Harley-Davidson CVO Street Glide ST Big Bore Kits

This Screamin’ Eagle Stage III kit increases the relevant Milwaukee-Eight 117 engine to 122 cubic inches. Harley-Davidson describes a performance system developed and tested together, claiming up to 31% more horsepower and 18% more torque than the Original Equipment engine configuration. Those are manufacturer comparison figures for the specified setup, not a guaranteed gain for every motorcycle. The exact kit shown is part 92500139.

The film lays out the 4.155-inch big-bore bolt-on cylinders, forged 10.9:1 high-compression pistons and rings, SE8-511 camshaft and high-capacity tappets. A Stage III timer-cover medallion identifies the conversion. It also shows the multi-layer coated head gaskets, cylinder-base and cam-cover gaskets, and most of the necessary seals and gaskets supplied with the kit.

Confirm the exact Touring model and year before choosing the kit. The film requires ECM calibration using a separately purchased Screamin’ Eagle Pro Street Tuner. Its spoken description calls the system street-compliant, but the current product catalogue also marks it race-only with 49-state U.S. EPA compliance pending. The on-screen notice says sale and road-use legality vary by country. Check the current application, calibration and local status with a dealer; the film establishes no general UK or EU road approval.

This Screamin’ Eagle Stage III kit increases the specified 121-cubic-inch engine to 125 cubic inches. Part 92500141 is the Black Granite Highlighted version shown in the film. Harley-Davidson describes it as a system designed and tested by its performance team, combining greater displacement and compression with an SE8-511 camshaft. The intended benefit is stronger response when opening the throttle: the manufacturer says the extra torque and power may bring back some of the sensation of riding solo when carrying a passenger and luggage.

The kit includes 4.155-inch Big Bore bolt-on cylinders, forged pistons and rings with a stated 10.9:1 compression ratio, the SE8-511 camshaft and high-capacity tappets. The film also lays out the sealing parts: multi-layer coated head gaskets, cylinder-base and cam-cover gaskets, and most of the other necessary gaskets and seals. That is a defined package of engine components, not a promise that every additional fitting or calibration requirement is included.

Harley-Davidson claims up to 15% more horsepower and 17% more torque than the original-equipment CVO engine configuration. Against a CVO ST engine configuration, the stated increases are 5% in power and 4% in torque. These comparisons have different baselines; they should not be combined or applied to an unrelated engine specification.

The kit does not retain the original-equipment variable valve timing function. That is a substantive change to consider alongside the performance figures. The Black Granite Highlighted finish and the included Stage III timer-cover medallion complete the appearance shown in the close-ups.

The film’s street-compliance statement is specifically 49-state U.S. EPA compliance; it does not establish approval for UK or European road use. Use the exact 92500141 product action to check the selected motorcycle and its installation requirements before ordering. This explanation concerns the 121-to-125 kit, not another Stage III displacement or a complete engine.