In the first half of the nineties the class 750 it was probably the benchmark for the production sports models with a four-cylinder engine.
The world championship Superbike he was also living a period of great popularity and even there to monopolize the attention and interest of enthusiasts were, in addition to the Ducati twin-cylinders, whose displacement now exceeded 900 cm3, the four-cylinder 750.
Kawasaki has focused decisively on this class, with excellent models intended for road use and now also designed with a view to eventual competitive use.
The latest evolution of the 68mm bore and 51.5mm stroke engine was used in the ZXR 750 (i.e. ZX 750 H) presented in Cologne in 1988 and marketed since the beginning of the following year.
The engine changed very little compared to the original version, which appeared with the 750 GPX. The central distribution chain remained while the head that now housed was different cup tappets instead of finger rockers.
The chassis was completely new, with double beam aluminum frame completed by a removable lower cradle, very similar to that of the ZX-10 entered production a year earlier.
The big airbox was powered by two corrugated pipes of considerable section that received the fresh air (as it is not heated by the passage through the radiator) by two sockets made in the front part of the fairing.
A great bike but it soon became clear that something more was needed to be truly competitive.
Akashi’s engineers then designed a model with a completely new engine, which went into production in 1991. The bike was always called ZXR-750 but now it was made in two versions, one of which had significantly higher performance. The latter was also known, on certain markets, as ZXR 750 R and had a power of 121 CV a 11500 giri/min (while the other had 100 HP).
The engine had several characteristic sizes, with a bore of 71mm and a stroke of 47.3mm and actually best represented the state of the art of the time in the field of very high performance series engines. The timing chain was placed on the right side and the crankshaft rested on five bench supports. The angle between the two planes on which the valves lay (with a diameter of 29 mm at the intake and 25 mm at the exhaust) was only 20 °, an authentic record value.
The eccentrics acted on finger rockers and the cylinder block was of the type open deck, with dry-applied cast iron liners. The new frame, always with a double supporting beam, was now without the lower cradle.
In the Superbike version this bike has come to deliver about 150 cavalli at a speed of 13800 rpm, corresponding to 200 hp / liter and at an average piston speed of 21.8 m / s. It was about excellent performance, which allowed a Scott Russell to bring it thrice to success in Daytona 200 miles and to establish itself in the 1993 Superbike World Championship.
This extraordinary 750 has also conquered four Endurance Championships.
In 1993 the Kawasaki 750 was revised, but the engine remained virtually unchanged. The “tuboni” have disappeared and a suction system with one has been adopted single dynamic grip large, obtained in the front left part of the front of the fairing, to the side of the double headlight. A sort of effective dynamic supercharging was therefore obtained, with the airbox being put under pressure by exploiting the forward speed of the bike, when the latter was very high.
The motorbikes of the world superbike in 1994 were equipped with a cascade distribution control of gears, to return to the chain later (due to regulation).
A real revolution took place in 1996. To make the new one ZX-7, proposed in versions R e RR, in fact, a complete redesign was carried out.
The characteristic measurements have increased to 73 x 44.7 mm (with a stroke / bore ratio of 0.612, a record for the 750 four-cylinder engines) and the angle between the valves has been increased to 25 °.
The cylinder block has become a closed deck, with re-applied wet barrels of the type with upper support edge. In the head the finger rockers have been replaced by cup tappets. The inlet valves had a diameter of 28.5mm and the exhaust valves 24.5mm.
In the cycling part, a double supporting beam frame in aluminum alloy was maintained, without a cradle and with a design similar to the previous one and stood out the brake calipers, now six-piston.
The RR version dispensed 122 CV a 11800 giri/min and had a maximum rotation speed of 12800 rpm (1000 rpm of “draw”, therefore before the limiter came into operation). The specific power was 168 hp / liter and the mean effective pressure (PME) reached 12.4 bar.
Also in this case, a version destined for Superbike races was obtained from the production model, which was developed to reach a power of the order of 170 horsepower at nearly 15,000 rpm, corresponding to over 225 hp / liter and a PME of 13.6 bar.
However, this was not enough to make the Kawasaki 750 a winning bike again; the competition had a little more. Superbike was going through a period of crisis, with fewer participants and a certain loss of interest from fans and the media. This has led those responsible for organizing the World Cup to modify the regulation, bringing the displacement of the quads to 1000 cm3.
Kawasaki has lost interest in the SBK championship for a few years and has focused its attention on the races of the 600 Supersport, with results that were soon extraordinary. (He follows)
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