270 MX SHOOTOUT: THE OVER-BORES

 
(8/15/2012)
 
Let’s make it clear up front: 2012 has been a great year for 250F riders. All the bikes were amazing in some way. The KTM 250SX-F became the first electric-start 250 motocross bike, the Yamaha got a new frame and more horsepower, the Honda was refined, the Suzuki was still on top of its game, and the new double-injected Kawasaki was flat amazing. Who could ask for more?
We could. It’s our nature. We can’t look at any dirt bike or group of dirt bikes without the wheels turning and plans forming. In the 250F class, horsepower is still the limiting factor. While the typical 450 has more muscle than the average rider can handle, even the best-running 250Fs can benefit from a little more steam. That’s why overbore kits are so popular. In fact, they’re more common than you realize. The guy next to you on the line? Probably a big fat cheater. The guy next to him? Probably a cheater with bad hygiene and a suspicious rash.
We decided to gather the 2012 250Fs one more time to see how they work with oversize pistons and cylinders. We’re not trying to make you into a cheater; we’re just looking for performance for any class. Age classes usually don’t have displacement limits, and as we said before, a really good 270 can be competitive with a 450. But not all the 250s make really good 270s. Some are much better than others. Here’s how the 250s rank when they’re no longer 250s.
 
 
 
FIRST PLACE: HONDA CRF270R
Waking up the red beast
BEFORE THE BORE: Honda has a great 250F, but it’s never been the best. For 2012, the CRF250R got a few changes, including a smaller throttle body and new linkage. Both were improvements. The bike made more low-end power without any real loss on top, and the handling settled down considerably. The Honda’s best feature is that it feels light and easy to handle. Its worst feature is its lack of distinction in the horsepower department. It’s certainly not slow, but horsepower is critical in this class. In our original 250F shootout, the Honda finished fourth.
THE PARTS: As with all the bikes in this story, the key modification was a Cylinder Works big-bore kit, which included a new cylinder, a forged Vertex piston with rings and Cometic gaskets. In this case, the piston was 3.2mm larger than stock, and the final displacement was 270.4cc. The Honda has a single cam, which was replaced by a Hot Cams Stage 2 cam. The pipe was a Factory 4.1 RCT Ti with a Megabomb header. Tokyo Mods reprogrammed the stock ECU to deal with the change in engine spec. The Honda also got a MotoTassinari Air4orce air boot.
RESULTS: Not only was the CRF the most improved of the batch, it was easily the best finished product. It made the most horsepower and had the best power spread, starting way down low and losing virtually no revs on top. We don’t understand why one bike would benefit from a displacement increase so much more than the others. We doubt it’s because the Honda has a 0.2mm-longer stroke, but it might be because of its combustion chamber shape or because the Honda still has a comparatively large throttle body (46mm compared to 43mm on most of the others). Either way, the CRF270R is a rocket. And when you combine that with its already light feel, it’s a great bike.

 .

The Honda starts off with a very large throttle body, so it responds well to an increase in the bore.
 
 

SECOND PLACE: SUZUKI RM-Z270
It pays to use good raw materials

BEFORE THE BORE: Suzuki won our 2012 250F shootout, despite being unchanged since the previous year. For that matter, it also won the 2011 250F shootout, but for different reasons. In 2011, it was the best in every category. It made the best power, had the best suspension and it had the best handling. By 2012, it had been surpassed in all those categories, but not by any one bike. By being so good in so many ways, the Suzuki emerged as a surprising winner. But, it needs attention. If that attention isn’t coming from Suzuki, it might as well come from us.
THE PARTS: The Cylinder Works kit with the Vertex piston gave the Suzuki a 3mm increase in bore, bringing it to 80mm. The Suzuki’s stroke is 0.2mm shorter than the Honda’s, so the end result is 269.4cc. It got both intake and exhaust cams from Hot Cams (Stage 2). For the Suzuki’s EFI system, we looked to Bazzaz because of that company’s close work with Yoshimura and the factory Suzuki race team. The Z-FI kit comes with a fully reprogrammable black box and defaults that have been set up based on extensive dyno testing (presumably on a motor with stock displacement). We installed a Uni filter with the air-filter cage from the Suzuki RM250 two-stroke because it has no backfire screen, and we topped off the motor with a Factory 4.1 RCT Ti muffler and Megabomb header.
RESULTS: When you start off with such a great bike, it’s tough to mess things up. We loved the RM-Z270 just like we loved the RM-Z250. What’s not to love? We started off with a powerful, well-suspended bike and made it more powerful across the board. The extra displacement provided the most benefit right in the middle. There might have been some benefit at the very bottom too, but frankly you never ride that low in the rev range, at least not on a motocross track. On top, the peak power arrived earlier than stock, but the over-rev was fairly long and flat. In other words, if you wanted to stretch a gear without shifting, you could get away with it; the Suzuki wouldn’t fall on its face. In the end, the big-bore kit was a distinct improvement over stock, but the Suzuki didn’t get quite as much benefit as the Honda.
 

