50% OFF! Hot items selling fast—Grab them before they're gone!
S&S has been building big bore kits since the 60s and has it down to an absolute science. Our latest efforts are aimed at the Milwaukee Eight platform (2017 and newer big twins) and open up a whole new level of performance for these engines. Combining a new design forged piston with their 4.25 cylinders to net a tire melting 131 cubic inches when paired with their 4.625 stroker crank. We build our big bore kits and cranks to much tighter tolerances and with higher quality materials than the factory parts. This new piston/cylinder kit will be a solid platform for massive power.
Features & Benefits
131″ cam cover badge included.
Not for CVO 121″ models.
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| 2025 | Harley-Davidson | Softail Heritage Classic FLHC | – | – |
| 2025 | Harley-Davidson | FLHXU Street Glide Ultra | – | – |
| 2025 | Harley-Davidson | Road Glide Custom FLTRX | – | – |
| 2025 | Harley-Davidson | Softail Fat Boy FLFB | – | – |
| 2025 | Harley-Davidson | Softail Low Rider ST FXLRST | – | – |
| 2025 | Harley-Davidson | Street Glide EFI FLHX | – | – |
| 2025 | Harley-Davidson | Softail Breakout FXBR | – | – |
| 2024-2025 | Harley-Davidson | Road Glide Police FLTRXP | – | – |
| 2024 | Harley-Davidson | FLI Hydra-Glide Revival | – | – |
| 2023-2025 | Harley-Davidson | FXBR Breakout 117 | – | – |
| 2023 | Harley-Davidson | FLHFB Electra Glide Highway King | – | – |
| 2022-2025 | Harley-Davidson | FXLRS Low Rider S 117 | – | – |
| 2022-2025 | Harley-Davidson | FXLRST Low Rider ST 117 | – | – |
| 2022-2023 | Harley-Davidson | FLHXST Street Glide ST | – | – |
| 2022-2023 | Harley-Davidson | FLTRKSE CVO Road Glide Limited | – | – |
| 2022-2023 | Harley-Davidson | FLTRXST Road Glide ST | – | – |
| 2022,2025 | Harley-Davidson | Softail Street Bob FXBB | – | – |
| 2022 | Harley-Davidson | FXRST Low Rider El Diablo 117 | – | – |
| 2021-2024 | Harley-Davidson | FXBBS Street Bob 114 | – | – |
| 2021 | Harley-Davidson | FLH Electra Glide Revival | – | – |
| 2020-2024 | Harley-Davidson | FLTRK Road Glide Limited | – | – |
| 2020-2024 | Harley-Davidson | FXST Softail Standard 107 | – | – |
| 2020-2021 | Harley-Davidson | FXLRS Low Rider S 114 | – | – |
| 2019-2022 | Harley-Davidson | FLHT Electra Glide Standard | – | – |
| 2019-2020 | Harley-Davidson | FXDRS FXDR 114 | – | – |
| 2018-2024 | Harley-Davidson | FLHCS Heritage Classic 114 | – | – |
| 2018-2024 | Harley-Davidson | FLFBS Fat Boy 114 | – | – |
| 2018-2023 | Harley-Davidson | FXFBS Fat Bob 114 | – | – |
| 2018-2021 | Harley-Davidson | FLHC Heritage Classic 107 | – | – |
| 2018-2021 | Harley-Davidson | FLSB Sport Glide 107 | – | – |
| 2018-2021 | Harley-Davidson | FLSL Softail Slim 107 | – | – |
| 2018-2020 | Harley-Davidson | FXBB Street Bob 107 | – | – |
| 2018-2020 | Harley-Davidson | FXBRS Breakout 114 | – | – |
| 2018-2020 | Harley-Davidson | FXLR Low Rider 107 | – | – |
| 2018-2020 | Harley-Davidson | FLDE Deluxe 107 | – | – |
| 2018-2019 | Harley-Davidson | FXBR Breakout 107 | – | – |
| 2018-2019 | Harley-Davidson | FXFB Fat Bob 107 | – | – |
| 2018-2019 | Harley-Davidson | FLFB Fat Boy 107 | – | – |
| 2017-2025 | Harley-Davidson | FLHRXS Road King Special | – | – |
| 2017-2025 | Harley-Davidson | FLTRX Road Glide | – | – |
| 2017-2025 | Harley-Davidson | FLHX Street Glide | – | – |
| 2017-2025 | Harley-Davidson | Road King Police FLHP | – | – |
| 2017-2025 | Harley-Davidson | Electra Glide Police FLHTPI | – | – |
| 2017-2024 | Harley-Davidson | FLHTK Ultra Limited | – | – |
| 2017-2023 | Harley-Davidson | FLTRXS Road Glide Special | – | – |
| 2017-2023 | Harley-Davidson | FLHXS Street Glide Special | – | – |
| 2017-2023 | Harley-Davidson | FLHXSE CVO Street Glide | – | – |
| 2017-2022 | Harley-Davidson | FLHR Road King | – | – |
| 2017-2021 | Harley-Davidson | FLHTKSE CVO Limited | – | – |
| 2017-2019 | Harley-Davidson | FLHTKL Ultra Limited Low | – | – |
| 2017-2019 | Harley-Davidson | FLHTCU Electra Glide Ultra Classic | – | – |
| 2017-2019 | Harley-Davidson | FLTRU Road Glide Ultra | – | – |
| Product Name | Cylinder Kit |
| Style | Bolt-On |
| Model | Stroker |
| Color/Finish | Wrinkle Black / Highlighted Fins |
| Bore Size | 4.25″ |
| Displacement | 131″ |
| Stroke Length | 4.625″ |
| Compression Ratio | 11.0:1 |
| Units | Kit |
| Riding Style | Street |