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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 big-bore kit turns your CRF300L into a true 300 with an additional 14.8cc of displacement and bumps compression from the stock 10.7:1 to 11.5:1. When combined with the required 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).
Expect faster acceleration, snappier throttle response, and easier highway cruising. See dyno charts and performance comparison below.
This is a complete and comprehensive kit that 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
This kit should be installed by a professional mechanic or someone of similar experience following steps outlined in a service manual. Proper ECU tuning and 91 octane (R+M)/2 (95 RON) gas is required. We offer 550 Performance ECUs and also have PowerVision flashes available.
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.
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.
I was considering selling my 2022 CRF 300L for a year or so. I had considered the big bore kit bebofore, but was not comfortable to do the install myself. I also live on the east coast and was not wanting to ship anything to Ari out in California. Ari saw a comment I had made on the CRF 300L Facebook group about wishing there was a qualified mechanic on the East Coast, and replied that he knew of somone.....not only did he get me connected to him, but he quickly shipped out the complete kit and all required components, and introduced me to the mechanic. The kit and professional installation made the CRF 300L a bike that I love to ride. I highly recommend the kit, and consider working with Ari on finding a qualified mechanic!B
Just an average rider at 64, I didn't really need a super-fast bike. The bike was running well. And the most I'd done was install a Yoshi, an LED headlight, and replace the ECU. The YouTube videos were daunting - no way I could put all that back together again, properly. But I needed a project, and as soon as I'd dismiss it it would pop back into my head. Maybe doing the work myself would add some measure of legitimacy to my motorcycle hobby.
I was slow taking the bike apart, terrified I'd break something. Tricky disconnects on fuel and various electrical connections were challenging. And one nearly-inaccessible screw after another. I kept Ari (too) busy with questions. He was very patient and helpful. Got the velocity stack installed into the airbox. Got the head and cylinder off. Ari had loaded the piston into the cylinder but it fell out when I was removing the wrist pin. Took all morning to install the circlip. Fashioned a ring compressor by cutting a band of stiff plastic from a peanut butter jar approx piston diameter. Still couldn't get piston into cylinder by myself. Fortunately I have a neighbor at my apts who races bikes and used to be a mechanic. He came over with zip-ties to hold the band in place we tapped the cylinder down over it. So now just put the head on, the cams in, and button it up. Easy, right? Putting the head on w/one set of hands is difficult - what with the gasket, dowel pins, and the cam chain tensioner. But I got it on. In Ari's video he manages this without removing the coolant expansion tank assembly, but I had to remove all that. Then I couldn't fit the second cam in. Chain too tight. Figured the chain dropped off the sprocket and picked back up on the wrong link (impossible in retrospect). Took head back off, chain looked okay. Reinstalled it. Same problem. Ari had never heard of such and wasn't sure what I'd done, but he was trying to help. Finally he asked if I'd torqued the head down. No. Feeling stupid but relieved, I began to put the washers and nuts on the stud bolts. The washer sounded like a quarter going into a Coke machine as it fell out the side hole down into the cam chain compartment. (Don't do that). So close to finishing, then that. My mechanic friend was there. We couldn't see the washer w/phone lights. He suggested taking head and cylinder back off to look for it. Took them off and still couldn't see it. Probably in the bottom of the crankcase. Total dejection. Whole project down the drain. No way to get it out but take it to a shop and let them split the crankcase. Then he took my good shop light and looked down. Saw it. Fetched it out w/magnet. Whew. Put the cylinder and head back on. Buttoned up engine the next day and started putting the bike back together. Took another week. The bike cranked right up. No warning lights.
To now... Just changed out the break-in oil after 100 miles. Only one small coolant leak from not tightening a hose clamp enough. Very happy it looks like a successful install.
The bike runs great and is quicker, but it's hard to quantify. Mostly glad I did it because now I understand more about the motorcycle - the secondary air system, all the hoses, cables, drains, etc. But I couldn't have done it without all the help from Ari, my mechanic friend, and Facebook expert Ace. I bought the Cyclepedia Manual, but the standard service manual was an excellent source of info.