Suzuki won our 2012 250 MX comparison after a knockdown, drag-out fight with the Kawasaki. Factory Connection set up the RM-Z’s suspension for our 270 bash.
 
 
THIRD PLACE: KAWASAKI KX270F
A case of diminishing returns

BEFORE THE BORE: The 2012 Kawasaki KX250F was responsible for a war among test riders during our 2012 shootout. It was a greatly improved bike, and without a doubt the fastest of the 250Fs. For some, that was enough to put it in first place. For others, the Suzuki was still number one. In the end, it boiled down to a vote count, but the Kawasaki fans continued to hold their ground. The big news for the 2012 Kawasaki KX250F was the secondary injector upstream of the throttle body that gave it so much additional power. The new Kawasaki also got a rebalanced crank, stiffer spring rates and a rework of the SFF fork with its single spring.
THE PARTS: The Kawasaki, Suzuki and Yamaha all have identical bore and stroke dimensions in stock configuration. After the Cylinder Works barrel, Vertex piston and Cometic parts, they again had the same dimensions. All got a 3.0mm increase in bore to bring the displacement to 269.4cc. The Kawasaki also got both cams replaced with Hot Cams Stage 2 parts and was blessed with a Factory 4.1 RCT Ti muffler with a Megabomb head pipe. Tokyo Mods remapped the ECU using Kawasaki’s programming software. That’s a great option for those who don’t want to buy the stuff from Kawasaki and haul their laptop to the track.
RESULTS: As you might expect, the Kawasaki got an increase in power. It made as much as four horsepower more in the middle and got more at the very bottom, below the normal MX riding zone. In this case, we saw some diminishing returns compared to the others. As a 250, the Kawasaki starts off with more power than any of its classmates, but as a 270, it ended up in the middle of the pack. It lost more revs on the very top, mostly because it had more to lose. It’s a great bike, but it didn’t get the cc-per-cc improvement that we saw in the others.

Kawasaki went into the test with a big horsepower advantage. With big-bore kits, sometimes that makes a difference, sometimes it doesn’t.
 
 

 
FOURTH PLACE: YAMAHA YZ270F
Still the carbureted wonder at any displacement

BEFORE THE BORE: Yamaha came into 2012 without high expectations. It was the only carbureted bike, and that seemed to say that it was behind the times. But, it surprised everyone. Somewhere in its short list of changes, it found more horsepower. It had more snap, more middle and more top. It also got a new frame and was a great-handling bike—thanks in no small part to its weight. It was the lightest 250F by a good margin. In the end, slight carburetion hiccups and the sheer excellence of the Suzuki and Kawasaki put the Yamaha in third place.
THE PARTS: Frankly, we were worried about the Yamaha’s response to a big-bore kit. In the time since the original test, we had discovered the secret behind the increase in power for 2012. It was all attributed to a new piston. We would be taking out the miraculous stock piston and replacing it with something else—albeit something else that had a 3mm size advantage. As it turned out, the 80mm Vertex piston for the Yamaha was also new for 2012. Like the others, the YZ got two Hot Cams Stage 2 cams, although it should be noted that the intake side is more expensive than the others because it has an extra lobe to deal with Yamaha’s fifth valve. The YZ makes up for that by needing no remapping, only a few jets (170 main, 42 pilot, 60 leak). The YZ also got a Factory 4.1 RCT Ti Muffler with a Megabomb header and a two-stroke filter cage with a Uni filter.
RESULTS: All our piston worry was for nothing. The YZ270F got a uniform improvement throughout the powerband. As with the other bikes, the biggest gain was right in the middle of the powerband. The point at which peak power occurred was lower than stock, but not dramatically so. The finished Yamaha was actually slightly more powerful than the Kawasaki 270, but it didn’t quite have the peak output to match the Honda or Suzuki 270s.

 .

Yamaha gave its YZ250F a new piston and a lot more power for 2012. Could a 270 kit be any better? Our 270 test bike had its suspension set up by MB1.
 

