S&S CYCLE Piston Kit 106-3688

If you're running a Big Twin and want measurable power gains without a complete engine rebuild, this S&S piston kit delivers a straightforward path to 1250cc displacement. The 10.3:1 compression ratio strikes a practical balance between increased output and street-manners reliability. You'll see noticeable gains in mid-range torque and top-end power—the kind of improvement that transforms how your bike pulls through the gears.

This is a bolt-on upgrade for owners committed to extracting more from their existing platform. The flat-top design works with both stock and performance cylinder heads, though pairing these pistons with S&S CNC ported heads will maximize your investment. Installation is straightforward on most Big Twins, though boring your cylinders to the 3-9/16" specification requires professional machine work.

• Cast flat-top pistons
• 10.3:1 compression ratio
• 1250cc total displacement
• 3-9/16" bore diameter
• Fits 1984–'99 HD Big Twins
• Compatible stock 1200cc heads
• S&S ported heads recommended
• Works 1200cc cylinders (stock)
• Works 1986–'03 883cc cylinders
• Not compatible 2004–'16 883cc
• Requires cylinder boring
• MPN: 106-3688