Harley-Davidson ULTRA CLASSIC LOW Big Bore Kits

Genuine Harley-Davidson

3-7/8" Standard Bore. When combined with stock cylinder heads, these forged 3-7/8" pistons boost the compression ratio of your 3-7/8" big bore cylinder set-up. The combination results in a compression ratio of 10.5:1. Piston skirts feature a unique black coating for improved wear-resistance, better fit and reduced noise. These pistons include Titanium SST rings to withstand the stresses seen in racing. Complete kit includes pistons, rings, wrist pins and clips.

Genuine Harley-Davidson

When it comes to increasing engine power, there is no substitute for more cubic inches. With efficient filling of the air/fuel mixture, the bigger the displacement, the more power your engine can produce. In the past, the only way to increase the bore of your 96 or 103 cubic inch Twin Cam V-Twin motor was to tear down the motor and re-bore the engine cases to fit larger bore cylinder spigots. It was a labor-intensive and expensive process. Now, you can take your 96 or 103 cubic inch motor to a full 110 cubic inches without removing the engine from the chassis. The Screamin' Eagle team has engineered a 4" Big Bore Cylinder and Piston package that increase the internal bore from 3-7/8" to 4", without increasing the outside diameter of the cylinder spigot. The cylinder slips into the existing case bore without modification. This kit will add a whopping 7 cubic inches of displacement for more torque throughout the RPM range. The kit includes front and rear cylinders, system-matched pistons with rings and breathers.

Genuine Harley-Davidson

This multi-layered head gasket provides improved sealing for 3-7/8" Big Bore high performance engines. Sold in pairs.

Genuine Harley-Davidson

The most advanced Twin Cam performance cylinder head design available. Screamin' Eagle CNC Ported Maximum Velocity Area (MVA) cylinder heads create power across the entire RPM range by maximizing velocity through the intake ports. Increased air speed velocity through the ports is achieved by "right sizing" port volume at 98cc, lowering the port roof, and by precision-machining the shape of the port to complement the giant 2.120" intake valves. Screamin' Eagle CNC-Ported MVA Cylinder Heads conquer a unique engineering challenge, and provide the highest possible torque and acceleration at any RPM. MVA Heads will boost the punch of a 103" engine. When paired with high lift cams, MVA Heads can give a 110" or 113" motor everything it needs to achieve new levels of performance. Countless hours of dyno testing resulted in a 95cc combustion chamber that performs in perfect balance with the port size and shape, and reduced detonation. MVA Heads feature Screamin' Eagle Race Springs that permit the use of high lift cams (up to.660"), and are machined to accept automatic compression releases (sold separately) for easier starting. MVA Heads are manufactured and assembled at Harley-Davidson's world class engine factory in Milwaukee, ensuring every set is made to exact tolerances.

Genuine Harley-Davidson

If you're looking to build a fast, track-ready 103, this kit eliminates the guess work. Kit includes CNC-Ported Factory Cylinder Heads with high performance valve springs, matching high-compression forged aluminum 10.5:1 pistons, SE-259E cams for higher lift for a given duration, Perfect-Fit Pushrods to accommodate the higher cam lift, and a 58mm throttle body with High Flow Injectors to feed the beast. Kits for Twin Cam 96 models include Big Bore cylinders, and the Twin Cam 103 kit uses the Original Equipment 103 cylinders. The kit also includes high-performance clutch spring and sprocket retention hardware to put the power to the ground. Kit includes top end gaskets.

Genuine Harley-Davidson

Build a fast, reliable 110 cubic inch Twin Cam hauler without having to remove the motor from the chassis. This Stage III Street Performance Kit combines system-matched Screamin' Eagle big bore cylinders, high compression pistons and performance cams and valve train components with the Original Equipment cylinder heads for a cost-effective boost in torque and performance.

Genuine Harley-Davidson

4.060" Standard Bore. Forged from high-strength aluminum, these 10.5 to 1 ratio pistons feature nickel-plated surfaces for enhanced durability, and a special Teflon coating for improved wear-resistance required for racing applications. These pistons include Titanium SST rings to withstand the stresses seen in racing. Complete kit includes pistons, rings, wrist pins, and clips.