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Honda posted by

Before & After – 2019 Honda Grom 300cc Build

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2019 Honda Grom 300cc Swap

One of the comical benefits of browsing the internet for motorcycles (or really any vehicle) is that you get to see some custom work that should have been killed in the brainstorming stage. Sometimes you get to see some really good custom work and you can’t help but be envious of the level of skill possessed by the craftsmen. Then you have bikes like this 300cc (250cc + the big bore) Grom Swap. While it’s nothing  I’d ridicule, I imagine something like this falls in the middle of the Venn Diagram for good and bad custom builds. I have so many questions.

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Bolting large engines into the Honda Grom is not a novel idea. A few companies make swap kits and a quick Youtube search yields a lot of interesting videos. The CBR250R swap is the most common since it also employs a single cylinder setup and therefore requires no frame modifications.This builder has gone a step further and tacked on another 50ccs of bore with a Chimera kit. Additional engine mods include a larger throttle body, upgraded cams, and an engine tuner. There aren’t any estimated hp numbers in the listing but a CBR250R makes mid-30s and the cams add about 4 hp per the DCR site. Add the big bore kit, tuner, and throttle body and you’re probably looking at mid 40s to the crank? Frankly, the hp number could just say “Too Fast” and that should send the right message.

One of the more concerning aspects of the build is the amount of torque and stress going through the chassis. More weight from the engine and more speed are going to push this bike out of the intended performance envelope. Don’t be fooled by the aluminum frame covers. The stock steel tube frame lives underneath. All of that being said, the goal was probably not to build a 1:2 scale Fireblade from a performance standpoint so we can’t hold it at gunpoint for that reason.

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The attention to detail on the aesthetic is what really stands out here. You’ll dismiss it as yet another liter bike if you are scrolling too quick. The builder seems to have spared no expense. The only thing the cockpit seems to share with a stock Grom is…nothing?

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If Honda ever wanted to slap Ohvale around in the mini-race bike market they should call this guy. he might be able to save them a couple bucks in R&D. Start to finish this Grom (if you can even call it that) looks great.

Bike does not have Ohlins suspension! Just stickers . Bike does not have an Akrapovic exhaust ! Just sticker , It is all stainless exhaust . 84mm 12.5 comp piston and new cylinder kit , 42mm Throttle body, 6 disc clutch pack , over size injector , custom aluminum 90 degree intake for proper placement of the injector . complete ARacer 5 computer system with data logger , the ARacer system is completely adjustable from an app on my phone . Speedo correction link , hydraulic clutch kit , lithium battery, DCR S2 cam shaft kit with springs and valves , new cam chain and solid tensioner . All the bolts for the engine are titanium and many on the bike are also . The body kit is from Thailand and is all fiberglass, there are some nicks scratches and cracks . It’s good but not perfect . You can see all the rest of the parts installed . The Grom had under 300 miles when I started this build.

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As cool as this build is, the reason it has to live in the middle of the Bad & Good Build Venn Diagram is the price… After seeing all the parts and quality of the finish I fully believe the seller spent a small fortune putting this together. The frame, forks, and rims may be the only stock parts on the whole bike. Unfortunately the old adage says a custom build is always worth far more to the builder than the buyer… Unless you’re Jesse James. In that case the first owner get’s raked over the coals. I don’t mean take any credit away from the build. From design to execution, this guy has hit the mark. I’d bet one would spend more time looking at this at a museum or bike meet than some of the other high dollar attendees.

Thanks for reading!




  • During the initial write up of this bike, the price was ~$13K. The seller has since lowered to $10K.

  • O, ithink that shock is ohlins…. And when you add this much weight, a grom fork absolutely needs heavier springs and an ohlins cartridge insert in the fork. If not, you will die the first time you graze the brake lever. Even though that stock brake will require a fore arm like Popeye to function adequately.

    These shortcomings aren’t anything a weekend and $500 can’t fix…

  • Whoa, this bike is 2 hours from me, I also happen to have my trailer with me…. I’m visualizing that if I leave now by this afternoon I could be on the banks of daytona. Shake-n-Bake Ricky Bobby!

  • I know people seem to love groms but I don’t fancy being about bumper high. In today’s suv filled world and those small tires will get you into trouble with them faster speeds heavier engine. No thanks rather just buy a cbr 300.

    I think it be more fun as a dual sport setup just street legal enough for road use. Off road enough to maybe poach trails. With a quiet style performance exhaust on that 300.

  • @Ericandchi you would also be the most popular person at the bike meets.

    @SmokinJoe90 This would be best served as parking lot track weapon for me.

  • LOL, some people have way too much time and money on their hands these days.

  • Isn’t that the dream?

  • Google the words “gokart track” in your area. 🙂 groms don’t shine as streetbikes, IMO.

  • Need to sell my Honda rs125r I made street legal when I was bored , if he gets $10k .

  • @Norm as mentioned, Groms are best enjoyed at the track. I raced mine for a year. Now it gets trailered with my wife’s Grom where we only do mountain roads like blue ridge parkway. Then the risk of getting run over by a semi or SUV is reduced. I did however have a good run one day with my buddy in Texas hill country…him on an RSV4, me on the Grom. He stopped to play solitare at the end of the long straights while waiting for me.

  • Should have thrown in some sort of 2 stroke engine. These Grom swaps are pretty common and there are drop-in kits for the CBR250 and 300 engines.

  • Is its Cali plated? I’ve only seen one plated driving in downtown Berkeley @15yrs ago. Interested if you’re truly going to sell. Very.

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