Motorcycle Classics

Dream Machine: 1981-1984 Kawasaki GPz1100

Kawasaki GPz1100
Years produced: 1981-1984
Power: 104hp @ 8,500rpm (1983-on)
Top speed: 135mph (period test)
Engine: 1,089cc air-cooled DOHC 8-valve inline four
Transmission: 5-speed, chain final drive
Weight/MPG: 551lb (w/half tank fuel)/38-52mpg
Price then/now: $4,399 (1981)/$2,500-$6,000

The early-mid-1980s were a period of unprecedented domination of the U.S. motorcycle market by Japanese makers. Britain’s motorcycle industry was dead; in Italy, Laverda was dying and Ducati struggled on, seemingly destined for the same fate until rescued by Cagiva in 1985; and Harley was just emerging from its disastrous AMF tenure. BMW offered a viable alternative — but at a premium price.

This was the era of the “UJM” — the Universal Japanese Motorcycle — a naked bike with an across-the-frame, air-cooled, 4-cylinder, double overhead cam engine of around 1 liter, mounted in a chassis that never quite seemed up to the engine’s performance potential. These motorcycles were capable of speeds in excess of 130mph, which, just a decade before, would have been racing territory. And they brought with them reliability, quality finish and durability.

In 1981, and facing serious competition from Suzuki’s GS1100E, Kawasaki engineers decided that one more stretch of the Z900-based KZ1000 engine would hold the fort until the all-new liquid-cooled GPZ1000RX replaced it in 1985. To gain the extra capacity, bore was increased by 2.5mm, giving 1,089cc versus the KZ1000’s 1,015cc. Bigger valves, revised cam timing, a compression boost to 8.9:1 and Bosch-derived Nissan fuel injection increased power to a claimed 105 horsepower (90 rear-wheel horsepower in Cycle’s test). Taller pistons with shorter rods spun a new, lighter crank, and drive to the two overhead camshafts was now by Hy-Vo chain with slipper tensioners. The transmission was the same as the 1000 — straight-cut gears to a 5-speed gearbox — but the kickstarter was eliminated.

The KZ1000-based frame was strengthened and lengthened by around 2 inches, while the rake increased from 28mm to 29mm, giving a long-ish 60.6mm wheelbase. Two rubber engine mountings held the front of the engine, with a single solid mount at the rear. The front fork had factory-preset damping only (although air-adjustable for preload), while the rear shocks had five damping settings. Cast alloy wheels (19-inch front, 18-inch rear) were fitted with 10.2-inch triple-disc brakes. And it was the brakes that caused Cycle World’s testers some concern.

“At low speeds (under heavy braking) the front tire would slew from side to side just before breaking loose… At higher speeds the front end of the motorcycle would jackhammer, bouncing the front wheel off the ground, which caused the tire to lock… Stopping distances increased markedly in successive stops as the brakes got hotter, grabbier and harder to control,” CW’s testers said.

Why the braking issues? CW noted that the Kawi’s 3.25-inch front tire was narrower than the GS1100 (presumably for lighter steering), while the GPz750-derived brakes were overly aggressive: “With only two fingers on the lever, the front tire can be locked at any speed,” they noted. This was unfortunate, because the big Kawi went well, with standing quarters in just over 11 seconds at 119mph, fastest in its class at the time. And it handled surprisingly well for such a large, heavy (550 pounds curb) motorcycle — although long-range comfort was perhaps lacking.

Getting beyond the brakes, the GPz was highly regarded. “No bike has better throttle response,” CW said. “As the pace picks up on twisty canyon roads, the GPz1100 has a steering quickness and precision… It is exceptionally stable.” But also added, “The seat is firm, not plush… suspension can’t be bothered with absorbing every little bump.”

The GPz1100 got a major makeover in 1983, with more power (104 rear-wheel horsepower), Uni-Trak monoshock rear suspension and, perhaps critically, a change of rubber to 110/90 x 18-inch front and 130/90 x 17-inch rear. Cycle took the revised GPz1100 to the strip and restored its crown as the fastest 1100 in a straight line, with a standing quarter that broke into the 10s (though the 1983 Suzuki GS1100ES soon equaled that).

Summing up the 1981 version, Cycle World wrote: “What we have here isn’t just another fast bike. What we have here is the answer to the sports rider’s dream.” Maybe so. But in a three-way shootout in 1983, Cycle concluded that the best all-around 1100 was still… the Suzuki GS1100ES. MC

Contenders: Alternatives to Kawasaki’s big-bore GPz1100

1982-1983 Suzuki GS1100E
Years Produced: 1982-1983
Power: 108hp @ 8,500rpm (claimed)/140mph (period test)
Engine: 1,074cc air-cooled DOHC 16-valve inline four
Transmission: 5-speed, chain final drive
Weight/MPG: 562lb (wet)/40-50mpg
Price then/now: $3,999 (1982)/$2,500-$4,500

Suzuki was last of Japan’s Big Four into the 4-stroke game, but its 4-cylinder GS bikes quickly became the benchmarks in their class. The GS1100E introduced Cosworth-style 4-valve cylinder heads, known as TSCC, or Twin Swirl Combustion Chamber in Suzuki-speak, with simple screw-and-locknut valve adjustment. Fueling was by four 34mm Mikuni carburetors, with sparks provided by transistor ignition. Below, the familiar bulletproof roller-bearing crankshaft drove the 5-speed transmission by helical gear with chain final drive.

The sturdy steel tube frame used a box-section alloy swingarm for extra rigidity. Up front, an air-assist Showa fork with “anti-div” used hydraulic pressure from the front brake. The triple-disc brakes used floating calipers. Overall, testers liked the 1100: “This GS is the most comfortable, best handling big street bike money can buy,” said Cycle in 1982. The GS1100E was good enough to be named Cycle World’s Superbike of the Year for three consecutive years from 1981-1983, and its combination of sub-11-second quarter-mile times, nimble yet stable handling, long-distance touring comfort, simple maintenance and bulletproof reliability contributed to the GS1100E’s position as fifth “most significant motorcycle” from the previous 35 years by Rider magazine in 1999.

1983 Honda CB1100F
Years Produced: 1983
Power: 108hp @ 8,500rpm (claimed)/144mph (period test)
Engine: 1,062cc air-cooled DOHC 16-valve inline four
Transmission: 5-speed, chain final drive
Weight/MPG: 580lb (wet)/35-45mpg
Price then/now: $3,698/$3,500-$6,000

The CB1100F was a stop-gap model sold for one year only while Honda completed development of its liquid-cooled V4s. Essentially a bored-out CB900F (from 64.5mm to 70mm), the 1100F featured a 4-valve double overhead cam engine with a 5-speed transmission, 33mm Keihin “pumper” carbs and magnetically triggered electronic ignition.

With technology from the Euro-market CB1100R, the 4-valve engine produced a claimed 108 horsepower at the crank, and was packaged in a conventional steel tube frame with a bikini fairing, TRAC anti-dive fork, cast alloy tubeless-tire wheels and adjustable handlebars. Wheels were 1 inch smaller than the 900, using 18-inch front and 17-inch rear, reducing the seat height by a half inch.

The CB1100F offered similar performance to the GS1100 and GPz1100 (top speed was better than the GS, although the GS would beat it in the all-important quarter mile), but it was also less expensive at $3,698 against $4,499 for the GPz and $4,350 for the GS1100ES in 1983. Said Cycle Guide magazine, “You might be tempted to call the CB1100F the performance value of the year… a brilliantly conceived and executed motorcycle, capable of outperforming most of the riders lucky enough to swing a leg over one.

  • Published on Feb 13, 2018
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