SR Archive: Ontario Moto-Tech 161-mph Honda CBR600F2

This article was originally published in the October 1995 issue of Sport Rider.

After winning the '92 WERA 24-Hour West (with the support of Honda and its roadracing teams) and developing his CBR900RR Sport Rider project racer into one of the best CBR9s in the country, Ontario Moto-Tech's Kaz Yoshima did what he does most often: He became bored. Nothing bores Kaz more quickly than getting a bike right. It was time for a new challenge: something different, something smaller and lighter, something he could really make scream.

How about grabbing a beaten and battered '91 CBR600F2 from Honda's test fleet and turning it into a racetrack ripper that's quicker and faster than a stock CBR900RR? That sounded like fun, so we signed up for the ride. Luckily, so did American Honda's Dirk Vandenberg and Gary Christopher. It took more than a few months of development, but the Ontario Moto-Tech machine has met or exceeded all its design objectives: a best quarter-mile blast of 10.48 seconds at a blistering 131.9 mph and a liter-bike–league 161-mph top speed—now that's a screamin' 600.

The Engine
Yoshima's engine-building theories come from three decades of experience, dating back to his days at Honda Japan in the '60s. When Yoshima sets out to build a customer's engine, he first determines the customer's wants and needs, then matches his engine modi­fications accordingly—right down to the shape of the ports.

“The 600 is neat,” said Yoshima. “It’s much more sensitive to changes than the 900 and you can spin it higher, too.” Yoshima sought to use this project as a testbed for a few theories and possible products, notably an innovative new modular exhaust system design. He tried Keihin 33mm CR smoothbore carbs early in the project, but after months of experi­menting, decided, with their limited needle selection, that the Keihins didn’t fully complement his engine config­uration or the HRC camshafts, so he went back to using the original 34mm CV units with his own pres­surized airbox design. The latter setup makes for a more powerful and ridable powerplant.

One cautionary note: Under extreme, high-rpm race conditions, we found abnormally high wear of the cam sproc­kets, cam-chain tensioner and cam chain. Yoshima cautions to check them every third or fourth race weekend. He also anticipates the new F3’s manual cam-chain tensioner will solve this problem.

As with his CBR900RR racer, Yoshima ran his engine exclusively on Trick Racing Fuel’s 100-octane unleaded because it has shown to burn faster and cleaner than leaded fuel, even those with higher octane levels.

With the exhaust system design, Yoshima went against the recent trend toward the 4-into-2-into-1 config­uration (which theoretically broadens the powerband), feeling that a properly designed 4-into-1 would offer greater power potential. To test his theory, he designed his system with removable midpipes and collectors so that the same headpipes and tailsection could be configured in either layout. At the racetrack, we found that Yoshima’s 4-into-1 configuration (with its uncon­ventional cylinder staggering) produced significantly more top-end power and straightaway speed than the 4-into-2-into-1 without sacrificing too much midrange. Yoshima is contemplating selling a production version of this pipe that would offer both configurations for riders who prefer the broader power delivery of the 4-into-2-into-1 on the street, but could then switch to the 4-into-1 for dragstrip or racetrack duty. With hand-formed, race-quality col­lectors, it wouldn’t be cheap (probably in the area of $1200), but it should offer greater power potential and versatility than any other pipe on the market. Give Ontario a call if you’re interested.

In the end, it’s interesting to note that Yoshima found the CBR600F2 engine more maintenance-intensive than his run-forever CBR900RR engine due to the smaller engine’s higher rpm oper­ating range. He found the 600 engine slightly more expensive as well, figuring he could duplicate this engine for $5500 (not including the ram-air induction) since it would be cheaper to adapt F3 pieces rather than manufacture his own.

The Chassis
The F2's chassis modifications were straightforward with the Fox Racing Shox rear damper and upgraded '94 CBR600F2's cartridge forks revalved by Lindemann Engineering. After much experimentation, we settled on an 800-pound/inch spring on the rear with 12mm more ride height than stock and 1.0kg/mm springs up front with the Ontario triple clamps set 4mm lower than stock. The spring rates are heavier than is conventional for our 165-pound tester, but the heavier rate with lighter preload allows the machine to maintain its cornering clearance in Willow Spring's high-speed corners without sacrificing too much bump compliance. The chassis attitude and ride heights are the best compromise we found between quicker steering and traction: Raise the rear much higher and you'll sacrifice rear-tire traction.

Yoshima also set out to carve as much mass as possible off the chassis by bolting on feather-light AirTech carbon-fiber bodywork, all $2680.45 of it. We promptly destroyed it in a crash the first race weekend. Carbon fiber’s weight savings over more conventional fiberglass comes at a cost; in AirTech’s case, the carbon fiber price is exactly twice that of its fiberglass. After tossing away $2700 in one weekend, we went back to our $830 fiberglass Body by Northstar (which does not include the fuel tank like the carbon-fiber price did), and in 14 months of racing, it hasn’t hit the ground.

As you can see in the accompanying chart, even carbon-fiber bodywork is still significantly less costly than OEM Honda parts; but remember to factor in the price of a paint job and the time and effort required to fit after­market parts. Also, keep in mind that for street-bike usage, it's difficult to beat stock bodywork's durability since most fiberglass parts begin to show spiderweb–type cracks in the finish after more than a year.

One useful bit of knowledge that Yoshima gained is that AirTech’s $1057.85 fuel tank is nearly eight pounds lighter than the $472.73 stock unit, making it the most cost-efficient option in trimming weight from a race bike. Yoshima estimates that he has roughly $3000 worth of titanium and aluminum fasteners (which saved less than four pounds), so the carbon-fiber tank is a comparative bargain (espe­cially considering that it takes weight off the top of the bike, which is very desirable).

What started as a test-fleet beater F2 has been transformed into a full-blooded racer with an enviable win record at Willow Springs. Sit on the 365-pound Ontario Moto-Tech machine with its lowered Chafong bars and higher rearsets, and its street-oriented F2 lineage is all but unrecognizable. Its pumped-up engine screams past 13,000 rpm into the 160-mph range, making it the fastest 600 we’ve ever tested by a significant margin. On the track, its lightning-quick yet stable handling manners, impressive traction and lean angles make it feel more like a four-stroke Formula Two bike than a production-based machine. It also has the stats and numbers to back it up: As of this writing, it’s won more 600 Modified Production and 650 Superbike races at Willow Springs this year than all of the competition combined (nine out of 12 with a pair of seconds and one Did Not Start). Its quickest lap around Willow Springs is a scorching 1:25.92, putting it under the Official Willow Springs 600cc lap record. That’s also quicker than any machine SR has tested with the exception of the awesomely powerful Dutchman Racing YZF1000—not bad for a little 600. Of course, Yoshima’s already bored with it all and starting in on his new CBR600F3. We’ll keep you posted.