SR Archive: Horsepower Unlimited Kawasaki GPz880 Turbo - UFO 1996

Don’t judge a UFO by its bodywork

This article was originally published in the October 1996 issue of Sport Rider.

It took 9.34 seconds to convince us that Horse­power Unlimited's 12-year-old Kawasaki be­longed at UFO '96. Mike Chestnut, the man behind HP Unlimited, promised Sport Rider that the GPz wouldn't disappoint. "It looks stock," Chestnut admitted, "but we're getting 230 horsepower reliably."

Horsepower Unlimited Kawasaki GPz880 Turbo
Horsepower Unlimited Kawasaki GPz880 TurboSport Rider

Inside the UFO Turbo, which belongs to customer John Voter, beats Chestnut’s first 880cc piston kit. Combined with his beautiful air-to-air intercooler and substantially re­vised fuel injec­tion and turbo­charger, the 880 kit reduced turbo lag to almost inconse­quen­tial pro­por­tions. This in turn gave us the kind of power to yank the front wheel off the ground in third or fourth gear with just a touch of the horn button, which activated the second stage of the dual-stage wastegate. Typical comments after the street ride were, “Wow, what a great street bike…and it hauls ass!”

Voter opted for a set of 17-inch Hypertek wheels that look great painted red and allow the ’84 machine to wear modern, 17-inch tires, in this case Dunlop Sportmax radials. The stock suspension was rebuilt and Richard Sims machined the hangers for the Performance Machine six-piston calipers (with 11-inch PM floating rotors), and the upgraded chassis made exploiting the horsepower that much more enjoyable.

Horsepower Unlimited Kawasaki GPz880 Turbo
A cool intake charge makes more horsepower, so HP Unlimited designed and built this air-to-air intercooler. The turbo’s K&N air filter has been removed for photos.Sport Rider

The minor upgrades to HP Unlimited’s GPz chassis weren’t enough to put it on par around the HPCC test track—no surprise there. The main reason we enjoyed the bike on the track was due to the killer PM brakes that easily dented the bike’s incredible acceleration. Knock the pace down a few notches, as you would on the street, and the Kawi was the surprise of the group, and certainly the only true street bike present, running with a full comple­ment of turn signals, mirrors, centerstand, complete muffler and even stock body­work, as Chestnut proudly pointed out.

While other teams were busy length­ening their adjustable swingarms, Chestnut just gave us instructions on launching his stock-wheelbase GPz: “Try to wheelie a bit less off the line, go to second manually, then just before the shift to third, hit the horn button (which triggers not just the wastegate’s second stage, but the Holeshot Performance electric shifter), then leave it pinned for the next two shifts.” When we got it right, the payoff was the third-quickest time in UFO ’96 (9.34 seconds at 156.2 mph)—and one that would have won UFO ’95! Then we went to top speed and the impressive 1984 GPz750 Turbo came into its own.

Horsepower Unlimited Kawasaki GPz880 Turbo
The 17-inch Hypertek front wheel is practically hidden behind the Performance Machine floating rotors and six-piston PM billet calipers. The upgraded brakes give testers confidence to explore the bike’s vast horsepower reserve.Sport Rider

We finally found the right chassis com­bination by dropping almost all the spring out of the back, re­moving the front fen­der and trashing the steering damper to eliminate a nasty wobble. Bang! 192.719 mph at 11,600 rpm. Chestnut smiled and said, “See if it will run to 12,000, because I don’t have any taller gearing.” The final run ended with a blown head gasket, courtesy of a bit too much horn pushing, and the phenomenal GPz coasted to a stop with a 200-plus mph run inside it with a simple change of sprockets. Chestnut considered UFO ’96 a three-day marathon test for his new 880 kit, and we learned that you can’t judge a UFO by its bodywork.

Horsepower Unlimited Kawasaki GPz880 Turbo
This bullet, owned by John Voter, ran a 9.34 in the quarter-mile using the stock wheelbase, with the front end lowered slightly using a tie-down strap to help reduce wheelies off the line.Sport Rider


  • Horsepower Unlimited 880cc piston kit; copper head gasket; drop-in turbo cams; heavy-duty clutch springs; lock-up clutch; Stage 4 turbo upgrade; dial-a-boost kit; electronic two-stage wastegate; bored stock throttle bodies; upgraded fuel injectors; modified fuel-injection computer; ported collector pipe; custom exhaust; intercooler kit; oxygen sensor kit; compressor bypass valve; modified oil pan, high-performance ignition; mechanical cam-chain tensioner; slotted cam sprockets
  • APE cylinder nuts; heavy-duty valve springs
  • K&N air filter
  • Holeshot Performance electric shifter
  • RPM ported cylinder head
  • RB Racing intercooler technical assistance
  • Turbonetics turbo technical assistance


  • Frame straightened by The Frameman
  • Hypertek wheels
  • Dunlop Sportmax radials
  • Telefix fork brace; steering damper
  • Horsepower Unlimited rear fender kit; headlight cover; liquid-filled boost gauge
  • Sims Engineering brake-mount kit; wheel fitment
  • Lindemann Engineering rebuilt fork

  • Replacement Cost: $12,000

Temp Gauge
High Low
200 mph potential out of a 12-year-old design The gearing during top speed
Reliable and rocket-fast Chassis performance can’t match the motor
Dual-stage boost trigger made for endless entertainment
Horsepower Unlimited Kawasaki GPz880 Turbo
Test Track Lap Time 1:58.01
Quarter-mile Time (sec) 9.34
Quarter-mile Speed (mph) 156.2
Dry Weight 482 lbs

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