Performance

The Performance Roadmap: Understanding the Stages

Stage I: The "Breath of Life" (Bolt-Ons)

The foundation of any build. We improve airflow and sound to let your engine breathe.

• Upgrades: High-flow air cleaners, performance exhaust systems, and fuel management tuners.

• Result: Better sound, crisper throttle response, and a cooler-running engine.

Stage II: The Torque & Acceleration Pull

We add a performance camshaft to your Stage I setup to change the engine's personality.

• Upgrades: Performance Camshaft & Adjustable Pushrods.

• Result: Increased mid-range power—perfect for passing on the highway and quicker acceleration.

Stage III: The Big-Bore Transformation

We go inside the engine to increase displacement.

• Upgrades: Big-bore cylinders and high-compression pistons.

• Result: Massive increases in torque and horsepower across the entire RPM range.

Stage IV: Maximum Horsepower

The ultimate V-Twin experience, requiring precision engineering and expert tuning.

• Upgrades: Ported cylinder heads, larger throttle bodies, and high-flow injectors.

• Result: Track-ready power and peak top-end performance.

Performance Maintenance: Protecting Your Investment

High-performance builds require high-performance care. Every 5,000 miles, we perform a "Peak Potential" check:

• Mechanical Tuning: Precision adjustment of the primary chain, clutch, and final drive belt tension.

• Fluid Management: Synthetic engine oil, primary, and transmission fluid changes to handle increased heat.

• Control Lubrication: We lubricate and adjust throttle, brake, and clutch controls for smooth, safe operation.

• Electrical Stress Test: Checking battery health and cleaning connections to ensure your starter can handle high-compression builds.

Performance & Power Upgrades FAQ

1. What kind of power gains can I expect from a Stage Kit?

Performance gains scale with the depth of the build:

• Stage I: Expect a 5–10% increase in power just by letting the engine breathe.

• Stage IV: This is a total transformation, often yielding a 25% or greater increase in horsepower and torque through heavy engine work.

2. What is the highest-output engine currently available?

For riders demanding the peak of V-Twin engineering, the Screamin’ Eagle 135ci Stage IV Crate Engine is the street-compliant king. It is engineered to deliver a massive 130 hp and 143 lb-ft of torque.

3. How do the new Milwaukee-Eight (M8) engines compare?

The modern 2025–2026 lineup offers incredible factory performance that Big Swin’s can further optimize:

• M8 121 High Output (HO): Found in the CVO Road Glide ST, producing 127 hp and 145 lb-ft of torque with a 5,900 RPM redline.

• M8 121: Standard in CVO models, delivering 115 hp and 139 lb-ft of torque.

• M8 117: The powerhouse for new Street Bob and Heritage Classic models, providing roughly 104 hp and up to 126 lb-ft of torque.

4. Is performance only about the engine?

Absolutely not. To handle increased power, we also focus on Technical Upgrades that improve the "Better, Faster, Stronger" experience:

• Handling: Premium suspension kits (like Progressive 944 shocks).

• Stopping Power: High-performance Brembo braking systems.

• Airflow: CNC-ported cylinder heads and high-lift cams.

5. Can I upgrade my liquid-cooled Revolution Max engine?

Yes. For riders on the Nightster featuring the Revolution Max 975T (91 hp), we offer specialized tuning and component upgrades to maximize the potential of this modern liquid-cooled platform.