Description
D&D 634Z-31B Fat Cat 2-Into-1 Exhaust
For 2018-Newer Harley-Davidson® M8 Softail Models
If you want stronger torque and a deep, aggressive sound, the D&D 634Z-31B Fat Cat delivers. Designed specifically for Milwaukee-Eight Softails, this 2-into-1 system improves throttle response while adding serious performance gains.
Plus, it fits models equipped with either mid or forward controls, making it a versatile upgrade.
✅ Fits These M8 Softail Models:
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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
However, this system does not fit the Breakout or Fat Boy. Instead, use the D&D 638Z-31B for those models.
🔧 System Specifications:
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Stepped headers: 1 3/4″ → 1 7/8″ → 2 1/8″
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2 1/2″ collector
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4″ muffler body
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Louvered baffle
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Back-cut tip
As a result of the stepped header design, the Fat Cat improves exhaust scavenging and boosts low-end torque.
📦 What’s Included:
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Complete exhaust system
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Heat shields
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Exhaust gaskets
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Mounting hardware
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Bolt kit
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Baffle
Therefore, you get everything needed for installation right out of the box.
⚙️ Tuning Ready
Additionally, the system includes both 18mm and 12mm O2 bungs. Because of this, you can easily run wideband tuning modules like ThunderMax Auto Tune.
In short, the D&D Fat Cat adds horsepower, increases torque, and gives your M8 Softail the performance edge it deserves — all while delivering that unmistakable D&D sound.
