Kawasaki ZX 750
Turbocharged Kwacker from 1983
'The ZX750 Turbo was a very different proposition. Like the modern Ninja H2s, the ZX was an official model from Kawasaki, whose factory engineers said the reason for a delay in building it was that they had been determined to perfect the design. By the time the
ZX was ready for launch in 1983, Kawasaki had become the last of the Japanese manufacturers to release a turbocharged production bike'
THE ZX750 TURBO EMPHASIZED its speed almost immediately on its launch at the fearsomely fast Salzburgring circuit in 1983 — but not in quite the way Kawasaki had intended. Accelerating out of the long, final righthand bend towards the end of the second lap of my first session astride the new turbo-bike, I was surprised to see a rider sitting on a stationary ZX in the following bend’s gravel trap, having failed to slow in time for the tight final chicane.
The red-and-black Kawasaki that I was riding picked up speed so rapidly out of the right-hander that I had to brake hard to make the bend myself. But I’d forgotten the incident by the time I reached the same turn on the second lap of my next session — only to find a different rider in the same place in the gravel, having gone straight on in identical fashion!
It was obvious what had happened: both riders had been caught out by the torrent of horsepower that was unleashed when the Kawasaki’s turbocharged engine came on song. Like the firm’s latest Ninja H2 SX, the ZX used its forced induction to deliver a mighty surge of straight-line stomp that required its rider to be fully awake at all times.
Those ZX launch incidents, during which both riders thankfully stayed on board, confirmed what I and the other journalists were also discovering on Salzburg’s long, Armcolined straights. This powerful and smooth-running new turbocharged model very much lived up to the reputation that Kawasaki’s air-cooled, two-valves-per-cylinder fours
had enjoyed since the mighty original 903-cc Z1 had been released 10 years earlier.
That reputation had slipped slightly in the late 1970s and had already been revived to a degree by a turbocharged model, at least in the USA. In 1978, with Kawasaki’s Z1000 four being challenged by more powerful rivals, including Honda’s CBX1000 six and Suzuki’s GS1000 four, the firm’s US importer had produced a special model by bolting a Ray-jay turbo (complete with Bendix carburettor and collector exhaust) on to the Z1-R, the angular, bikini-faired version of the Z1000 that Kawasaki had released that year.
This unofficial model was known as the Z1-R TC Turbo and was available only in the States. Its turbo boosted the 1,015-cc motor’s standard output of 90 PS to about 125 PS, gave very rough low-rev running, and resulted in a very quick standing quarter-mile time of less than 11 seconds. That had made the Z1-R TC popular enough for 1,600 units to be sold in the States in 1978 and ’79, even though it came with no engine warranty.
The ZX750 Turbo was a very different proposition. Like the modern Ninja H2s, the ZX was an official model from Kawasaki, whose factory engineers said the reason for a delay in building it was that they had been determined to perfect the design. By the time the ZX was ready for launch in 1983, Kawasaki had become the last of the Japanese manufacturers to release a turbocharged production bike, following Honda’s CX500 (and later CX650) Turbo, Yamaha’s XJ650 Turbo, and Suzuki’s XN85.
If the Kawasaki was the last of the Big Four’s blown bruisers, in many respects it was also the best. When it reached the market in 1984, two years later than many people expected, the ZX wasn’t merely the world’s fastest 750. It was as quick as just about anything on two wheels — very close in straight-line performance to Kawasaki’s own conventionally aspirated flagship, the GPz1100.
The Turbo’s peak output of 112 PS at 9,000 rpm was 8 PS down on the GPz1100’s figure, according to Kawasaki, but the turbocharged motor was stronger below 7,000 rpm. Equally importantly, the Turbo — whose official name was the ZX750 Turbo although the initials on its engine covers meant it was often called the GPz750 Turbo — performed with an addictively smooth and rev-happy feel that made it great fun to ride.
Kawasaki’s Turbo also suffered far less than the rival firms’ offerings from the traditional drawback of turbo lag (the delay between opening the throttle and the engine responding) caused by the way a turbocharger relies on exhaust gas to spin it, so that it can force extra intake mixture into the engine. Part of the reason for that was Kawasaki’s positioning of the turbocharger in front of the 738-cc motor. The XJ650 Turbo and XN85 held their turbos to the rear of their straightfour engines, a long way from the exhaust ports.
Positioning the turbo up front meant the ZX reacted more quickly, but created a problem of exhaust downpipe routing which Kawasaki overcame by using heat-resistant steel pipes to the Hitachi turbo unit. The system was still complicated. The air-filter sat in an unusual position on the left of the engine, outboard of the drive sprocket. Air passed from there down and round to the compressor, then upwards
back round the left side of the engine for a high-pressure swirl in the air-box before it reached the bank of GPz1100-style fuel-injectors.
The air-cooled, eight-valve motor itself was conventional Kawasaki. Essentially a detuned and strengthened GPz750 lump, it used a Z650 cylinder-head to reduce compression ratio from 9.5 to 7.8:1. Pistons were flat-topped and heavy-duty, camshafts gave less lift and duration, bottom-end parts were beefed up, and oil pump capacity was increased.
