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301cc Complete Big Bore Kit
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.
Nice complete kit. Prompt service. Have not installed yet, but can't wait.
Thanks Ari! Bike feels phenomenal! If you’re on the edge of deciding whether to upgrade or not, do it!! Not one regret, only wish I could ride everyday!
This kit does wonders for the 300 platform. Do set huge expectations as far crazy power. What you do get is usable power through the whole rev range now. 3rd and 4th gear are phenomenal! My bike will pull 6th gear up a hill now. You don't have downshift as much before a turn to be able to power out of it. I did the install myself with no issues. Ari is great at answering any questions or concerns in a very timely manner. I would definitely recommend this to any on the fence about doing it. You will not regret it. I would do agian in a heart beat.
Before Ari’s 301 kit, my CRF300L was a polite trail companion—reliable, but a bit… apologetic. Now? It’s got guts. Real, grin-inducing, pass-with-confidence, torque-down-low guts. Highway on-ramps? Bring ‘em. Uphill climbs? Laughable. It pulls harder, revs happier, and honestly, just feels like it finally woke up and chose violence—in the best way.
The fun factor? Off the charts. It didn’t just add power—it added personality.
And let’s talk about Ari: this guy’s customer service is as dialed as his kits. Generous with his time, patient with questions, and genuinely invested in making sure your install and setup go smooth. Seriously, he couldn’t have been more helpful or accommodating—like having a tuning guru in your pocket.
Bottom line: If you’ve got a CRF300L and don’t get this kit, you might need your head examined. This is the upgrade Honda forgot to give us. Ari didn’t.
This kit brings the rest of the goodies to life. The pipe, the tune, intake mods all work better because of this 301 kit. Thanks for the ambition, and ingenuity in developing this kit for sale. I have built plenty of small engines for karting, but never have I built a four stroke motorcycle engine. Only one small issue that was resolved before startup and it has been a smile maker ever since. I have about 400 miles on it so far, mostly two track stuff, and I love it. This kit gives the ability actually power out of a corner, with a smile! Everything went off without a hitch as far as product order and delivery. Piston is installed into the cylinder and if you are careful it all goes together real nice. All the correct gaskets included, what's not to love? I would suggest having shims on hand before you get the Big Bore kit so you don't have to wait on them.
Ari, thank you so much for putting this together for us. I couldn't be happier to have pulled the trigger on this kit.
Nice complete kit. Prompt service. Have not installed yet, but can't wait.
Thanks Ari! Bike feels phenomenal! If you’re on the edge of deciding whether to upgrade or not, do it!! Not one regret, only wish I could ride everyday!
This kit does wonders for the 300 platform. Do set huge expectations as far crazy power. What you do get is usable power through the whole rev range now. 3rd and 4th gear are phenomenal! My bike will pull 6th gear up a hill now. You don't have downshift as much before a turn to be able to power out of it. I did the install myself with no issues. Ari is great at answering any questions or concerns in a very timely manner. I would definitely recommend this to any on the fence about doing it. You will not regret it. I would do agian in a heart beat.
Before Ari’s 301 kit, my CRF300L was a polite trail companion—reliable, but a bit… apologetic. Now? It’s got guts. Real, grin-inducing, pass-with-confidence, torque-down-low guts. Highway on-ramps? Bring ‘em. Uphill climbs? Laughable. It pulls harder, revs happier, and honestly, just feels like it finally woke up and chose violence—in the best way.
The fun factor? Off the charts. It didn’t just add power—it added personality.
And let’s talk about Ari: this guy’s customer service is as dialed as his kits. Generous with his time, patient with questions, and genuinely invested in making sure your install and setup go smooth. Seriously, he couldn’t have been more helpful or accommodating—like having a tuning guru in your pocket.
Bottom line: If you’ve got a CRF300L and don’t get this kit, you might need your head examined. This is the upgrade Honda forgot to give us. Ari didn’t.
This kit brings the rest of the goodies to life. The pipe, the tune, intake mods all work better because of this 301 kit. Thanks for the ambition, and ingenuity in developing this kit for sale. I have built plenty of small engines for karting, but never have I built a four stroke motorcycle engine. Only one small issue that was resolved before startup and it has been a smile maker ever since. I have about 400 miles on it so far, mostly two track stuff, and I love it. This kit gives the ability actually power out of a corner, with a smile! Everything went off without a hitch as far as product order and delivery. Piston is installed into the cylinder and if you are careful it all goes together real nice. All the correct gaskets included, what's not to love? I would suggest having shims on hand before you get the Big Bore kit so you don't have to wait on them.
Ari, thank you so much for putting this together for us. I couldn't be happier to have pulled the trigger on this kit.