PHOTOGRAPHY BY KIT PALMER

Whats the biggest advantage of the Cylinder Works 270cc big-bore kit for the Honda CRF250R  Torque!

What’s the biggest advantage of the Cylinder Works 270cc big-bore kit for the Honda CRF250R? Torque!

There is a reason why big-bore kits are so popular with 250Fs these days. Actually, there are many reasons: They boost engine performance big-time, they make riding 250Fs a lot more fun, they are relatively simple to install (if you know what you’re doing or know someone who does and is willing do the work for you, then it’s really simple), and they are far cheaper to buy than a new bike. And for many, big-bore kits are the answer to 450s that are just too much and 250Fs that are not big enough. As a results, 250F big-bore kits have become very popular with the veterans who don’t need 450 power but want a little more oomph and torque than a stock 250F for racing in the vet division, where classes are usually determined by age, not engine size. Big-bore kits are also very popular with pros who want a practice bike that mimics the power output of their heavily modified 250cc race bikes and want something that will last a lot longer than their highly-strung race engines. And, of course, big-bore kits are also popular with cheaters. (You know who you are and, yes, we hope you have trouble sleeping at night.)

We can definitely vouch for the fun part. Big-bore kits for 250Fs are a kick in the pants and we were reminded of this recently after spending a day at Starwest Cycle Park on a very pumped-up 2014 Honda CRF250R that was fitted with a Cylinder Works 270cc big-bore kit (and more). So much fun!

The ultimate vet bike  Our CRF270F has plenty of advantages vet riders will like over a 450.

The ultimate vet bike? Our CRF270F has plenty of advantages vet riders will like over a 450.

In the $650 Cylinder Works box you’ll find a very stock-looking cylinder, a 3.2mm larger forged Vertex piston (complete with rings, circlips and wristpin), and a Cometic top-end gasket kit. Once installed, your CRF250R is now technically a CRF270.4R.

The Honda we rode was also fitted with a Hot Cams stage-two camshaft, something our Cylinder Works representative said isn’t completely necessary to run with the big-bore kit but well worth the extra $270 if you want to take full advantage of the CW big-bore kit. Our CW rep told us that the CRF250R gains three horsepower and about three ft. lb.of torque with the 270 big-bore kit alone.

To increase those numbers a little further, however, our CRF250R was also fitted with an aftermarket exhaust system, in this case, FMF’s dual Factory 4.1 RCT Ti Muffler and Ti Megabomb header. Again, not a must-have addition, but… what the heck. If you’re going this far – and most people do – a pipe is a natural mod. He did, however, highly recommend fitting the big-bore kit with a better-breathing air boot. After all, more power means more air is needed to feed the combustion chamber, so an Air4orce air boot from MotoTassinari was installed.

Other mods that were incorporated into this bike were a Vortex (X-10 ECU) ignition, and minor modifications to the bike’s throttle body that were accomplished by Injectioneering.

The Cylinder Works big-bore kit is enhanced greatly by a few more bolt-on additions  like a pipe  cam and a larger air boot.

The Cylinder Works big-bore kit is enhanced greatly by a few more bolt-on additions, like a pipe, cam and a larger air boot.

The main goal of the 270 big-bore kit our rep said wasn’t so much about increasing total, or peak, horsepower as it was “boosting torque and getting the torque to start a little earlier [in the powerband] and lasting a lot longer. Any other mods, like modifying the throttle body and ignition, he said, are only done to improve throttle response and to give the rider a better overall experience.”

By the time all the motor mods were completed with our bike, horsepower had been increased to five and torque to four ft.-lbs., according to the CW rep.  

The end result? A really fun-running CRF250R. Veteran Cycle News test rider Jason Abbott was very impressed with the bike, saying he could easily notice the stronger bottom-end power and increased and broader torque. “They were significant,” he said.

The heart of the CW big-bore kit -  650 will get you a new cylinder  piston and top-end gasket kit.

The heart of the CW big-bore kit - $650 will get you a new cylinder, piston and top-end gasket kit.

The 2014 Honda CRF250R already made decent power overall, especially in the first half of the powerband, but nothing like this. The increased displacement of the 270cc kit was again extremely noticeable and very welcomed.

At first, Abbott did not feel much of a benefit on top, but the more he rode the bike, the more he began to notice a difference. “You really have to get on it and let it rip on top before you start noticing it,” Abbott said. “It’s just that when you rev it out like you normally would on the stock bike it feels about the same, but then you realize there is more, and that’s when it really kicks in.”

Stock gearing is a little too low for the 270 kit, so we swapped out the stock 49-tooth rear sprocket for a 48T, which helped make the bike pull smoother out of the turns and better place the shifting points. Abbott, however, said that he would even consider gearing it up a little further to a 47T for longer tracks, saying that he felt the Honda would not have problems at all pulling the taller gearing.

The 270-kitted CRF250 we rode didn’t sound all that much different than a stocker with a modified exhaust, just a really good running one, so you ethically challenged racers out there will like that. But everyone will appreciate the fact that you don’t have to run high-priced race gas with the 270 big-kit, as it was specifically designed to work well with no less than 91-octane pump gas.

With the 270 big-bore kit installed  the Honda gets big-bike-like power while retaining its much-liked 250F characteristics.

With the 270 big-bore kit installed, the Honda gets big-bike-like power while retaining its much-liked 250F characteristics.

So, can the 270 Honda compete against 450s in the vet class? For sure, but more so on tight and rough tracks than on fast, smooth and hilly tracks. You’ll last a lot longer on the rough tracks and have more fun doing so. Abbott also said that he thought the 270 would make a great off-road bike because of the increased bottom-end and torque.

No one said racing dirt bikes is cheap and neither are these mods. There’s no hiding that fact. We figure our CRF270R had at least $2000 worth of mods done to the engine alone, but if you’re willing to spend that kind of money, we think you’ll be happy. For how long, though, we don’t know, but we have no reason to believe that this kitted Honda won’t last a long time. The CW 270 big-bore kits do seem to be well built, however, and the Iowa-based company has a very good reputation. And if you’re wondering, Cylinder Works makes big-bore kits for all of the Japanese 250F motocrossers, new and many old.

For more information, visit www.cylinder-works.com, www.hotcamsinc.com, www.vortexcdi.com, www.injectioneering.com, www.mototassinari.com and www.fmfracing.com.

By Cycle News Staff

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