One drawback of putting the turbo unit up front was its vulnerability to damage in a crash. Kawasaki countered this by building an aluminium brace into the ZX750’s full-length fairing: the silver strip in front of the engine was part of the frame and added rigidity as well as protection.
Much of the chassis was from the GPz750, with the exceptions of a longer steering head and a stronger box-section aluminium swingarm. Forks were 37-mm air-adjustable units, complete with hydraulic antidive; rear shock was a typical Uni-Trak unit with air assistance and four damping positions. Dry weight was 233 kg, which sounds a lot now but was respectable at the time; roughly midway between the standard 750’s 219 kg and the 1100’s 244 kg.
It all worked well, because the Turbo impressed almost everyone who rode it — starting with me and other journalists on that launch at the spectacularly hilly but dangerous Salzburgring. I recall being mightily impressed that the new bike recorded just over 225 km/h on the back straight, exactly the speed indicated by the conventionally aspirated GPz1100s that Kawasaki had rather bravely brought along for comparison.
I also remember being impressed by how little it suffered from turbolag, especially on the track where it was possible to keep the revs up and plenty of boost showing on the gauge. And I recall the big bike handling and braking very well, and staying stable even through the scarily fast left-hand bend towards the end of the lap.
I can also report that a good Turbo is still a very enjoyable bike to ride many years later, as my blast on this well-preserved example confirmed. This Kawasaki had covered just over 50,000 km, but it felt as strong as it would have done when new. Every time the ZX had a clear stretch of road ahead of it, a tweak of the throttle sent it rocketing forward with a smooth, relentless force that felt as addictively good as it did back then.
Provided the tacho needle was somewhere in the middle of its range and there were some bars showing on the boost gauge, there was virtually no lag at all. Just a thrilling rush of speed as the gauge’s curved black bars raced across the dial, the tacho needle flicked towards the 10,000-rpm red-line through the gears, and the ZX headed for the horizon at a seriously rapid rate.
I don’t recall any superbike of similar vintage feeling quite as deliciously smooth and rev-happy as the Turbo, whose addictive feel made my all-too-short ride a riot of hard acceleration whenever the opportunity arose. The blown bike’s true top speed was about 225 km/h, so, ultimately, it wasn’t quite as fast as its GPz1100 sibling (or the more aerodynamically efficient GPZ900R), but it arguably felt sweeter and was just as much fun.
Not that the Turbo was simply about speed, because like all the best 1980s sports bikes it was a useful all-rounder, despite its aggressive image — more like the Ninja H2 SX than the hardcore H2. By modern standards, it felt quite tall and bulky at a standstill, with a relaxed riding position and plenty of legroom. The screen and full fairing were protective, the clip-on handlebars were slightly raised, and the dual seat was large and fairly comfortable.
Controls and instruments were much like a normal GPz’s — with the exception of that small boost gauge above the clocks. Like its normally aspirated stable-mates, the ZX could happily be used for touring, even with a pillion who benefited from a sturdy grab-rail. It even had a centre-stand.
Handling was still pretty good, too; especially for a bike that was hardly a lightweight and whose ageing suspension was inevitably past its best. Like the GPzs of the period, it was a big and heavy machine that required plenty of muscle to hurry it through a series of tight bends. But the Kawasaki was certainly stable, both in curves and in a straight line and had a pleasantly neutral feel to its steering. Fortunately, this bike’s 18-inch wheels had just been fitted with new Avon tyres, which doubtless improved the ride and gave more grip than the bike had when new.
The ZX also proved pretty reliable, dispelling worries that its turbocharger — which spun at up to 200,000 rpm — would soon cause expensive problems. My own doubts had not been removed by my experience on that Austrian launch when the first bike I’d ridden had refused to produce full boost before being put out of action when its drive chain snapped, smashing the crankcases. At least my replacement bike had performed much better.
Fortunately for Kawasaki, the Turbo was much better behaved under normal road use. The turbo unit did, however, require a certain amount of looking after, including oil changes at least every 2,500 km. Owners were also advised to allow the engine to idle for half a minute or so after a hard run, before turning off the ignition, to prevent momentary oil starvation. Looked after in that way, the turbo unit was good for over 80,000 km.
But that wasn’t enough to make the Turbo a sales success, partly because its price was almost identical to that of the GPz1100 and Suzuki’s rival 1100 Katana. Given the choice, most riders went for the safer option of a conventional air-cooled four. That’s if they didn’t spend a little bit more to buy 1984’s real star, the GPZ900R. The Ninja arrived in the same year and showed that superbiking’s immediate future lay not with turbochargers but with more compact, 16-valve, liquid-cooled engines.
Kawasaki’s Turbo had missed the chance to shine that it would have had if the firm could have readied it for production a year or two earlier. But given that the other marques’ turbo bikes had also been commercial flops, even being released several years earlier would probably not have made it successful.
It was the ZX750 Turbo that brought the Japanese manufacturers’ interesting but ultimately futile experiment with forced induction to a close, at least for the next few decades. By the end of 1985, the ZX, like the other marques’ turbo bikes, was no longer in production. At least Kawasaki’s contender had been sufficiently fast and capable to prove the concept could work. And several decades later, it surely helped inspire the firm to create the modern Ninja H2 family, without which the two-wheeled world would be a much duller place.