S&S 1250cc Big Bore Kit for Harley Sporster – Double the Horespower

S&S 1250cc Big Bore Kit for Harley-Davidson Sportster (1986-2014)

Harley-Davidson Sportster (883, 1200) Big Bore Kit

S&S Cycle has released a 1250cc Big Bore kit for 1986-2014 Harley-Davidson Sportsters, which can be bolted into the stock crankcases.

The kit includes 3-9/16” bore pistons, cylinders, and gaskets, and with other S&S components doubled the horespower of an 883cc engine.

Needless to say the new 1250cc conversion kit will appeal to the rider who wants to get the most from his or her bike, so S&S also recommends the S&S 600 cams and S&S CNC ported heads  to complete the package. Make the most of that displacement.

Choose from silver or wrinkle black powder coat finish that matches the stock finish on late model engines. Also, these kits are available with flat topped or 5.5cc pop-up forged pistons for a choice of compression ratios. Flat topped pistons yield 10.3:1 with stock 1200cc heads or S&S CNC ported heads. The pop-up pistons deliver 11.2:1.

If you’re looking for the largest bolt-on Big Bore kit available for the Harley-Davidson Sportster, this is it. The S&S 1250cc kit delivers great performance at an affordable price.

S&S 1250cc Big Bore Kit installed on an 883cc Sportster - Dyno Chart
S&S 1250cc Big Bore Kit installed on an 883cc Sportster – Dyno Chart

Dyno Chart with S&S 1250cc Big Bore Kit on 883cc Sportster

The Dynojet 250i chassis dynamometer shows the potency of the S&S 1250cc kit installed on a Sportster. The chart to the left (click to expand) compares a stock 2009 883cc engine before and after the 1250cc kit was installed. The 883cc engine produced 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.

Note – Not recommended for engines with stock 883 heads, but works great with stock 1200 heads and 883 or 1200 heads CNC ported by S&S.

S&S® 1250cc Big Bore Kits
for 1986-2014 Harley-Davidson® Sportster® Models
Finish Piston CR* Part # MSRP
Wrinkle Black Powder Coat Flat Topped 10.3:1 910-0443 $989.95
Wrinkle Black Powder Coat 5.5cc Pop-up 11.2:1 910-0446 $999.95
Powder Coat
Flat Topped 10.3:1 910-0433 $989.95
Powder Coat
5.5cc Pop-up 11.2:1 910-0436 $999.95
*Compression ratio based on stock or S&S CNC ported heads with 60cc combustion chamber

For additional information, visit S&S Cycle.


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