Kawasaki ZX 750

Bike India - - CONTENTS - WORDS: ROLAND BROWN PHO­TOG­RA­PHY: PHIL MAS­TERS

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.

Rear sus­pen­sion duty han­dled by a Uni-Trak shock-ab­sorber

Air-cooled, 738-cc turbo-four ar­rived late but was mighty fast

Note the anti-dive sys­tem on the fork

In­stru­ment clus­ter was sim­i­lar to the GPz; boost gauge was unique, though

Un­like the com­pe­ti­tion, Kawasaki placed the turbo up front

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