged steel for strength and ductility, and the nitriding process makes them extremely hard and detonation resistant.Chrome faced rings were a popular option a few years back, but now have also succumbed to progress and are rarely employed in modern performance engines. The problem with many chrome facings was that they were extremely hard and difficult to break in properly and often suffered from flaking or cracking when exposed to detonation. Most dirt circle track applications have now converted to steel nitride ring packages. Some steel nitride rings are offered with a plasma molybdenum coating in addition to gas nitride.
Steel nitride top rings are a great choice for street performance applications, but may not be necessary from a cost standpoint for every engine. JE offers other options for the cost-conscientious engine builder. Hardened ductile iron is a great choice for serious street engines that do not demand the high temperature tolerance compatibility of a race engine. Ductile iron is a step up from typical cast iron with magnesium added to the grey cast iron to improve ductility –making this material more apt to bend instead of break.
Grey iron rings were the staple for many years. While more than adequate for a second ring in street applications, their brittle nature makes them sub par for outright performance in a top-ring setting.Some engine builders prefer a slightly older technology that they’ve had success with in the past including carbon steel rings with a harder chrome face (listed in the catalog as JC and JXC Series rings). This process is compatible with all cylinder bore materials except Nikasil.
Ductile iron is roughly twice the tensile strength of grey iron and tends to bend instead of breaking when subjected to stress. This makes it a great top ring selection when price is a consideration. Most often, ductile iron rings are offered with a plasma molybdenum (moly) face coating to make them more compatible with iron cylinders.
JE’s Premium Race Series is a great example of a ductile iron top ring that uses the more modern plasma-moly inlay technology. The plasma moly application produces a somewhat porous yet extremely hard, wear-resistant surface that retains oil and improves lubrication while also reducing friction. The plasma is created by spraying an alloyed powder containing Chromium, Molybdenum, and Nickel along with other trace elements into a small channel in the ring’s face. Using extreme heat, this powdered metal turns into a molten spray that offers superior adhesion characteristics which reduce the potential for flaking. This added porosity also improves initial ring break-in, reducing the time it takes for the rings to optimize sealing.
Back in the days of musclecars, a 5/64th inch ring thickness was state of the art. With modern materials, coatings and profiling, thinner rings have become the new staple. Shown is a 1mm top ring next to a well-worn dime.The discussion up to now has focused on the top ring. The second ring is subjected to far less heat and pressure than its top-rung brother and therefore does not demand as expensive a material. As an example, the Plasma Moly ring package listed in the JE ring chart is an excellent ring package specifying a carbon steel nitride top ring with a ductile iron second. A less expensive version of that combination would be the Sportsman Series ring package that specs a plasma-sprayed ductile iron top ring combined with a grey iron second ring.
Oil ring packages tend to be less cumbersome in terms of materials with most options offering carbon steel for the two sealing rings. The expander design may change but the most important question for oil rings is establishing overall tension based on how the engine will be deployed.
Once you’ve made your ring material selections, you can move on to the next level of decision making in terms of top and second ring design, face styles, radial thickness and perhaps any special treatments such as lapping and/or ultra or critical finish steps. This entire process is all aimed at optimizing ring seal and capturing all the cylinder pressure within the combustion space where it can do the most good.
The quest for more engine efficiency has auto manufacturers adopting thinner rings for greater efficiency when it comes to the family sedan. MAHLE has also embraced this technology, and much more in its motorsports division.
MAHLE Motorsports adopted a new thinner ring technology for performance and racing applications a few years back. The next stage for MAHLE is to educate racers about how these unique rings function and spell out the benefits for their next engine project.
We asked Joe Maylish, program manager for the MAHLE North American motorsports division, if material advancements sparked the new narrow rings compared to the thicker rings that have been the norm in the high-performance world for many years. His response is, “Yes, and more.”
“Material is one of the factors,” says Maylish. “MAHLE produces a huge volume of piston rings per year for automotive manufacturers and other applications. The volume of specialized raw materials we use with rings on the OEM side allows us to also engineer and manufacture effective rings for motorsports with an extension of that cutting-edge technology.”
