The Kawasaki GPz1100 deserves much recognition and appreciation, writes Ian Falloon…
When Kawasaki embarked on building motorcycles in the early 1960s it was the two-stroke range that established their performance image. A string of class-leading performance bikes emerged from Akashi; notably the rotary-valve Samurai, and three-cylinder 500cc H1 and 750cc H2.
Even when the four-stroke Z1 replaced the H2 it still maintained Kawasaki’s performance reputation. But during the late 1970s through until 1980 this image stagnated as Kawasaki concentrated on producing LTDs and customs.
It wasn’t until the release of the GPz series for 1981 that Kawasaki diehards were reassured that it was business back to normal. Strikingly styled, with performance to substantiate their image, the GPz’ impact was so strong that it put Kawasaki firmly back at the top of the performance class.
The first GPz Kawasaki was the GPz1100B of 1981. The 1098cc four-cylinder engine was still based on the original Z1, but electronic fuel injection saw the power increase to 108 horsepower at 8,500 rpm. However, the twin shock GPz1100 was still fundamentally an old school 1970s Japanese Superbike.
In a straight line there was little to touch it, but it was no agile sports bike. Once you started manhandling this wide, large beast through a series of fast corners the chassis deficiencies began to manifest itself. To overcome handling woes other Japanese companies were experimenting with a single shock rising rate rear suspension set-up and now it was Kawasaki’s turn.
This was to be the final Z1-based high performance GPz-series machine before the release of the new liquid-cooled 16-valve generation and following the example of the Uni-Trak GPz550, the 1100 also gained Uni-Trak for 1983… Although it may have been about to be superseded, Kawasaki still went to a lot of effort to keep the performance competitive and the GPz1100 managed to retain the big-bore performance crown for yet another year.
Developments to the venerable air-cooled 72.5x66mm four included 38mm inlet valves and hand-finished cylinder heads. Along with stiffer valve springs the valve adjustment mechanism moved to the top of the valve stem as on the Z650/750.
The compression ratio went up to 9.5:1, and an electronic spark advance system replaced the earlier mechanical unit. With a totally revised DFI (digital fuel injection) the GPz1100 was the most powerful Z1-based Kawasaki ever, producing an impressive 120 horsepower at 8,750 rpm. These ponies were not imaginary either.
Testing a GPz1100 in February 1983, Cycle magazine found it to be the first production motorcycle to break the ten second quarter mile barrier with a time of 10.91 seconds at 124.65 mph (200 km/h).
The chassis also came in for total revision, with a box-section aluminium swingarm (with eccentric adjusters) operating a Uni-Trak rear suspension system. The down side of the Uni-Trak was an increase in wheelbase, to 1,565mm, resulting in relatively slow and stable steering. New 37mm Kayaba forks provided a three-position hydraulic anti-dive system and completing the chassis revisions were wider three-spoke 18 and 17 inch alloy wheels.
With its unique tank-mounted LCD instrument panel and frame-mounted half fairing the styling of the GPz1100 was decidedly muscular. But even if it did deliver the promised performance this was still a large and heavy motorcycle.
The substantial 246 kg dry weight may have deterred enthusiastic scratching and the small 246 mm discs on the front were barely up to the task, but few motorcycles could equal the GPz’s all round competence in 1983.
Although released amidst a fanfare of publicity the GPz’s reign at the top of Kawasaki’s line-up was short lived. Only a year later the GPz900R appeared, effectively rendering the GPz1100 a dinosaur. But that is doing the GPz1100 a disservice.
It may have been a relic of the past but the GPz1100 represented the end of the line of Kawasaki’s Z1-based air-cooled Superbikes. And while the early Z1 is now a highly prized collectable, the final GPz1100 remains forgotten and overlooked. As a one year only model, and representing the end of the line, the 1983 Kawasaki GPz1100 deserves much more appreciation and recognition.
Australia’s go-to-guy for classic motorcycle wisdom. Ian has written nearly 45 books on motorcycles that each offer unparalleled insight on the historical and technical development of particular makes and models.