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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallHarley-Davidson’s 2025 CVO Road Glide ST uses a 121-cubic-inch Milwaukee-Eight 121 High Output engine, rated by the company at 127 hp and 145 ft-lb. The 2025 CVO Road Glide and CVO Street Glide also have 121ci engines, but they use the VVT 121 variant, which Harley-Davidson rates at 115 hp and 139 ft-lb. The displacement is the same; the variant and the manufacturer’s claimed output are different.
What is the Milwaukee-Eight 121 High Output?
It is the engine Harley-Davidson specifies for the 2025 CVO Road Glide ST: a 121-cubic-inch V-twin with an 11.4:1 compression ratio. Harley-Davidson lists its output at 127 hp and 145 ft-lb of torque in the U.S. specifications for that model. Harley-Davidson’s 2025 CVO Road Glide ST page identifies the engine and its figures.
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Fanscreate Cam Cover, Transmission Side Cover for Harley Touring Softail M8,Clutch Outer Primary... | $159.00 | Buy on Amazon |
The company attributes the High Output package’s performance to a high-performance camshaft, a Heavy Breather intake and a rev limit raised to 5,900 rpm. Harley-Davidson calls it “the strongest factory-installed engine ever used in a production Harley-Davidson.” That is the manufacturer’s description, not an independent ranking or test result.
How does the VVT 121 compare?
The 2025 CVO Road Glide and CVO Street Glide use the Milwaukee-Eight VVT 121, not the High Output version. Harley-Davidson lists both at 121 cubic inches and an 11.4:1 compression ratio. Their U.S. specifications give the VVT engine 115 hp at 4,500 rpm and 139 ft-lb at 3,000 rpm.
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- ✅ 【 Cam Cover Fitment 】: Compatible with 2017‑2023 Harley‑Davidson models equipped with the Milwaukee‑Eight (M8) engine, including: Touring (Road King, Street Glide, Road Glide, Electra Glide, Ultra Limited) ; Softail family (Fat Boy, Heritage Classic, Breakout, etc.) ; Trikes (Freewheeler, Tri Glide) ; CVO Models ; ⚠️Note: Specifically designed for 107ci and 114ci M8 engine configurations.
- ✅ 【 Clutch Outer Primary Cover Fitment 】: Compatible with Harley-Davidson Milwaukee-Eight (M8) engines, including 107ci, 114ci, 117ci, and 121ci displacements ； Designed for 2017–2026 Touring models.
- ✅ 【Cable Transmission Side Cover Fitment】：This side cable transmission cover is compatible with: Touring: 2007-2013 & 2021-later M8 Touring/Trike models ； Dyna: 2006-2017 Dyna models (except FXDLS) ； Softail: 2007-2017 Softail models (except FLSS, FLSTFBS, FXCW, FXCWC, FXSB, FXSE) ； ⚠️Important Note: This cover is not compatible with models equipped with a hydraulic clutch system.
- ✅ 【 Hydraulic Clutch Transmission Side Cover Fitment 】: Compatible with 2014–2020 Touring models equipped with a Twin Cam engine and a pure hydraulic clutch system ； Compatible with 2017–2020 Touring models equipped with a Milwaukee-Eight (M8) engine and a pure hydraulic clutch system.
- ✅ Fanscreate Performance Premium CNC-machined Cam Cover ，Cable Transmission Side Cover ，Hydraulic Clutch Transmission Side Cover for Harley Davidson Touring Softail Milwaukee-Eight M8 Engines .Clutch Outer Primary Cover For Harley 2017–2026 Touring models.
| 2025 model | 121 variant | Displacement | Compression ratio | Harley-Davidson-listed output |
|---|---|---|---|---|
| CVO Road Glide ST | Milwaukee-Eight 121 High Output | 121 cu in | 11.4:1 | 127 hp; 145 ft-lb |
| CVO Road Glide | Milwaukee-Eight VVT 121 | 121 cu in | 11.4:1 | 115 hp at 4,500 rpm; 139 ft-lb at 3,000 rpm |
| CVO Street Glide | Milwaukee-Eight VVT 121 | 121 cu in | 11.4:1 | 115 hp; 139 ft-lb |
Sources: CVO Road Glide ST specifications, CVO Road Glide specifications and CVO Street Glide specifications. The CVO Road Glide ST page provides the torque figure but does not state an rpm for that figure; the table does not infer one.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the figures do—and don’t—tell you
The comparison establishes that Harley-Davidson offers two distinct 121ci engine variants in its 2025 CVO range and publishes higher peak-output figures for the High Output version. Displacement alone does not explain that difference, and the product specifications do not disclose a complete engineering comparison of the variants’ internal changes.
- These are Harley-Davidson’s stated specifications, not results from an independent, back-to-back dyno test.
- The figures do not establish which motorcycle is quicker in a particular real-world situation; no controlled acceleration comparison is provided.
- The available specifications do not support conclusions about comparative reliability, fuel economy or upgrade costs.
Which 121-equipped CVO should you compare?
Start with the motorcycle and engine variant: the CVO Road Glide ST is the High Output model, while the 2025 CVO Road Glide and CVO Street Glide use the VVT 121. If peak output is your comparison point, Harley-Davidson’s published numbers favor the High Output engine. Consider the figures as manufacturer ratings and consult the specification page for the exact model and market you are evaluating.
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