FIFTH PLACE: KTM 275SX-F
More current for the electric soldier

BEFORE THE BORE: KTM’s 2012 250SX-F is like nothing in its class. It started life as an off-road bike in 2011 and was brought into the MX world as the only electric-start 250F available. The starter and battery resulted in a weight penalty—the KTM was almost 10 pounds heavier than any of the other bikes. An even bigger problem was the power output. The KTM still ran like an off-road bike, with slow revs and unsensational peak output. It was an impressive bike in many ways, but it wasn’t a great motocrosser.
THE PARTS: All the Cylinder Works big-bore kits that we used in this shootout make use of an 80mm piston. That gave the KTM a nice little bonus. It started off with a 76.0mm by 54.8mm configuration, so the 80mm piston represented a bigger increase, percentage-wise. The KTM’s final displacement was 275.5cc. As on the other double-overhead-cam machines, we installed two Hot Cams Stage 2 cams.
Most recent KTMs have two different ignition maps in their electronic brains. We ran the aggressive map from 2011 along with a MotoTassinari Air4orce intake boot and a Factory 4.1 RCT Ti muffler with a Megabomb header. Since one of the real issues facing the KTM is weight, we couldn’t walk away without shaving off at least a couple of pounds. CV4 makes a lithium-ion battery that does just that.
RESULTS: We achieved a completely unintended result with the KTM 275: we built an incredible off-road bike. It gained power everywhere, but the best part was way down low. Again, this isn’t necessarily anything you would notice on the motocross track, but it made the bike much easier on the trail. The KTM still has a comparatively slow-revving motor, and that makes it feel sleepy on the track. It’s interesting to note that for next year KTM has a new 250SX-F motor with a different bore-and-stoke configuration. Instead of having the longest stroke in the class, it will have the shortest. This bike will still be available in the XC-W version, and you can rest assured that many of those will become 275s

KTM has the only electric-start 250F motocross bike. That’s good, but the weight penalty isn’t. Race Tech handled the KTM’s suspension duties.
 
 
 

CONTACTS
Bazzaz Performance: www.bazzaz
.net; (909) 597-8300
Cometic Gasket: www.cometic.com; (800) 752-9850
CV4: www.cv4.net; (800) 874-1223
Cylinder Works: www.cylinder-works.com; (515) 251-4070
DeCal Works: www.decalmx.com; (815) 784-4000
Dunlop Tire: www.dunlopmotor
cycle.com; (800) 845-8378
Factory Connection: www.factory
connection.com; (866) 220-1151
FMF Racing: www.fmfracing.com; (310) 631-4363
Hinson Clutch Components: www.hinsonracing.com; (909) 946-2942
Hot Cams: www.hotcamsinc.com; (515) 402-8200
MB1 Suspension: www.mb1
suspension.com; (951) 371-5045
Moto Seat: www.motoseat.com; (951) 258-5229
Motosport Outlet: www.moto
sport.com; (888) 676-8853
MotoTassinari: www.mototassinari
.com; (603) 298-6646
Race Tech: www.racetech.com; (951) 279-6655
Renthal: www.renthal.com; (877) 736-8425
Tokyo Mods: www.tokyomods.com; (888) 457-9403
Uni Filter: www.unifilter.com; (714) 535-6933
Works Connection: www.works
connection.com; (800) 895-8292
 
 
 
 
Comments:
Thursday, August 16, 2012 6:45:38 PM by PDR Motorsports
UPDATE i posted earlier about the big bore kits that they failed, this is the deal. from 2005-2009 the stroker kit and the big bore kit used together is not the best idea it its going to be raced . the angle of the rod is so great it puts to much pressure on the skirt and can couse it to break. but if you use eather the stroker or just the big bore you should be fine. C & L stepped up to the plate a warranteed our motors . AGAIN this is only on the 2005-2009 crf 250, thank's to jay clark and to steve depping. this warranty was taken care of, Douglas Keltner @ PDR Motorsports
-----------------------------
Douglas Keltner

Leave your comment
 
You must sign in to post
 
Username 
Password 
No Blogger account? Sign up here.
CAPTCHA Validation
Retype the code from the picture
CAPTCHA Code Image
Speak the code Change the code
 

Topic: col 1

News:
  • ADJUSTING TO STADIUM RACING


 

ON SALE NOW
 
Subscribe

- Inside This Issue

- Contact
- Advertise
- Back Issues







 
WARNING: Much of the action depict­ed in this magazine is potentially dan­gerous. Virtually all of the riders seen in our photos are experienced ex­perts or professionals. Do not at­tempt to duplicate any stunts that are be­yond your own capabilities. Always wear the appropriate safety gear.

Copyright 2008 Hi-Torque Publications, Inc. All rights reserved.
Console Login