Retrospective: 1984-1985 Kawasaki ZX750-E Turbo

1984 Kawasaki ZX750-E Turbo
1984 Kawasaki ZX750-E Turbo.

“If intent is enough to convict, anyone purchasing Kawasaki’s 750 Turbo should have his driver’s license revoked,” wrote one moto-journalist in 1984.

This Kawasaki was the last of the corporate turbos, which began with Honda’s CX500T in 1982, moved along in 1983 to Suzuki’s XN65 and Yamaha’s Seca Turbo, and ended here. Though Kawi bean counters probably wondered why anyone bothered doing the project, as the other OEMs had dropped their turbos for the 1984 model year. But the money had been spent, so might as well put it out on the market.

The major question was: Why build a turbocharged motorcycle? It was a complicated and expensive endeavor, and more horsepower could always be added by using a bigger engine…but turbo-mania was in the air. That could be blamed on Kawasaki, which had sold a KZ1000 with an aftermarket turbo kit back in 1978 and ’79 (Retrospective, April 2014) with moderate success. Then the factory boys began fiddling with a KZ650 in 1980, a good bike that had been around since 1976 and was admittedly getting a bit long in the tooth. R&D decided to update the 650, an in-line four with DOHC and two valves per cylinder, by boring out the 652cc engine another 4mm, now 738cc with a 66mm bore and 54mm stroke. And this GPz750 was the model the turbo engineers decided to build on.

1984 Kawasaki ZX750-E TurboThe ZX750 Turbo was actually introduced in April of 1983, at an Austrian racetrack. Kawasaki sensibly felt that this bike, with its potential and being ridden by throttle-happy journalists, really needed a closed course rather than public roads. That could happen later when magazines received their test bikes.

First we might briefly examine the turbocharging principal. The basic idea is that the quicker fuel can be crammed into the combustion chambers, the more powerful the engine will be. There are two ways of doing this. The first uses a contraption called a supercharger, a mechanism that literally blows the fuel into the engine…as on Kawasaki’s current Ninja H2 models. The main disadvantages of the supercharger are its expense, and the fact that a drive-mechanism has to be routed from the engine. The turbocharger, on the other hand, is powered by the exhaust gases, and merely requires rerouting the headers into a turbine, which then forces the fuel-air mixture to move along very swiftly.

1984 Kawasaki ZX750-E TurboKawasaki had taken a good account of the previous turbo efforts, with the biggest complaint always being “turbo-lag”—the time difference between twisting the throttle and the turbo kicking in. To diminish this, the engineers put the turbine as close to the exhaust ports as possible, with the four short header pipes going down to the turbine mounted at the front of the crankcase.

Air intake was another matter, and Kawasaki chose to put the oil-foam filter down low by the countershaft sprocket, allowing for quick access to the turbine, though it was not good on dirt roads. But who would want to ride a turbo on a dirt road? The air rushed into the 47mm compressor, made by Hitachi and capable of spinning at some 200,000 rpm, then sped along to the plenum chamber. The what? The official name for an airbox. Where the boost was pressurized to 11.2 psi as it flowed through the Digital Fuel Injection system.

The Kawi engineers did not like the idea of the engine exploding, as was popular with the previous turbo kit model, so cutouts were engineered if the boost pressure exceeded its prescribed limits, or if the engine revved to more than 11,500 rpm. After all, this Turbo was under warranty, which the earlier unofficial one had not been. However, talented mechanics could figure out how to get more power—which may be one reason why only some 10 percent of the 3,500 Turbos sold in the U.S. still exist.

1984 Kawasaki ZX750-E TurboEngine alterations were few, with less aggressive camshafts, compression ratio lowered to 7.8:1 vs. the GPz’s 9.5:1, and new pistons better designed to cope with the extreme heat that the turbo could create. Rear-wheel power went from a little less than 70 ponies for the GPz to 95 mustangs for the Turbo. Torque went from 41 lb-ft to 63 lb-ft. Kawasaki ads claimed horsepower was 112, but that was probably taken at the crankshaft.

Leaving the crankshaft, the Turbo power went along a strengthened primary chain and a stronger clutch. The output shaft in the gearbox was made heftier, and four out of the five gear ratios were altered to make them taller. Minor alterations came to the full-cradle chassis, with a single-sided swingarm called Uni-Trak mounting a single shock with air adjustability and rebound damping alterations. Up front the 37mm fork tubes also had adjustable air pressure and an adjustable anti-dive system, which testers seemed to like. Rake was 28 degrees, trail, 4.6 inches; this was set up more for the straight line than the curves, but handled quite well wherever it was taken.

1984 Kawasaki ZX750-E TurboThree-spoke cast wheels had a 110/90 tire on the front, 130/80 at the back, with the brakes straight off the GPz1100—dual discs and single-piston calipers on the front, a single disc at the back. Distance between the axle centers was 58.7 inches, and wet weight, with five gallons of gas in the tank, was some 555 pounds.

Get on the saddle, turn the key, push the button and a normal-sounding engine comes to life. Roll along to your favorite country road, hit the throttle at 3,500 rpm and a bit of a lag was evident. However, from 6,000 rpm the boost was smooth…and arm-wrenchingly apparent.

Then Kawasaki introduced the Ninja 900, with liquid cooling, four valves per cylinder, slightly more power…and less expensive. Sayonara, Turbo.

LEAVE A REPLY

Please enter your comment!
Please enter your name here