Cycle News - Archive Issues - 1980's

- ~ 00 First ilDRression: 1984 Kawasaki GPz900R Enterthe Ninja By David Dewhurst Photos by Tom Riles and Dewhurst Kawasaki engineers don't hide the fact that they like performance. You need look no further back than to America's original muscle bike, the 900cc Z-l, their 500cc two:- 16 troke triple or the latest brightred GPzI 100 for proof of that. So, when those same engineer unveiled the all-new GPz900R there was no real doubl about the bike's intended role. Kawasaki described Ihe fully faired 900as, " ... having the performance of an 1100 and the agility of a 750." Plenty of motorcycle companies, including Kawa aki, have tried to make that same claim for their turbos. This time around though the folks at Kawasaki really seemed to believe it was true. "It's as fast as the Turbo and the 1100," said one excited designer. "It's the besthandling Kawasaki we've made," said another. They weren't joking. Two days of racing around Laguna Seca were enough to convince journalists from around the world that Kawasaki has created one of the fastest street-legal motorcycles that ever turned a wheel. That wasn't much of a surprise considering Kawasaki's performance reputation. But what was surprising was the apparently conventional engineering that produced this two-wheeled rocket, Had this been any other Japanese manufacturer the GPz900R might have been powered by a V-4 motor and housed in a square-section tube frame. It might also have been controlled by a computerized brain and monitored by digital instruments. It isn't, Instead it's powered by a motor with a time-honored in-line-fourconfiguration and doesn't have anything much more exotic than a new design of Keihin carburetor. Don'l let lhis apparent simplicity fool you though, Whalthe GPz900R lacks in hi-tech hardware il more than makes up for in down-to-earth performance. Everything about the all-new liquid-cooled in-line four seems to have been crafted for speed. From its 16-inch front wheel tQ its concentric rear-axle adjusters, the latest GPz is a down-sized rocket waiting to be launched. When you ignite this red and gray beauty a familiar in-Iine-four-cylinder motor roars into life. But that is where any similarities between this and any previous Kawasaki motor ends, The new GPz is the first in-line four to use liquid cooling around its iron liners, With this more efficient dissipation of heat, Kawasaki was able to move the wet liners closer together lhan the previous air-cooler without fear of heat distortion. And wi th no need for extra air-cooling space between the normally hot-run: ning center cylinders, KawasakI moved the cam-chain tunnel to the left side of the motor where it could be more easily maintained. The overall engine width was further reduced by moving the alternator from its regular location on the end of the crank to a position above the gearbox, just behind the cylinders. This slimming program has made the GPz900R an amazing 4.86 inches narrowerrhan the original Z-I which allows the bike to achieve much greater lean angles before metal starts scraping the road, But Kawasaki engineers knew that lean angles alone weren't enough to make the G Pz900R a rocket to be reckoned with. That's why they reworked the entire combustion area of the motor to squeeze out enough power to bury mostllOOs, Inside each 72.5mm bore are four large valves with a narrow induded angle (inlet 18.5 degrees, exhaust 16.4 degrees). Kawasaki claims this valve layout, combined with an II: I compression ratio and a relatively long valve-open duration gives greater breathing e£ficiency than any previous Kawasaki street motor. And you don't need to look at a horsepower graph to check thatdaim. Any pieceof straight asphalt will confirm that with a claimed 112 horsepower at 9800 rpm, the GPz900R is a very fast motorcycle. You won't notice a sudden rush of power at any point in the powerband. Unlike the peakier Yamaha FJ 1100, the Kawasaki just punches out a continuous, smooth rush of horsepower that is very easy to use. Around Laguna Seca 's sweeping high-speed turns the 900 would, jusl as the excited engineers had predicted, easily stay with, and sometimes outhaul. both the 1100 and Turbo. And unlike both its peakier stablemates, the new 900R could be pushed harder on the exit of turns without fear of a udden rush of power breaking the rear wheel loose. And in the less-predictable world of canyon racing that should prove to be a real advantage. Kawasaki designers claim that the new Keihin carbs are partly responsible for this predictable power delivery. Described as a semi-flat slide design, the carbs have tiny slides that are too small to completely obstruct each carb's 34mm venturi. To take up the remaining space between slide and carb body, Keihin used flat ex tensions on either side of the slide at right angles to the direction of airflow. This unique design is claimed to improve throllie response and provide more efficient fuel £low at high speed. One designer also noted that carbs are considerably cheaper to manufacture than elaborate fuel injection systems pioneered by Kawasaki on theGPzI 100. In an age of evermore elaborate designs, Kawasaki's cost-conscious approach is commendable, Better yet, the new carbs seem to

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