 The Kawasaki shuts down based...  The Kawasaki shuts down based on its speedometer signal; recalibrate it with this Yellow Box from Black Robotics and you're on your way to 190 mph-and maybe jail.... |
 Let your Hayabusa be all it...  Let your Hayabusa be all it can be: The Suzuki's ECU shuts down early in sixth gear, but Ivan's TRE-originally intended to bypass softer advance curves in the lower gears-sends fifth gear signals all the time. |
 More evidence: Our original...  More evidence: Our original 1999 Hayabusa boasted a 220-mph speedometer. Our 2001 test unit is pegged at 185. The 2001 ZX-12R speedo is similarly changed from the 2000 model. |
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Yes, they're restricted. Beginning with 2001 models, Japanese manufacturers agreed to limit their motorcycles to top speeds of 186 mph, under the threat of "if-you-don't-we-will" legislation from European governments.
To verify our bikes were in fact restricted, we had our accommodating dyno operator Scott "you guys are killing my bearings" Bartels wind each bike up in sixth gear on his Dynojet dynamometer. At a drum speed of 185 mph, both the Hayabusa and ZX-12R encountered a secondary rev-limiter, well below redline and the usual engine cutout. Disconnect the speedo on the Kawasaki, and hey, it'll spin the drum to 195 or so. Simple, although the fuel injection warning lamp lights up indicating it's not happy with you. The Suzuki, not so easy-disconnect the speedometer and it still cuts out at 185.
While we didn't have a chance to sample a Y2K ZX-12R or Hayabusa, our sister pub Motorcyclist conducted the same tests with its 2000 test units a year ago. Oddly enough, while both bikes ran sub-185 mph in perfect desert conditions, no hint of a limiter was found in the dyno room. We know for a fact that the 2001 ZX has updated cams and a black box, so it's a safe bet that last year's bikes were more subtly restricted to avoid attracting attention.
In any event, some phone calls to those in the know, and we had in our hands a Timing Retard Eliminator (TRE) from Ivan's Rockland County Motorcycle. Turns out the Hayabusa limiter works off gear position and rpm, and Ivan's gizmo informs the ECU it's in fifth gear all the time. Back to the dyno, and the Suzuki spun right to redline in sixth gear. There's an added bonus, too: To protect you from yourself, the 'Busa has different, softer, power curves in the lower gears, and the TRE gives you full steam in every cog-enough of a difference to leave us shaking our heads after our first "derestricted" ride.
Turning our attentions back to the Kawasaki, installing a Yellow Box speedometer recalibrator from Black Robotics neatly fools (er...recalibrates) the speedometer and ECU into thinking you're going slower than you actually are. Set it so the speedo reads 10 percent low, and the poor dyno drum will sing happily to 194 mph.
Off to the real world and our high-desert, topspeed test site, we ran both bikes in stock form. No surprises there, the Kawasaki stuttered past the radar gun at 185.6 mph, while the Suzuki moaned to 183.9 mph. Yawn....Resetting the Zed-Ex's Yellow Box yielded a shrieking 190.2-mph blast (with the speedo reading a leisurely 160 miles per), and the TRE-equipped Hayabusa stormed to 192.4 mph. All with a light tailwind, mind you, but in line with our original 'Busa's 189 mph run two years ago.
Back to Big Dogs: 2001 Suzuki Hayabusa and Kawasaki ZX-12R
This story originally appeared in the October 2001 issue of Sport Rider.