1996 Kawasaki Zx-7r
1996 KAWASAKI ZX-7R
IS THIS THE MACHINE TEAM MUZZY NEEDS TO DEFEAT DUCATIS?
KAWASAKI'S 750 SPORTBIKE DEVELOPMENT IS INCREMENtal, not revolutionary, but any update from these masters of refinement is always big news. It brings fresh capabilities to riders, and illuminates the future of motorcycle engineering.
1996 sees changes made to the ZX-7’s engine, chassis, suspension and aerodynamics. Two forces drive these changes: 1 ) The mad onrush of technology, Japan’s favorite marketing tool; and 2) the need to take back the World Superbike crown from Carl Fogarty and Ducati.
Team Ducati has been able to enlarge its 851 engine towards the lOOOcc limit (for Twins), but Kawasaki can only refine its package and try to rev the 750 Four everhigher. More rpm has failed to make more power in the present design, despite friction-reducing techniques such as piston, rod and bearing downsizing being used to the full. Therefore the new-for-’96 engine cuts stress at a given rpm level in the classic way: by reducing the stroke. The 6-perccnt change from the former 47.3mm down to 44.7mm might also be used to raise the existing race-engine rcdline beyond 15,000 rpm. Street rev limit for the new ZX will be 12,800. The larger, 73mm bore no doubt offered challenges in the combustion department.
The cylinder head receives a suite of changes. First, the four intake ports are now' equally spaced, so they approach their valves symmetrically. This assists intake How by not favoring one valve of a pair at the expense of its mate. Intake-port diameter is downsized from 40 to 36mm to increase velocity. Higher How velocity helps midrange power and, given proper shaping, does not hurt top end. Intake-tract length is shorter-necessary to complement higher rpm. To permit closer mounting of the carburetors, the method of valve actuation has been changed from lever (wider) to inverted bucket (more compact). Although I had suspected at the Laguna Seca World Superbike round that the new model might incorporate geared earn drive, the new ZX retains Morse chain drive at the right side of the engine.
Another area of redesign is engine interior fluid mechanics. Pistons in this engine rise and fall in 180-dcgree pairs, 1 and 4, 2 and 3. Even though total crankcase volume remains approximately constant, air is rapidly pushed back and forth between these two cylinder pairs. Local pressure variations push air back and forth between cylinder head and ease, through restricted passages. This not only takes power, but interferes with steady oil return from head to ease. Therefore larger drainbacks are provided between cylinders 2 and 3, and extra pressure-equalizing passages have been created.
Engine width is a problem any time bore size is increased. Before, the iron cylinder liners were shrink-fitted into the aluminum cylinder block, which was surrounded by the water jacket. In the new design, the block is an “empty box” in which the bare liners themselves stand exposed to the cooling water, retained and sealed only at top and bottom. Such wet liners improve cooling and permit larger bores to fit in the same width.
A new ram airbox is fed from openings at either side of the twin headlights, and a new fairing and front fender provide low drag and improved airflow to the now-curved coolant radiator.
Chassis progress means taking the ilex out of the frame, and putting it into the suspension, where it can be controlled accurately. Kawasaki says this perimeter frame’s stiffness is the highest it has yet built. Side-beam section is increased 5mm, but this increases stiffness more than you’d think-torsional stiffness increases as the 3rd power of diameter. The rigid-mounted engine braces the chassis in diamond fashion. Large hollow axles contribute further stiffness to this package, a Kawasaki technique since 1975.
Suspension is as adjustable as on any racebike, with both the new 43mm inverted fork and rear nitrogen-pressurized single damper providing a wide range of compression and rebound settings, with ride height and preload adjustment. The racer-oriented or “homologation special” ZX-7RR offers a slightly heftier rear damper, and more focus on fine compression damping adjustment.
The limited-edition ZX-7RR has additional special features: Oat-slide 4lmm Keihin carbs with accelerator pump and enrichment circuit; close-ratio transmission; heftier crank; adjustable swingarm-pivot position and steering geometry. The fork is specially finished to cut stiction, and
front calipers of increased piston area are fitted.
Kevin Cameron