Typically, piston rings can be constructed with different raw materials such as alloys of cast iron and varied steel materials, along with a variety of coatings on the ring face, like gas-nitriding, adding wear resistance to the face of a ring.
Engineers at MAHLE have developed a 1mm top compression ring , 1mm second compression ring , and a 2mm oil control ring assembly pack that minimizes friction and maximizes sealing between the rings and your engine’s cylinder walls.
“Few would argue against the ability of thinner rings to free up horsepower in the right application,” states Maylish. “The typical concern from the racing world is usually first if they will last, and second, are they worth it? So, we asked our engineering team these questions to be able to convey answers to the racers.”
The modern ring pack is much more than just “thin.” In a departure from the typical materials, MAHLE’s metallurgical engineering advancements for these thinner ring packs rely on high-strength steel alloys. MAHLE’s new steel creates a ring far more durable than any cast-iron or ductile-iron option, which achieves proper sealing, thinner size, and less wear in motorsports applications.
The E9254 chrome-silicon steel used in the 1mm top ring successfully minimizes friction and is 35-percent stronger than any cast- or ductile-iron option. With this improved steel comes the ability to produce thinner rings that match the strength of thicker iron rings. The chrome silicon steel contains metallurgical advantages. The materials allow it to achieve ultra-flat ring flanks and a precision finish without machining damage. These two materials also maximize cuff resistance and ring-to-piston sealing.
Less tension by these rings throughout all four strokes of the engine results in less wear on the face of the rings, less drag on the rotating assembly, and less wear on the cylinder walls. – Joe Maylish, Mahle Motorsport
Reduced reciprocating mass is another strong point of the ring. With less mass, the piston and ring can travel up and down faster with higher RPM because of the lessened inertia points at the top and bottom dead center. According to Maylish, at these inertial points, this weight reduction can reduce or eliminate what is called “ring flutter,” which can decrease the ring-to-piston groove seal.
“Granted, you can apply these better materials to any size rings, but that will not overcome the differences in the cross-sectional area with the thinner rings,” Maylish says. “Those smaller dimensions make the rings lighter and more conformable.”
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Maylish adds, “This means you can design rings with less radial tension to achieve the same or better combustion gas sealing than a thicker ring. Furthermore, less tension throughout all four strokes of the engine results in less wear on the face of the rings, and less wear on the cylinder walls.”
Steel is also a better conductor of heat and can withstand a longer duration of high-temperature operation without concern for the rings losing tension.
The top ring in the 1.0, 1.0, and 2.0mm pack includes MAHLE’s patented HV385 thermal spray process. This coating is applied to the face of the top ring to improve bond strength of the 9254 steel underneath, as well as durability, and scuff resistance.
“This sprayed material actually becomes embedded into the top ring,” Maylish discloses. “The material is applied through a supersonic, thermal spray process with a liquid-oxygen-powered gun. The HV385 material impregnates itself into the ring face.”
The fundamentals of all ring designs call for the ring to be formed into a larger diameter than the mating cylinder bore. When installed, the compressed ring tries to expand to its natural diameter and pushes against the cylinder wall; that is called “tension.”
“The conformity of the steel material means you can design rings with less radial tension to achieve the same or better combustion gas sealing than a thicker ring,” Maylish explains. “Older ring designs rely on a comparative ‘brute’ tension force for piston sealing.”
The second 1.0mm ring is a reverse-twist taper-faced steel, and the oil rings are standard-tension oil control rings, all with a specific tension designed into them.
The engine bore is not perfectly round for any engine under power. The stresses on the bore — mechanical loading, deformation, and high temperatures — distort the bores. This distortion is typically measured in microns. It sounds minute, but those stressed bore shapes allow cylinder pressure to escape the combustion area past the rings.
MAHLE pioneered computer simulation software and other development tools that successfully minimized friction without sacrificing sealing capabilities. Maylish states, “These rings’ ability to conform to the cylinder walls increased measurable horsepower gains on the dynamometer during our development process. Furthermore, less tension throughout all four strokes of the engine results in less wear on the face of the rings and less wear on the cylinder walls.”