I bought the complete package, and I'm extremely happy with the results. Ari answered all my questions promptly and provided detailed information about the package, including break-in procedures. The bike performs really well and meets all my expectations and beyond. Thank you!
Excellent products
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.
I was considering selling my 2022 CRF 300L for a year or so. I had considered the big bore kit bebofore, but was not comfortable to do the install myself. I also live on the east coast and was not wanting to ship anything to Ari out in California. Ari saw a comment I had made on the CRF 300L Facebook group about wishing there was a qualified mechanic on the East Coast, and replied that he knew of somone.....not only did he get me connected to him, but he quickly shipped out the complete kit and all required components, and introduced me to the mechanic. The kit and professional installation made the CRF 300L a bike that I love to ride. I highly recommend the kit, and consider working with Ari on finding a qualified mechanic!B
Just an average rider at 64, I didn't really need a super-fast bike. The bike was running well. And the most I'd done was install a Yoshi, an LED headlight, and replace the ECU. The YouTube videos were daunting - no way I could put all that back together again, properly. But I needed a project, and as soon as I'd dismiss it it would pop back into my head. Maybe doing the work myself would add some measure of legitimacy to my motorcycle hobby.
I was slow taking the bike apart, terrified I'd break something. Tricky disconnects on fuel and various electrical connections were challenging. And one nearly-inaccessible screw after another. I kept Ari (too) busy with questions. He was very patient and helpful. Got the velocity stack installed into the airbox. Got the head and cylinder off. Ari had loaded the piston into the cylinder but it fell out when I was removing the wrist pin. Took all morning to install the circlip. Fashioned a ring compressor by cutting a band of stiff plastic from a peanut butter jar approx piston diameter. Still couldn't get piston into cylinder by myself. Fortunately I have a neighbor at my apts who races bikes and used to be a mechanic. He came over with zip-ties to hold the band in place we tapped the cylinder down over it. So now just put the head on, the cams in, and button it up. Easy, right? Putting the head on w/one set of hands is difficult - what with the gasket, dowel pins, and the cam chain tensioner. But I got it on. In Ari's video he manages this without removing the coolant expansion tank assembly, but I had to remove all that. Then I couldn't fit the second cam in. Chain too tight. Figured the chain dropped off the sprocket and picked back up on the wrong link (impossible in retrospect). Took head back off, chain looked okay. Reinstalled it. Same problem. Ari had never heard of such and wasn't sure what I'd done, but he was trying to help. Finally he asked if I'd torqued the head down. No. Feeling stupid but relieved, I began to put the washers and nuts on the stud bolts. The washer sounded like a quarter going into a Coke machine as it fell out the side hole down into the cam chain compartment. (Don't do that). So close to finishing, then that. My mechanic friend was there. We couldn't see the washer w/phone lights. He suggested taking head and cylinder back off to look for it. Took them off and still couldn't see it. Probably in the bottom of the crankcase. Total dejection. Whole project down the drain. No way to get it out but take it to a shop and let them split the crankcase. Then he took my good shop light and looked down. Saw it. Fetched it out w/magnet. Whew. Put the cylinder and head back on. Buttoned up engine the next day and started putting the bike back together. Took another week. The bike cranked right up. No warning lights.
To now... Just changed out the break-in oil after 100 miles. Only one small coolant leak from not tightening a hose clamp enough. Very happy it looks like a successful install.
The bike runs great and is quicker, but it's hard to quantify. Mostly glad I did it because now I understand more about the motorcycle - the secondary air system, all the hoses, cables, drains, etc. But I couldn't have done it without all the help from Ari, my mechanic friend, and Facebook expert Ace. I bought the Cyclepedia Manual, but the standard service manual was an excellent source of info.
I bought the complete package, and I'm extremely happy with the results. Ari answered all my questions promptly and provided detailed information about the package, including break-in procedures. The bike performs really well and meets all my expectations and beyond. Thank you!
Excellent products