Name: 130CC (54MM) ALUMINIUM BIG BORE KIT | PERFORMANCE SERIES (ACTIVA110 | NAVI110)
Brand: YUMINASHI
SKU: 12101-KWP-540SP
Price: 3910.4 ZAR
Availability: InStock

Description

● YUMINASHI 130CC (54MM) BIG BORE KIT | PERFORMANCE SERIES (12101-KWP-540SP)

Part Number: 12101-KWP-540SP

● Unlock the true potential of your engine. Engineered for mechanics who prioritize reliability, heat management, and endurance. Bumping displacement on air-cooled engines like the Navi 110 or Activa 110 isn't just about hogging out a cylinder; it’s about controlling extreme thermal loads.

● This 130cc 54mm Performance Series kit removes the thermal restrictions of the stock cast iron block while delivering a highly durable bottom-end foundation.

1. The Aluminium Advantage: Aluminium vs. Cast Iron

The factory cast iron KWP cylinder is essentially a heavy heat sink that does a terrible job at cooling. It traps heat, drops air density, and causes severe power fade once the engine heat-soaks.

● Aluminium Block: Our 54mm aluminum cylinder slashes the block weight by more than half while vastly accelerating thermal exchange.
● The Physics of Power: This faster heat dissipation is critical to avoiding pre-ignition and keeping your engine responsive after miles of hard riding.

2. The Heart of the Kit: YPS-12 Proprietary Alloy & Optimized Piston Design

A big bore is only as good as the material it is cast from. Cheap aftermarket tuning pistons often use lower-grade generic AC2B cast blends to maximize profit margins, but these alloys soften rapidly and collapse under high Exhaust Gas Temperatures (EGTs).

For this kit, our YUMINASHI PERFORMANCE SERIES eutectic cast piston is cast from YPS-12, our proprietary low-expansion aluminum silicon alloy. Based on the premium JIS AC8A equivalent, eutectic cast specification, this 12% silicon material boasts an exceptionally low thermal expansion coefficient. This ensures that the piston maintains its precise shape and clearance even under intense engine heat. Because of this thermal stability, we are able to machine the piston to a precise 0.035mm to 0.045mm piston-to-cylinder wall clearance, effectively eliminating piston slap while maintaining absolute safety under extreme loads.

● Optimized Crown Geometry (The "Pancake" Dome): We designed the piston with a raised center plateau. This specific geometry serves two critical functions for thermal management and efficiency:
- Maximum Scavenging: By occupying more clearance volume at Top Dead Center (TDC) on the exhaust stroke, the dome physically forces out a much higher percentage of superheated, inert exhaust gases. Less trapped residual exhaust means a cooler, oxygen-rich intake charge on the next stroke.
- Squish Band Velocity: The flat outer perimeter of the piston creates a high-velocity "squish band." As the piston reaches TDC on compression, this band violently forces the air/fuel mixture toward the center spark plug. This accelerates the flame front for a faster, cleaner burn, which proactively suppresses the end-gas detonation (knock) that destroys tuned air-cooled engines.
● High-Temperature Hardness (1.08% Nickel): The >1% Nickel content maintains the alloy's structural rigidity at high heat (yielding 127 MPa at 300°C). This prevents the ring lands from softening and blowing out under high dynamic compression.
● Rapid Thermal Transfer (1.05% Copper): Exceptional thermal conductivity aggressively pulls heat away from the piston crown, transferring it to the cylinder wall to drastically reduce the risk of a melted dome.
● Ductility over Brittleness (12.08% Silicon): At roughly 12%, this is a true eutectic cast. Unlike rigid hyper-eutectic racing pistons that shatter instantly if the engine knocks, this alloy absorbs combustion shockwaves and minor detonation without cracking.

3. Friction & Sealing Upgrades

● Dry Film Lubricant Skirt Coating: The dark gray coating on the piston skirts is a specialized dry film lubricant. It provides critical cold start protection by preventing direct metal-to-metal contact between the aluminum piston skirt and the cylinder wall when oil pressure is low or absent during a fresh engine start. Additionally, the micro-structure of the coating holds microscopic amounts of engine oil. This lowers initial friction, prevents scuffing or galling during the critical engine break-in period, and helps maintain localized lubrication under extreme loads.
● 12mm DLC Coated Piston Pin: We replaced the standard steel pin with a Diamond-Like Carbon (DLC) coated pin. This ultra-low friction barrier prevents galling against the connecting rod under high RPMs and extreme temperatures.
● 0.58mm Copper Head Gasket: Copper provides exceptional lateral thermal conductivity out to the cooling fins, eliminating hot spots around the combustion chamber while ensuring a blowout-proof crush seal under increased dynamic compression.
● 1mm Thicker Cylinder Base Gasket: This thicker gasket acts as a thermal break. It actively insulates the crankcase from the conductive heat of the cylinder block, keeping your engine oil cooler and preventing thermal runaway in the bottom end.

4. Superior Ignition: NGK G-POWER PLATINUM SPARK PLUG Included

Increased displacement and the raised YPS-12 piston dome drastically alter cylinder pressures and clearances. The stock heat range #7 projected spark plug is no longer sufficient or safe.

