UMA RACING HIGH COMPRESSION COMPOSITE CYLINDER BLOCK 63MM FORGED PISTON YAMAHA R15 V3/V4

The UMA Racing Composite Cylinder Block (63mm) with Forged Piston is a premium, track-tested big-bore performance kit designed for small-displacement liquid-cooled engines (most notably popular on platforms like the Yamaha R15 V3/V4, MT-15, XSR155, WR155R, etc.

By increasing the cylinder bore from the stock 58mm to 63mm, this kit increases engine displacement from 155cc to approximately 177cc–180cc (depending on the stock stroke), delivering massive gains in both low-end torque and peak horsepower.

Key Components & Technologies

1. Ceramic Composite Cylinder Block

• Exceptional Heat Dissipation: The block features a high-density ceramic coating on the inner sleeve. Ceramic transfers heat significantly faster than traditional cast iron or steel liners, keeping engine temperatures low under high-load racing conditions.

• Low Friction Coefficient: The smooth ceramic surface reduces friction between the piston rings and the cylinder wall, freeing up “lost” horsepower and minimizing internal wear.

• Extreme Hardness: The composite liner is highly resistant to scoring and scratching, ensuring long-term compression stability even when subjected to high engine speeds.

2. Premium Forged Piston

• Superior Structural Strength: Unlike standard factory pistons which are cast (poured into a mold), UMA’s piston is forged from a solid block of high-grade aluminum alloy under immense pressure. This alters the grain structure of the metal, making it incredibly dense and tough.

• Lightweight Profile: Forging allows the piston walls to be thinner and lighter without sacrificing structural integrity. A lighter piston reduces reciprocating mass, allowing the engine to rev up faster and putting less strain on the connecting rod.

• High Compression Design: The crown of the piston is precision-machined to optimize the combustion chamber shape, increasing the compression ratio for a more volatile and powerful combustion stroke.

Technical Specifications

Why Upgrade to the UMA 63mm Forged Kit?

1. Massive Torque Gains: The increased displacement provides an immediate and dramatic boost in mid-range torque. This makes the bike pull aggressively out of corners and minimizes the need to constantly downshift on inclines or during overtakes.

2. Built for High Boost/RPM: If you plan to couple this kit with high-lift camshafts, a larger throttle body, or secondary performance modifications, the forged piston is a necessity to handle the increased combustion pressures safely.

3. Enhanced Reliability: The combination of a cooling-efficient ceramic sleeve and a robust forged piston means this kit often runs cooler and lasts longer than budget iron-sleeve big-bore kits.

Essential Supporting Modifications

Installing a 63mm big-bore kit radically changes the engine’s internal dynamics. To run this setup reliably and safely, the following supporting mods are highly recommended:

• Standalone Programmable ECU: The factory ECU cannot supply enough fuel for an extra 25cc. You must use a standalone ECU (like the UMA Racing M5 or PowerTronic V4.0) to precisely richen the fuel map and adjust ignition timing to prevent a lean burn, which can melt components.

• Upgraded Fuel Injector: A higher-flow injector (e.g., 160cc/min to 180cc/min) is usually required to match the increased air volume entering the larger cylinder.

• High-Flow Exhaust & Air Filter: To maximize the volumetric efficiency of the 177cc engine, a free-flowing exhaust system is necessary to clear out waste gases efficiently.