Recommended Additional Upgrades
03
Uma Laser Iridium Spark Plug
Improve ignition with Uma Racing Laser Iridium Spark Plug.
The UMA Racing 63mm Ceramic Cylinder Block Kit is a high-end “Big Bore” upgrade for the Yamaha 155cc VVA engine platform (R15 M, R15 V3/V4, MT-15, XSR 155, Aerox, and NMAX). By increasing the bore from the stock 58mm to 63mm, your displacement jumps to approximately 183cc.
This kit is widely considered the gold standard for high-performance street builds because it combines a low-friction ceramic coating with a heavy-duty forged piston.
Key Features
-
Ceramic Coating: The cylinder bore is treated with a ceramic composite that is significantly harder than standard steel. This provides superior heat dissipation and reduces friction, allowing the engine to rev more freely and run cooler under load.
-
Forged Piston: Unlike stock cast pistons, the Forged Piston is manufactured under extreme pressure, making it much stronger and lighter. It can handle the increased combustion temperatures and higher RPMs of a modified engine without cracking.
-
Enhanced Water Jacket: UMA has redesigned the cooling channels (water jacket) around the cylinder. It holds a larger volume of coolant than the stock block, which is essential for maintaining a stable temperature at 183cc.
-
Stability & Reliability: The ceramic material expands and contracts less than iron, meaning the “piston-to-wall” clearance remains consistent even during aggressive track sessions or long highway tours.
Technical Specifications
| Feature | UMA 63mm Kit Details |
| Bore Size | 63mm (Approx. 183cc) |
| Piston Type | Forged Aluminum (Lightweight/High-Strength) |
| Compression Ratio | Approx. 12.2:1 (High Compression) |
| Cylinder Type | Ceramic Coated (Liner-less technology) |
| Compatibility | R15 V3/V4/M, MT-15, XSR 155, WR155R, Aerox/NMAX V2 |
| Included in Kit | Cylinder Block, Forged Piston, Rings, Pin, Circlips, & Gaskets |
Performance Advantage
-
Massive Torque: The increase in displacement provides a huge boost in “grunt” (torque), making the bike much faster at pulling out of corners and overtaking.
-
Increased Horsepower: When paired with a racing exhaust and ECU, this kit can push an R15 from its stock ~18hp to 22-25hp+ depending on the tune.
-
VVA Optimization: The extra displacement makes the transition to the VVA (Variable Valve Actuation) much more powerful, effectively giving you a “second wind” at high RPMs.
Important Requirements
You cannot simply “bolt this on” and ride. To ensure the engine doesn’t blow up, you must have:
-
Programmable ECU: You need a racing ECU (like UMA M5 or M9) to increase the fuel delivery. The stock ECU will run the 183cc engine too lean, which will melt the piston.
-
High-Flow Injector: A larger injector (typically 160cc/min to 180cc/min) is usually required to match the increased air volume.
-
Upgraded Cooling: While the block has a better water jacket, using a high-performance coolant or a larger radiator is recommended for long-term health.
| Product Specifications | What’s in the Box? |
|---|---|
|
|
FAQs
Do I need ECU tuning?
Yes, highly recommended after installing any big bore kit.
Is forged piston better?
Yes, forged pistons are stronger and better for high-performance use.
Can I use this daily?
Yes, with proper tuning and maintenance, though it is built for performance-focused riders.