These thinner ring sets also allow the MAHLE engineers to develop new piston designs with shorter ring packs that eliminate the wrist pin bore from intersecting the oil ring groove. This clearance is a big plus for many small-block and LS engines. Now, the pin bore has space to sit below the oil ring groove, eliminating the need for support rails, which improves overall piston strength.
New technology for racing is on a constant quest for stronger, lighter, and better-performing designs. There is no question that these thinner MAHLE rings are an effective addition to the motorsports world, since they meet those criteria.
Not just a fad diet, the results from MAHLE’s dyno research and scores of other independent tests by performance engine builders cite the multiple benefits of piston and ring assemblies to not just be smaller, but to add a critical conformity between the rings and the cylinder wall. This “diet” provides a better seal to prevent compression gases from escaping around the piston, the biggest single job rings have.
Rings are rings right? Wrong! In addition to thickness and diameter, there are several different ring materials, styles, and coatings available to maximize performance in a variety of engine environments.
Not all that long ago, piston rings were all the same. They were heavy, thick, and you could have any material you wanted – as long as it was cast iron. Today, the performance engine builder has a broad span of material choices when it comes to piston ring materials and finishes. This is a direct result of the push for stronger ring materials faced with surviving the harsh environment of higher cylinder temperatures and pressures.
JE offers a variety of piston ring materials, styles, and coatings all built around different performance applications. If an off-the-shelf ring won’t cut it, custom ring services are also available such as grinding, lapping, and dyke cutting.Before we delve into materials, the responsibilities of a piston ring must be reviewed. While sealing combustion pressure is the obvious goal, an equally important function is to transfer heat from the piston to the cylinder wall. As rings become thinner, this heat transfer function becomes even more critical. Third, the rings must minimize the amount of oil that enters the combustion space. While many enthusiasts think that the second ring’s main task is a backup to sealing cylinder pressure, the reality is that 80 percent of its intended function is oil control to sweep up the remaining oil from the cylinder wall not removed by the oil ring.
For a performance engine, the piston buyer is faced not only with choosing the proper piston configuration and compression ratio, but also with selecting an optimized ring package. Much of this selection process is dictated by how the engine will be used. This must begin with the selection of the proper ring material. Ring widths and design can be chosen once the material has been finalized.
The current JE piston catalog lists a multitude of ring materials which may appear at first to be a daunting challenge. The first is carbon steel, which is a much more malleable material than cast iron, is able to handle higher temperatures without losing temper, and is better able to withstand bouts with detonation. Cast iron, by nature is very brittle and therefore not as strong as gas-hardened forged steel. Gas nitride top rings perform so well in so many different applications that even the OE now spends the extra money for this ring material for production engines.
While this sounds like a generic use material, carbon steel is also a great selection for high cylinder pressure applications like nitrous, turbo, supercharged, and high-rpm engines.
Steel nitrided top rings are an excellent ring in terms of durabilty and strength. They are formed from forged steel for strength and ductility, and the nitriding process makes them extremely hard and detonation resistant.Chrome faced rings were a popular option a few years back, but now have also succumbed to progress and are rarely employed in modern performance engines. The problem with many chrome facings was that they were extremely hard and difficult to break in properly and often suffered from flaking or cracking when exposed to detonation. Most dirt circle track applications have now converted to steel nitride ring packages. Some steel nitride rings are offered with a plasma molybdenum coating in addition to gas nitride.
Steel nitride top rings are a great choice for street performance applications, but may not be necessary from a cost standpoint for every engine. JE offers other options for the cost-conscientious engine builder. Hardened ductile iron is a great choice for serious street engines that do not demand the high temperature tolerance compatibility of a race engine. Ductile iron is a step up from typical cast iron with magnesium added to the grey cast iron to improve ductility –making this material more apt to bend instead of break.
