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1250cc Conversion Kit for XL

1250cc Conversion Kit for 1986-2014 1200cc Harley-Davidson® Sportster® Models

FITMENT1250cc conversion kit

  • 1986-UP 1200cc Harley-Davidson® Sportster® models
  • 1986-UP 883cc Harley-Davidson® Sportster® models


  • Forged pistons – coated piston skirts with measurement window and S&S logo
  • Stock 1986 -2014 1200cc cylinders can be bored over to accept these pistons
  • Pistons have larger than stock valve pockets – accepts up to 2.00” valves


  • Silver powder coat finish
  • Wrinkle black (WBlack) powder coat finish


  • S&S 1250cc pistons w/rings and wristpins
  • S&S 3-9/16" bore cylinders
  • MSL head, base, and exhaust gaskets
  • Assembly lube
  • Instructions

S&S® 1250cc Cylinder and Piston Conversion Kits

Fitment Piston CR* Finish Part #
S&S Forged Flat top 10.3:1 Silver 910-0433
S&S Forged 5.5cc dome 10.3:1 WBlack 910-0443
S&S Forged Flat top 11.2:1 Silver 910-0436
S&S Forged 5.5cc dome 11.2:1 WBlack 910-0446
*Compression ratios given are with 60cc combustion chambers.

The Dynojet® 250i chassis dynamometer shows what a potent package the S&S® 1250cc kit for Harley-Davidson® Sportster® models can be. This chart compares a stock 2009 883cc engine before and after the 1250cc kit was installed. Over twice the horsepower! In addition to the 1250cc kit with 5.5cc pop-up dome forged pistons, the test bike was equipped S&S slip-on mufflers, stock EFI throttle body with an S&S tuned induction system, S&S 600 cams, and stock cylinder heads CNC ported by S&S.


Sportster cyclinder fin profile

S&S cylinders match the fin profile on 1986-’03 cylinder heads. Although there is a slight difference in the fin profiles of S&S cylinders and stock 2004 –’14 cylinder heads (shown left), the look is generally not considered to be objectionable. You decide!






  • Can not run stock 883 cylinder heads with this kit.
  • The cylinder fin profile does not perfectly match the fins on 2004 and later stock heads, but the difference is not considered to be objectionable. See Photos.
  • S&S does not recommend boring 2004 and later 883cc cylinders from 3" to 3-1/2" bore to increase engine displacement to 1200cc due to changes in factory cylinder and liner.  A smaller O.D. liner and large chamfer on the bottom of the spigot make boring the 883 cylinder not possible. New cylinders are recommended.