Source: Bike Bound
In 1981, Kawasaki introduced the GPz1100, which would be the ultimate evolution of the mighty air-cooled Zed fours born from the legend itself, the Z1. Before long, the sport-riding world would be dominated by liquid-cooled, alloy-framed Ninjas and Gixxers, but for a blood-red moment in motorcycling history, the GPz was the king of the breed:
“Kawasaki’s meanest Zeds haven’t always been green – the GPz1100 was slathered in bodywork painted red by the blood of its inferior rivals.” –MCN
The GPz1100 was inspired by Kawasaki’s AMA superbike racers, featuring a 1089cc engine that made 109 bhp at 8500 rpm — the most powerful production four at the time. It was fuel-injected, and boasted higher compression pistons, a lightened roller-bearing crankshaft, and higher lift / shorter duration cams as compared to its predecessor, the Z1000H. Later versions would boast 120 bhp.
John Nutting of Classic Bike Hub recalls hitting an indicated 158 mph — a true 152 mph — at the UK’s famed Motor Industry Research Association (MIRA) track before he had to slam the brakes on the mile-long straight:
“OK, it wasn’t a properly timed speed, but as far as I was concerned the GPZ1100A1 was the first road bike I’d tested at more than 150mph at MIRA.”
Though GPz1100 was expensive, the fuel injection finicky, and handled like a boat beneath the sporting speeds, it was all part of the mystique:
“This only accentuated the image of what was a blisteringly potent machine which would be the final blast in a series of air-cooled four-cylinder Kawasakis that had made the factory the performance king since the Z1’s launch in 1972.” —Classic Bike Hub
Recently, we heard from the good folks at Atlanta Motorcycle Works, who just finished bringing this ’81 GPz1100 back to life — with some choice modern upgrades. Highlights include an engine rebuild with Mega Cycle cams, oversized valves, and 1136cc pistons, as well as a switch from the outdated fuel injection to Mikuni RS34 Flatslide carbs.
“After we tuned the engine on our in-house dyno the bike produces an impressive 115hp at the rear tire compared to 90hp stock.”
There’s also a new ceramic-coated exhaust, oil cooler, YSS rear shock, GSX-R front end, ZRX swingarm, Michelin Pilot Power 2CT rubber, repainted bodywork, and more.
Below, Jeff from Atlanta Motorcycle Works gives us the full story on this resto-modded monster.
Kawasaki GPz1100 Restomod: In the Builder’s Words…
We have enjoyed bringing another classic motorcycle back to life and improving it along the way. This 1981 Kawasaki GPZ1100 came to us in need of some help with both the mechanicals and cosmetics.
Before…
We completed an engine rebuild including Mega Cycle cams, oversized valves and pistons to now be 1136cc. To help this monster breathe we overhauled the Mikuni RS34 Flatslides and installed a competition baffle in the ceramic-coated Kerker exhaust. To help keep the engine cool we installed a Grumpy’s Oil Cooler. After we tuned the engine on our in-house dyno the bike produces an impressive 115hp at the rear tire compared to 90hp stock.
To help get all that power to the ground, and help the bike handle and stop, we addressed the suspension next. We installed a custom-length YSS rear shock to address a ride height issue from the previously installed GSX-R front end and ZRX swingarm. At the same time, we replaced the failing fork seals. We also rebuilt the brake master cylinder and calipers and replaced the brake lines and brake pads to provide maximum stopping power. We also installed a set of Michelin Pilot Power 2CTs to achieve maximum grip.
Once all the mechanicals were sorted out we turned to the cosmetics. We repaired and lined the rusted fuel tank. The customer requested a front fairing be installed to match the later GPZs, so we had to fabricate a custom bracket to meet our standards and house the customer’s aftermarket digital gauge package. We replaced the original turn signals with custom sequential LED units that better fit the lines of the bike. Once all the fabrication was completed we had the bodywork painted and striped in the factory colors.
Both the customer and we are very pleased with the final product which stays true to the original bike while also having modern performance and reliability.
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