This kit includes the heat range #8 NGK PLATINUM G-POWER CR8EGP to proactively suppress detonation. Here is why this specific plug is mandatory for this build:

● Non-Projected Tip: Moving away from a projected tip is a crucial safety upgrade for high-compression builds. It guarantees the raised piston dome will not make physical contact with the plug, while keeping the ground strap tucked closer to the cooling passages to lower the risk of engine knock.
● Platinum Precision (0.6mm): The fine-wire 0.6mm platinum center electrode ensures superior ignitability and a highly concentrated spark.
● 98% Pure Copper Core: Working in tandem with the aluminum cylinder and copper head gasket, the plug's 98% pure copper core aggressively pulls blistering heat out of the center electrode, preventing pre-ignition and keeping the engine responsive.
● Benefits: Expect faster acceleration, superior ignitability, and improved fuel efficiency compared to standard nickel plugs.

● BUILDING THE ULTIMATE NAVI | Recommended Setup:

● TO GET THE ABSOLUTE MOST OUT OF THIS 130CC CYLINDER, WE STRONGLY RECOMMEND PAIRING IT WITH THE FOLLOWING COMPONENTS TO ELIMINATE THE FACTORY BOTTLENECKS:

1. The Valvetrain (The SS240 Super Sport Camshaft)

● The 54mm bore creates the suction, but the cam dictates the flow. Our SS240 Camshaft is designed to extend the powerband. When paired with the 130cc kit, this cam allows the engine to breathe deeply at higher RPMs where the stock cam falls flat, transforming the character of the bike from a commuter to a sport machine.

2. Breathing & Fueling (Intake & Exhaust)

● Carburetor: The stock carb cannot feed a 130cc engine effectively. We recommend the YUMINASHI PE24FL PRO (Flange Type) (LINK) which comes stock with a #115 main jet and #38 slow jet installed.
● Manifold: The stock manifold should be modified to taper down from inner diameter 25.9mm at the carburetor side, to 24.5mm at the cylinder head side.
● Porting: As per our flow calculations, to fully utilize the YUMINASHI PE24FL PRO, the intake port should be opened up to match the 24.5mm manifold diameter to ensure laminar flow.
● Exhaust Header: Based on the 54mm displacement and exhaust valve area, the stock header pipe is too restrictive.
For this kit, we recommend upgrading to a custom header with a 22mm internal diameter 250mm long, stepping up to 25mm inner diameter for 200mm long, to end up to 28-30mm for 150mm-200mm, with a Muffler Canister Core of 30-32mm (200mm to 250mm long) to evacuate exhaust gases quickly and prevent heat buildup.

3. Transmission (Stage-3 Variator) The Honda Navi ECU has a frustratingly early RPM limiter. Even with more power, you will hit this wall.

The Solution: The Yuminashi Stage-3 Speed Control Variator Set.
How it works: This variator changes the gear ratio, allowing the bike to travel at higher speeds while keeping the engine RPMs lower. It utilizes the massive torque increase from the 130cc kit to pull a taller gear ratio, effectively bypassing the top-speed limitations of the stock ECU.

➲ To prevent flow separation and create a perfect velocity funnel, the entire intake tract must taper progressively from the 25.9mm carburetor exit down to the 22.1mm inner valve seat.

● Intake Manifold Modifications:

Carburetor Side: Widen the manifold at the carburetor side to exactly 25.9mm to create a seamless transition from the PE24FL PRO carburetor.
Engine Side: Taper the manifold exit at the cylinder head side down to 24.5mm.

● Cylinder Head Port Modifications:

Port Entrance (Manifold Face): Widen from the stock 22.5mm to 24.0mm to 24.5mm. Setting this exactly at 24.5mm will perfectly match the modified manifold and eliminate any stepped ledge that causes turbulence.
The Path: Blend the port linearly from the 24.5mm entrance down to the 22.1mm valve seat, ensuring you do not widen the middle section beyond this taper.

● YUMINASHI Tooling Allocation:

The YUMINASHI genuine single-groove Aluma-Cut burrs will cleanly sheer the aluminum without clogging, provided you use the right size for the corresponding geometry.

8mm Aluma-Cut Burr (LINK): Dedicate this to bulk material removal and straight-wall tapering. The larger 13mm cutting head provides a stable, wide cutting surface to efficiently open the manifold to 25.9mm and the port entrance to 24.5mm while keeping the walls flat and linear.
6mm Aluma-Cut Burr (LINK): Dedicate this to the critical zone inside the cylinder head. The smaller 10mm cutting head provides the exact visibility and clearance required to shape the short turn radius and blend the port roof into the bowl area without accidentally cutting into the 22.1mm inner valve seat or nicking the valve guide.

※ Stop cutting once the dimensions are reached and follow up only with a #60 grit Sanding Flap Wheel Ø25x25mm (Sanding Flap Wheel is included in the carburetor set) on all modified surfaces to maintain the necessary boundary layer turbulence for wet-flow fuel suspension.
※ 2 Pieces of #60 grit Sanding Flap Wheels Ø25x25mm are included in the carburetor set, to modify the manifold and the cylinder head. The 25mm diameter will shrink down while you are using these sanding flap wheels, so you can work based on the diameters as described above...

SMART SHOPPER TIP:
※ BUYING MORE THAN 1 PIECE CUT THE TRANSPORT PRICE, AND YOU RECEIVE A 10% DISCOUNT ON TOP OF IT!

※ B2B:

Purchases between 2 & 4 pieces of this product will receive a 10% DISCOUNT
Purchases between 5 & 9 pieces of this product will receive a 15% DISCOUNT
Purchases between 10 & 19 pieces of this product will receive a 20% DISCOUNT
Purchases between 20 & more pieces of this product will receive a 25% DISCOUNT
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