CJM x Diamond EJ25, Unlimited Series Piston & Ring Pack

CJM x Diamond Unlimited Subaru EJ257 Piston & Ring Set

Diamond Forged Pistons for Subaru Engines — CJM Spec

Proven in professional motorsport—including top-level drag racing and NHRA competition—Diamond pistons are trusted by leading engine builders for their unmatched strength and reliability under extreme conditions.

Diamond’s forged pistons are among the strongest options available for Subaru performance builds. Developed to CJM specifications, these pistons are engineered for high-performance racing engines producing 1150+ horsepower. Built to withstand the extreme cylinder pressures of high-boost, power-adder Subaru applications, they utilize Diamond’s advanced forging technology to deliver exceptional tensile strength and long-term durability.

Each piston incorporates premium, custom-level features—thermal-barrier crown coating, skirt coating, lateral gas ports, optimized pin oiling, and other performance-enhancing refinements. Diamond’s CJM-spec forged pistons are the ideal choice for Subaru builders seeking maximum reliability, efficiency, and power at extreme output levels.

CJM-Spec Motorsport-Derived Ring Pack

Developed using top-level motorsport technology from Formula 1, NASCAR, and NHRA, this ring pack was engineered to improve sealing efficiency and drastically reduce blow-by—especially in high-performance engines producing 950+ horsepower running Race Gas or Ethanol fuels.

Gapless Gas-Ported Top Ring
Strategically placed horizontal gas ports allow combustion pressure to load the ring from behind, dramatically improving ring seal and enhancing power potential.

Reduced Oil Contamination
Superior sealing minimizes blow-by, reducing the contamination of engine oil with combustion byproducts and maintaining more stable performance across long intervals.

PVD Face Coating
Both the top and second rings utilize a low-friction PVD coating that reduces wear, controls heat, increases sealing consistency, and significantly extends service life under extreme racing conditions.

Special Note — Not Suitable for Street Use
Due to the increased vacuum generated by the motorsport-style gapless ring configuration, some smoke at startup may occur. This ring pack is intended strictly for racing applications.

Key Features

·        CJM Specification: Designed in collaboration with CJM for maximum strength, performance, and durability.

·        High-Performance Racing Design: Engineered to support 1150+ HP Subaru engines and extreme boost levels.

·        Advanced Forging Technology: Diamond’s proprietary forging process maximizes tensile strength under severe loads.

·        Skirt Coating: Reduces friction, minimizes wear, and lowers cold-start noise.

·        Thermal-Barrier Crown Coating: Ceramic layer reflects heat into the chamber, reducing crown temperatures and improving combustion efficiency.

·        High-Strength Wrist Pins: Thick-wall Trend Performance pins built for high-power, power-adder applications.

·        Lateral Gas Ports: Ensure strong top-ring seal at high RPM and high boost.

·        Optimized Pin Oiling: Enhanced lubrication for reduced heat, friction, and long-term wear.