Carrillo CPN-3681 CPN Piston Ring Set 3.681 in. Bore

The Carrillo CPN-3681 is a high-performance piston ring set engineered specifically for a 3.681-inch bore. Part of CP-Carrillo's acclaimed CPN ring series, these rings are designed to deliver maximum combustion seal with minimum parasitic drag — making them a top choice for performance and racing engine builds.

Ring Package Specifications:

• Top Ring: 1.2mm gas-nitrided carbon steel compression ring — compatible with both Nikasil and cast iron bores, offering superior durability and reduced friction versus thicker 1.5mm or 1/16" rings
• Second Ring: 1.5mm Napier-style (taper underhook groove face) cast iron ring — improves oil control over conventional taper-faced rings and allows the use of a lower-tension oil ring
• Oil Ring: 3.0mm three-piece assembly featuring gas-nitrided rails, a low-tension expander, and a mini-flex vent design for efficient oil control with minimal friction

Key Features:

• Gas-nitrided top ring compatible with Nikasil and cast iron cylinder bores
• Low-tension ring package reduces friction and increases efficiency
• Napier second ring profile enhances oil scraping and sealing performance
• Designed exclusively for use with CP-Carrillo pistons — OEM rings will not fit CP-machined ring grooves
• Cylinder prep requires plateau honing with a 35–40 degree crosshatch angle for optimal ring seal

The CPN-3681 ring set is sold as a single-cylinder set and is intended for use with the matching CP-Carrillo piston. Always verify ring end gap before installation and consult CP-Carrillo's ring installation guidelines for proper bore preparation and gap specifications.