2006 Suzuki GSX-R 600 & 750

By Brian Catterson, Photography by Stephen Piper, Keith Muir

I was thinking it even before Kevin Schwantz put it into words: "Man, wait till you ride the new 750," the 1993 500cc world champion said on the eve of the Suzuki GSX-R600/750 press intro. "It feels exactly like the 600, only faster."

Pause for a brief moment of silence for the late, unlamented 750cc class. Where once the three-quarter-liter category formed the backbone of international Superbike racing (see sidebar, page 58), it has now almost completely vanished, thanks to the marketing arms of the major manufacturers anxious to race on Sunday what they sell on Monday--the exact opposite of the timeworn adage. That's a pity because, in my humble opinion, 750cc is the perfect size for a motorcycle engine.

Apparently, I'm not the only one who feels that way, because whether we realize it or not, the market has been creeping back toward 750s recently; witness the 636cc Kawasaki ZX-6R and Triumph's Daytona 650 and 675. So maybe instead of thinking of the GSX-R750 as being in a class of its own, we should view it as an even larger version of the GSX-R600--a sort of super-middleweight. Because this year more than ever, that's exactly the case.

Flash back to the late '80s, when Suzuki's air-/oil-cooled 600, 750 and 1100cc sportbikes were based on the same engine cases. These were the days before the GSX-R600, when the humble Katana represented Suzuki in Supersport racing (which didn't stop Yoshimura's Doug Polen from winning the '88 AMA title on one). When Suzuki finally produced a proper GSX-R600 in 1992, it was a downsized version of the then-new liquid-cooled 750 ... "and I think it weighed 10 pounds more," joked Suzuki's Motorcycle Planning Group Leader Tak Hayasaki at the '06 intro. Now, the importance of Supersport racing dictates it's the other way around.

It's always entertaining when an engineer from one of the Japanese OEMs gets up in front of a room full of journalists to detail the inner workings of his latest project in English. But we snickered more than usual when hapless Toshikazu Yamaoka explained that the concept of the GSX-R750 was to be the "top performer"--not because as the sole surviving 750 it wins by default, but because his co-worker Norihiro Suzuki had said the exact same thing about the GSX-R600 barely a half-hour earlier! Fortunately, that was the extent of the pair's redundancy as they presented refreshingly concise overviews of their respective models.

The 2006 GSX-R600 and 750 were developed by the same team, which defined four goals: 1. Emotional styling with superb aerodynamics and more functional electrics; 2. Higher engine performance; 3. Smoother deceleration; and 4. Outstanding cornering performance.

Job one was downsizing the engine--and then upsizing it. The engineers started by stacking the transmission shafts to shorten the engine and reducing the pitch between the cylinders to narrow it. That left insufficient room for the 750's larger pistons, so its bore was reduced by 2mm to 70mm and its stroke lengthened by 2.7mm to 48.7mm, taking the bore/stroke ratio from 1:565 to 1:437. That smaller bore in turn reduced the space available for the titanium valves, which was further reduced by the valve stems being tilted more upright to create a shallower, higher-compression combustion chamber. That meant reducing the size of the 750's exhaust valves by 1mm to 23mm. Of course the longer stroke would have made the 750 shake, so the engineers added a balance shaft like on the 1000. Topping it all off is a new fuel-injection system with twin injectors, the throttle bodies measuring 40mm on the 600 and 42mm on the 750. Although Suzuki doesn't publish power figures, the engineers reported that the '06 600 produces 5 more horsepower than last year's model and the '06 750 2 more, which should equate to approximately 110 and 130 bhp at the rear wheel, respectively.

Reducing the physical size of the engine opened up a world of possibilities for the chassis, and the engineers capitalized on every one. They made the frame narrower so it wouldn't feel as wide between the rider's legs. They made the gas tank narrower and shorter, which let the rider scootch farther forward. And they made the seat lower, which let the rider tuck in tighter while giving shorter riders firmer footing. Last but not least, they gave both bikes a new exhaust system, with the large, heavy muffler positioned under the engine in the interest of mass centralization. Maybe Erik Buell had it right after all?

By Brian Catterson
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