Grey iron rings were the staple for many years. While more than adequate for a second ring in street applications, their brittle nature makes them sub par for outright performance in a top-ring setting.Some engine builders prefer a slightly older technology that they’ve had success with in the past including carbon steel rings with a harder chrome face (listed in the catalog as JC and JXC Series rings). This process is compatible with all cylinder bore materials except Nikasil.
Ductile iron is roughly twice the tensile strength of grey iron and tends to bend instead of breaking when subjected to stress. This makes it a great top ring selection when price is a consideration. Most often, ductile iron rings are offered with a plasma molybdenum (moly) face coating to make them more compatible with iron cylinders.
JE’s Premium Race Series is a great example of a ductile iron top ring that uses the more modern plasma-moly inlay technology. The plasma moly application produces a somewhat porous yet extremely hard, wear-resistant surface that retains oil and improves lubrication while also reducing friction. The plasma is created by spraying an alloyed powder containing Chromium, Molybdenum, and Nickel along with other trace elements into a small channel in the ring’s face. Using extreme heat, this powdered metal turns into a molten spray that offers superior adhesion characteristics which reduce the potential for flaking. This added porosity also improves initial ring break-in, reducing the time it takes for the rings to optimize sealing.
Back in the days of musclecars, a 5/64th inch ring thickness was state of the art. With modern materials, coatings and profiling, thinner rings have become the new staple. Shown is a 1mm top ring next to a well-worn dime.The discussion up to now has focused on the top ring. The second ring is subjected to far less heat and pressure than its top-rung brother and therefore does not demand as expensive a material. As an example, the Plasma Moly ring package listed in the JE ring chart is an excellent ring package specifying a carbon steel nitride top ring with a ductile iron second. A less expensive version of that combination would be the Sportsman Series ring package that specs a plasma-sprayed ductile iron top ring combined with a grey iron second ring.
Oil ring packages tend to be less cumbersome in terms of materials with most options offering carbon steel for the two sealing rings. The expander design may change but the most important question for oil rings is establishing overall tension based on how the engine will be deployed.
Once you’ve made your ring material selections, you can move on to the next level of decision making in terms of top and second ring design, face styles, radial thickness and perhaps any special treatments such as lapping and/or ultra or critical finish steps. This entire process is all aimed at optimizing ring seal and capturing all the cylinder pressure within the combustion space where it can do the most good.
The quest for more engine efficiency has auto manufacturers adopting thinner rings for greater efficiency when it comes to the family sedan. MAHLE has also embraced this technology, and much more in its motorsports division.
MAHLE Motorsports adopted a new thinner ring technology for performance and racing applications a few years back. The next stage for MAHLE is to educate racers about how these unique rings function and spell out the benefits for their next engine project.
We asked Joe Maylish, program manager for the MAHLE North American motorsports division, if material advancements sparked the new narrow rings compared to the thicker rings that have been the norm in the high-performance world for many years. His response is, “Yes, and more.”
“Material is one of the factors,” says Maylish. “MAHLE produces a huge volume of piston rings per year for automotive manufacturers and other applications. The volume of specialized raw materials we use with rings on the OEM side allows us to also engineer and manufacture effective rings for motorsports with an extension of that cutting-edge technology.”
Typically, piston rings can be constructed with different raw materials such as alloys of cast iron and varied steel materials, along with a variety of coatings on the ring face, like gas-nitriding, adding wear resistance to the face of a ring.
Engineers at MAHLE have developed a 1mm top compression ring , 1mm second compression ring , and a 2mm oil control ring assembly pack that minimizes friction and maximizes sealing between the rings and your engine’s cylinder walls.
“Few would argue against the ability of thinner rings to free up horsepower in the right application,” states Maylish. “The typical concern from the racing world is usually first if they will last, and second, are they worth it? So, we asked our engineering team these questions to be able to convey answers to the racers.”
The modern ring pack is much more than just “thin.” In a departure from the typical materials, MAHLE’s metallurgical engineering advancements for these thinner ring packs rely on high-strength steel alloys. MAHLE’s new steel creates a ring far more durable than any cast-iron or ductile-iron option, which achieves proper sealing, thinner size, and less wear in motorsports applications.
