M8 Series

NEW FOR 2026!

M8 SERIES EXHAUST SYSTEM w/  Indexable Cylinder Backpressure Technology.

The M8 Series Exhaust System is a purpose-engineered exhaust platform designed around high-output, big-inch Harley-Davidson® V-twin engines. Every design decision prioritizes exhaust gas velocity, cylinder balance, and high-horsepower stability—eliminating the compromises found in generic large-diameter systems.

Engineered for 124–143ci+ Milwaukee-Eight platforms, the M8 SERIES can be configured to support 240+ horsepower while maintaining precise control over exhaust pulse timing and scavenging characteristics.

Two Size-Specific Configurations

The M8 Series is offered in two primary tube diameters, allowing the exhaust to be properly matched to engine displacement, airflow demand, and operating RPM range:

131 Series:

Engineered for riders who demand strong, usable power, these step tuned headpipes are designed to maximize exhaust efficiency where it matters most. The progressive diameters increase in precisely calculated steps from 1.87" to 2.00" to 2.12" in order to maintain higher exhaust gas velocity, helping build hard-hitting midrange torque and crisp throttle response.

Optimized for engines 124-131 cubic inches, this design balances flow and velocity to deliver smooth power delivery without sacrificing low- and mid-RPM performance. Ideal for high-performance builds looking for stronger pull and improved rideability.

135+ Series

Built for extreme displacement and high-RPM performance, the 135+ Series is engineered to handle the massive exhaust volume demanded by today’s biggest V-twin builds. Featuring a progressive step-tuned design that expands from 1.87" → 2.00" → 2.12" → 2.25", this system maximizes flow while maintaining control over exhaust velocity where it counts.

Designed specifically for 135ci and larger engines, the added final step supports high airflow at elevated RPM, helping big-inch motors breathe freely and pull hard without restriction. The result is a system optimized for peak performance in aggressive, high-output applications.

Both 131 and 135+ systems share identical routing, collector placement, and chassis fitment, ensuring consistent installation and clearance. The only difference is the primary exhaust tube diameter, allowing airflow to be scaled correctly without altering exhaust geometry.

Advanced Exhaust Control

Each system can feature Indexable Cylinder Backpressure Technology, allowing each individual headpipe to be tuned independently before the merge collector. This enables precise balancing of cylinder-to-cylinder exhaust pressure, improving combustion efficiency, reducing reversion, and stabilizing air/fuel ratios under load—critical for large-displacement and high-compression builds.

Thermal Management

These exhaust systems are offered with optional full-length, one-piece heat shields, providing uniform thermal coverage while eliminating visual breaks. This design improves heat management, long-term durability, and delivers a clean, uninterrupted appearance.

Built for Extreme V-Twin Performance

The M8 Exhaust System is not simply oversized—it is engineered to scale with power. From displacement-specific primary sizing to indexable backpressure control, this system is designed for builders and riders pushing Harley-Davidson V-twin performance far beyond factory limits.