SP Concepts Big Bore Exhaust for 2018-2026 Harley Softail

Product Description

SP Concepts Big Bore 4.5 Exhaust for 2018-2026 Harley M8 Softail

Give your Milwaukee-Eight Softail the airflow, torque and aggressive sound of a true performance exhaust with the SP Concepts Big Bore 4.5. Designed for riders running everything from stock-displacement Milwaukee-Eight engines to serious big-bore builds, this system combines stepped stainless steel headers with a large 4.5" high-flow muffler engineered to support strong bottom-to-midrange power.

The heart of the Big Bore 4.5 is its oversized 4.5" rolled-cone muffler and stepped internal baffle, which transitions from 2-1/4" to 2-1/2". The increased muffler and baffle volume provides additional exhaust flow for larger-displacement engines while maintaining the exhaust velocity needed for responsive street performance. SP Concepts states that, when properly tuned, the system can accommodate Milwaukee-Eight engines ranging from 88" through 143".

The headers are constructed from heavy-duty .065" stainless steel and step from 1-3/4" to 1-7/8" and then to 2" at the collector. This stepped design helps maintain exhaust velocity through the RPM range while providing the flow capacity needed for high-output M8 combinations.

For riders looking for additional performance, optional Pro Flo Chambers are available. These chambers are designed to assist with exhaust reversion and expansion, helping produce additional torque and horsepower beyond the standard system while adding a distinctive custom appearance.

Every Big Bore 4.5 system is hand TIG welded from top to bottom and uses machined stainless steel header collars for durability and precise fitment. The system includes 18mm O2 sensor bungs with 12mm adapters, allowing use with factory oxygen sensors or compatible wideband and autotune sensors.

Choose from Stainless, Black, Polished, Black ONYX or Platinum finishes. The exhaust can also be ordered with or without Pro Flo Chambers and with the appropriate Low Rider ST configuration.

Fitment

Fits most 2018-2026 Harley-Davidson Milwaukee-Eight Softail models.

Compatible Models: Fits applicable Street Bob, Low Rider, Low Rider S, Low Rider ST, Sport Glide, Softail Standard, Heritage Classic, Softail Slim and other compatible M8 Softail models within the listed year range.

2026 Models: Designed to fit the updated 2026 Harley-Davidson Softail platform, including Low Rider ST models with the updated cam cover configuration.

Does Not Fit: Harley-Davidson Breakout or Fat Boy models.

Note: Verify your exact motorcycle model, year, engine combination and exhaust configuration before ordering. Proper tuning is recommended when installing a performance exhaust, particularly on modified or large-displacement engines.

Features

• High-flow performance exhaust for Harley-Davidson Milwaukee-Eight Softail models
• Fits most 2018-2026 M8 Softail applications
• Fits updated 2026 Softail and Low Rider ST models
• Does not fit Breakout or Fat Boy models
• Large 4.5" high-flow rolled-cone muffler
• Stepped internal baffle transitions from 2-1/4" to 2-1/2"
• Designed to improve bottom-to-midrange torque and horsepower
• Can accommodate 88" through 143" engines when properly tuned
• .065" stainless steel header construction
• Stepped headers transition from 1-3/4" to 1-7/8" to 2" at the collector
• Optional Pro Flo Chambers available
• Pro Flo Chambers are designed to aid exhaust reversion and expansion
• Pro Flo option can provide additional torque and horsepower over the standard configuration
• Hand TIG welded from top to bottom
• Machined stainless steel header collars
• 18mm O2 sensor bungs
• Includes 12mm O2 sensor adapters
• Compatible with factory O2 sensors or applicable wideband/autotune sensors
• Complete mounting hardware kit included
• Available in Stainless, Black, Polished, Black ONYX and Platinum finishes
• SP Concepts Part Number: SPC-1-003-ST