Key Questions to Ask When Ordering Piston Ring Material

Historically, piston ring sizes have been measured in fractional inches. Common measurements for top and second rings include 5/64-inch, 1/16-inch, or .043-inch, while oil rings are typically 3/16-inch. Modern engines have transitioned to metric measurements, with top and second rings ranging from 1.5mm to 1.0mm, and oil rings from 3.0mm to 2.0mm. These sizes have been the standard for years, but newer, thinner ring packages offer some significant advantages. Custom pistons can have rings as thin as .5mm (.020 inch). These thinner rings offer benefits such as increased horsepower and torque, while reducing weight and compression height. Substantial power gains can be achieved through the use of these modern, thinner rings and piston designs. Whether using thicker or thinner rings, proper piston ring installation pliers are essential. The only types of piston rings that can be 'spiraled' onto the piston are the oil ring's top and bottom rails. Avoid spirally installing compression rings on the piston.

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Think all piston rings are the same? Think again! Besides thickness and diameter, several ring materials, styles, and coatings are available to optimize performance in various engine conditions.

Not too long ago, piston rings used to be uniform and were predominantly made from cast iron—thick, heavy, and all the same. Nowadays, performance engine builders have a wide array of material choices for piston rings, thanks to advancements aimed at improving durability under higher cylinder temperatures and pressures.

Before selecting materials, it's essential to understand a piston ring's responsibilities. Besides sealing combustion pressure, a key role is to transfer heat from the piston to the cylinder wall. This heat transfer becomes even more critical as rings become thinner. Additionally, the rings must minimize oil entering the combustion space. Many believe the second ring's main job is to seal cylinder pressure; however, 80% of its role is oil control, sweeping up residual oil not removed by the oil ring.

For a high-performance engine, choosing the right piston configuration and compression ratio is crucial, as is selecting an optimized ring package. This choice largely depends on how the engine will be used and starts with selecting the appropriate ring material. After determining the material, you can finalize ring widths and design.

JE's piston catalog features various ring materials, which might seem overwhelming. The first type is carbon steel, a more ductile material than cast iron. Carbon steel can withstand higher temperatures without losing its temper, making it less prone to damage from detonation. Cast iron is brittle by nature, and lacks the strength of gas-hardened forged steel. Gas nitride top rings are highly versatile and cost-effective for production engines, delivering excellent performance across many applications.

While carbon steel might seem generic, it's ideal for high cylinder pressure engines, such as nitrous, turbo, supercharged, and high-rpm applications.

Chrome-faced rings were popular in the past but have become obsolete, rarely used in modern performance engines. They were tough to break in and often suffered from flaking or cracking under detonation. Most dirt track applications have switched to steel nitride ring packages. Some steel nitride rings come with an additional plasma molybdenum coating along with gas nitride.

For street performance applications, steel nitride top rings are excellent, though they might be cost-prohibitive for all engines. JE provides budget-friendly options for builders, such as hardened ductile iron, perfect for serious street engines that don't require the high-temperature tolerance of race engines. Ductile iron, enhanced with magnesium, is less brittle and more ductile than typical cast iron, making it less prone to breaking.

Some builders prefer traditional options like carbon steel rings with a hard chrome face, compatible with most cylinder bore materials except Nikasil. Ductile iron rings, offering twice the tensile strength of grey iron, bend rather than break under stress, making them an economical choice for top rings. Often, they come with a plasma molybdenum face coating to enhance compatibility with iron cylinders.

JE's Premium Race Series exemplifies modern technology, using ductile iron top rings with plasma-moly inlay. This creates a porous yet hard, wear-resistant surface that retains oil, improves lubrication, and reduces friction. By spraying alloyed powder containing Chromium, Molybdenum, and Nickel into a ring's face channel and applying extreme heat, a molten spray is produced, ensuring superior adhesion and reducing flaking risks. This porosity also aids in ring break-in, optimizing sealing more quickly.

While the focus has been on the top ring, the second ring doesn't face as much heat and pressure, thus requiring less expensive material. For instance, the JE plasma moly package includes a carbon steel nitride top ring and ductile iron second ring. A more affordable alternative is the Sportsman Series, featuring a plasma-sprayed ductile iron top ring and grey iron second ring.

Oil rings are simpler by comparison, typically using carbon steel for the two sealing rings. The expander design may vary, but the key question is determining the overall tension based on the engine's usage.

Once you finalize your ring material choices, you can proceed to the next decisions regarding top and second ring design, face styles, radial thickness, and any special treatments like lapping or critical finish steps. This entire process aims to optimize ring seal and capture all cylinder pressure within the combustion space for maximum efficiency.

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