Description
D&D 638Z-31B Fat Cat Black 2-into-1 Exhaust for 2018-Newer Harley M8 Softail Wide Tire Models
The D&D 638Z-31B Fat Cat Black 2-into-1 Exhaust for Harley M8 Softail Wide Tire models delivers aggressive tone, strong low-end torque, and bold Fat Cat styling.
Specifically designed for 2018-newer Breakout and Fat Boy Milwaukee-Eight (M8) Softail models, this system gives wide-tire bikes the performance they deserve. However, it does not fit Street Bob, Low Rider, Slim, Fat Bob, Deluxe, Sport Glide, or Heritage Classic models. Instead, those models require part number 634Z-31B.
At its core, the Fat Cat uses a stepped 2-into-1 header to increase exhaust velocity and improve throttle response. As a result, you get stronger bottom-end pull and smoother power through the RPM range. The stepped design transitions from 1 3/4″ to 1 7/8″ to 2 1/8″ at the collector, and then flows into a 2 1/2″ muffler connection.
In addition, this full M8 Softail system includes heat shields, exhaust gaskets, and mounting hardware. The 4″ muffler housing features a louvered performance baffle and a back-cut tip, giving your bike that deep, aggressive Fat Cat sound.
For tuning flexibility, the system includes both 18mm and 12mm O2 bungs. Because of that, you can easily pair it with an auto-tune module like ThunderMax AutoTune for precise fuel control. Ultimately, this exhaust increases horsepower while delivering the torque you feel right off the line.
Fitment
✔ 2018-Newer Harley M8 Softail Breakout
✔ 2018-Newer Harley M8 Softail Fat Boy
❌ Does NOT fit:
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Street Bob
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Low Rider
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Slim
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Fat Bob
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Deluxe
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Sport Glide
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Heritage Classic
Key Features
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Stepped 2-into-1 header design
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1 3/4″ → 1 7/8″ → 2 1/8″ primaries
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4″ Fat Cat muffler housing
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Louvered performance baffle
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Back-cut exhaust tip
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Heat shields included
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18mm & 12mm O2 sensor bungs
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Hardware and gaskets included
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Built to increase torque and horsepower
