301cc Complete Big Bore Kit

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Originally developed for my racing endeavors on a CBR300R, this kit has dozens of race wins, two class championships, and one lap record to its credit. With tens of thousands street and off-road miles logged, this is a proven and reliable setup for improving your CRF's performance, capability, and fun factor.

This piston and cylinder kit turns your CRF300L into a true 300 with an additional 14.8cc while also increasing compression from the stock 10.7:1 to 11.5:1. When combined with the required Stage 3.0 parts which include a high-flow air filter, hi-flow velocity stack, CBR cams, performance exhaust, and Stage 3.0 ECU tune, you get a massive increase in torque (+25%) and horsepower (+34%). Throw on a CNC ported cylinder head and Stage 3.5 ECU tune for even more gains (+30% torque and +39% horsepower). 

To ease installation, we now pre-set ring gap, install and orient the rings on the piston, install the right (cam-chain side) wrist-pin circlip, lubricate the piston and cylinder, and then slot the piston into the cylinder.  This greatly reduces the work required for installation; just drop the whole assembly onto the con-rod, install the left circlip, and press the cylinder down. 

With our 301cc piston kit and full Stage 3.0 parts package you can expect faster acceleration, snappier throttle response, and easier highway cruising. See dyno charts and performance comparison below.  

This piston and cylinder kit includes: 

• Forged 78mm piston, 11.5:1 compression ratio
• Piston ring set, properly gapped
• Wrist pin and circlips
• New, OEM Honda cylinder bored to match piston
• Cometic head and base gaskets in custom thickness to optimize quench clearance
• Upgraded Class 10 stud nuts
• Click here for install tips and break-in guidelines

PLEASE NOTE: This is not a standalone mod! You must run the full Stage 3.0 parts package and ECU tune. 91 octane (R+M)/2 (95 RON) gas is required. This kit should be installed by a professional mechanic or someone of similar experience following steps outlined in a service manual. 

Warning: This product is for closed-course competition use only and is not intended for street use or use on public lands. This product is not legal for sale or use in California.