Street Glide Special FLHXS (2021): Milwaukee-Eight 114 and Boom! Box GTS — "Every Element Optimized to Enhance the Rider's Interaction With the Bike"
White Lightning Harley's own confirmed dealer copy for this exact model year describes the genuinely upgraded interface built into the Special trim: "an evolved interface experience that offers a contemporary look, feel and function, with exceptional durability and features designed specifically for motorcycling. Every element is optimized to enhance the rider's interaction with the bike and connectivity with the world." That same copy confirms the blacked-out treatment that distinguishes this trim from the standard Street Glide: "blacked-out front forks, handlebars, tank console and exhaust for an aggressive, modern look."
Power comes from the Milwaukee-Eight 114, an air/oil-cooled V-twin displacing 114 cubic inches, a 4.016-inch bore and 4.5-inch stroke, and a 10.5:1 compression ratio, fed by Electronic Sequential Port Fuel Injection (ESPFI) through a 2-1-2 dual exhaust with tapered mufflers — a genuine displacement step up over the standard FLHX's Milwaukee-Eight 107.
White Lightning's own confirmed factory spec sheet lists a 26-degree rake with 6.8 inches of trail on a 64-inch wheelbase, a 26.1-inch laden seat height, and 4.9 inches of ground clearance, riding on black, glossy 19-inch front and 18-inch rear aluminum wheels — that same confirmed copy notes these are "designed to accentuate the long and low profile for an iconic, custom look." Suspension is described as "high-performing front and rear suspension with easily adjustable rear shocks," a real functional upgrade over the base model's simpler setup.
Confirmed fluid capacities list a 6-gallon fuel tank and 5.2 quarts of oil (with filter). Standard equipment includes ABS, Harley's Smart Security System, and cruise control — all confirmed standard rather than optional on this trim. JD Power's own confirmed 2021 pricing lists this exact model at $27,099 for Vivid Black (rising to $27,999 for the black-finish option), a genuine premium over the standard Street Glide's $22,699, reflecting the larger engine, infotainment upgrade, and blacked-out cosmetic package. This Milwaukee-Eight 114-powered configuration ran consistently across the Street Glide Special trim through subsequent model years before Harley's later engine and display updates arrived.
This factory service manual covers the procedures, torque specs, and diagrams needed to keep a 2021 Street Glide Special FLHXS running the way it was built to.
