Description
🔧 CSR 128″ High Compression Big Bore Kit for Harley M8
The CSR 128″ High Compression Big Bore Kit is one of the best cylinder kits available for the Harley-Davidson M8 platform. This kit increases displacement from 114″ or 117″ to a full 128″, making it an ideal upgrade for riders who want more power while continuing to use their existing camshaft.
In addition, head work is not required for installation. However, you may choose to add port work later as your build evolves.
📦 What’s Included in the Kit
This complete big bore package includes everything needed for a top-end upgrade:
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Cylinders
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Forged pistons
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Piston rings
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Head gaskets
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Base gaskets
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Top-end rocker box gasket kit
As a result, this kit is a straightforward solution for riders looking to increase displacement and compression without unnecessary complexity.
⚙️ Camshaft Compatibility
The CSR 128″ High Compression Big Bore Kit pairs exceptionally well with the following cams:
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Zipper’s Red Shift 528 Cam
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Zipper’s Red Shift 532 Cam
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Zipper’s Red Shift 548 Cam
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Zipper’s Red Shift 552 Cam
Additionally, this kit works with other bolt-in Gen 2 M8 camshafts, giving builders flexibility when planning their setup.
➕ Optional Add-Ons (Recommended)
To maximize reliability and performance, consider adding the following components:
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Feuling 3007 ARP Head Bolt Kit or S&S 900-1006 Head Bolt Kit
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CSR 70mm Throttle Body
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Zipper’s 7.1 GPS High-Flow Injectors
These upgrades support higher airflow, improved fuel delivery, and long-term durability.
🇺🇸 American-Made Quality & Engineering
The CSR 128″ Big Bore Kit is 100% American-made and manufactured by the same company that produces our 139″, 144″, 147″, and 153″ engine kits.
First, we start with premium cylinder cores. Then, we bore them out, remove the original steel liner, and install our proprietary ductile iron sleeves. This high-tensile material allows the sleeves to remain straight and round, which creates an ideal ring seal when paired with Total Seal piston rings.
Furthermore, the pistons are forged aluminum and built to our exact specifications. We also use tool-steel wrist pins to ensure maximum strength and durability. Every big bore kit includes Cometic gaskets, which are trusted for high-performance applications.
📐 Technical Specifications
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Bore Size: 4.25″
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Compression Ratio: 12.3:1
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Piston Design: Domed (not flat-top)
This domed piston design raises compression significantly, which improves torque and throttle response across the RPM range.