The E9254 chrome-silicon steel used in the 1mm top ring successfully minimizes friction and is 35-percent stronger than any cast- or ductile-iron option. With this improved steel comes the ability to produce thinner rings that match the strength of thicker iron rings. The chrome silicon steel contains metallurgical advantages. The materials allow it to achieve ultra-flat ring flanks and a precision finish without machining damage. These two materials also maximize cuff resistance and ring-to-piston sealing.
Less tension by these rings throughout all four strokes of the engine results in less wear on the face of the rings, less drag on the rotating assembly, and less wear on the cylinder walls. – Joe Maylish, Mahle Motorsport
Reduced reciprocating mass is another strong point of the ring. With less mass, the piston and ring can travel up and down faster with higher RPM because of the lessened inertia points at the top and bottom dead center. According to Maylish, at these inertial points, this weight reduction can reduce or eliminate what is called “ring flutter,” which can decrease the ring-to-piston groove seal.
“Granted, you can apply these better materials to any size rings, but that will not overcome the differences in the cross-sectional area with the thinner rings,” Maylish says. “Those smaller dimensions make the rings lighter and more conformable.”
Maylish adds, “This means you can design rings with less radial tension to achieve the same or better combustion gas sealing than a thicker ring. Furthermore, less tension throughout all four strokes of the engine results in less wear on the face of the rings, and less wear on the cylinder walls.”
Steel is also a better conductor of heat and can withstand a longer duration of high-temperature operation without concern for the rings losing tension.
The top ring in the 1.0, 1.0, and 2.0mm pack includes MAHLE’s patented HV385 thermal spray process. This coating is applied to the face of the top ring to improve bond strength of the 9254 steel underneath, as well as durability, and scuff resistance.
“This sprayed material actually becomes embedded into the top ring,” Maylish discloses. “The material is applied through a supersonic, thermal spray process with a liquid-oxygen-powered gun. The HV385 material impregnates itself into the ring face.”
The fundamentals of all ring designs call for the ring to be formed into a larger diameter than the mating cylinder bore. When installed, the compressed ring tries to expand to its natural diameter and pushes against the cylinder wall; that is called “tension.”
“The conformity of the steel material means you can design rings with less radial tension to achieve the same or better combustion gas sealing than a thicker ring,” Maylish explains. “Older ring designs rely on a comparative ‘brute’ tension force for piston sealing.”
The second 1.0mm ring is a reverse-twist taper-faced steel, and the oil rings are standard-tension oil control rings, all with a specific tension designed into them.
The engine bore is not perfectly round for any engine under power. The stresses on the bore — mechanical loading, deformation, and high temperatures — distort the bores. This distortion is typically measured in microns. It sounds minute, but those stressed bore shapes allow cylinder pressure to escape the combustion area past the rings.
MAHLE pioneered computer simulation software and other development tools that successfully minimized friction without sacrificing sealing capabilities. Maylish states, “These rings’ ability to conform to the cylinder walls increased measurable horsepower gains on the dynamometer during our development process. Furthermore, less tension throughout all four strokes of the engine results in less wear on the face of the rings and less wear on the cylinder walls.”
These thinner ring sets also allow the MAHLE engineers to develop new piston designs with shorter ring packs that eliminate the wrist pin bore from intersecting the oil ring groove. This clearance is a big plus for many small-block and LS engines. Now, the pin bore has space to sit below the oil ring groove, eliminating the need for support rails, which improves overall piston strength.
New technology for racing is on a constant quest for stronger, lighter, and better-performing designs. There is no question that these thinner MAHLE rings are an effective addition to the motorsports world, since they meet those criteria.
Not just a fad diet, the results from MAHLE’s dyno research and scores of other independent tests by performance engine builders cite the multiple benefits of piston and ring assemblies to not just be smaller, but to add a critical conformity between the rings and the cylinder wall. This “diet” provides a better seal to prevent compression gases from escaping around the piston, the biggest single job rings have.