Suzuki Starts Over

SUZUKI STARTS OVER

CW PREVIEW

A new-generation GSX-R750

ALAN CATHCART

SEVEN YEARS AFTER THE LAUNCH OF ITS GROUNDbreaking, trend-setting GSX-R750, Suzuki has bowed to the inevitable.

Its flagship sportbike for the 1992 model year is the completely new GSX-R750, powered by a liquidcooled engine. For now, this liquid-cooled GSX-R750 (previewed in the December, 1991, issue of Cycle World) will be seen only in Europe. But it not only is very similar to the engine that powers the new GSX-R600, coming to the United States for the 1992 model year, it also is the design around which Suzuki's sporting line will be built for years to come.

With its current 750cc engines making sufficient power for most street riders, and with voluntary or imposed horsepower restrictions becoming more commonplace around the world, Suzuki's need for an all-new, liquid cooled 750cc engine is keyed to the company's character and strategy: That strategy is racing, and the character is to be competitive.

Suzuki has had great difficulty in holding operating temperatures of its air-and-oil-cooled engines to efficient levels, especially in all-out race situations. So in order to be more competitive in production-based racing at all lev els, the company has chosen finally to embrace liquid cooling, which allows much more control over engine tem peratures than the air/oil system.

Suzuki makes no bones about its desire for renewed racing dominance. In fact, it underscored that desire by including in the launch of this important new model a racing version of the new bike called the GSX-R750R. Suzuki representatives say they won't be building com plete R-model Superbike racers for sale, but will instead offer a series of comprehensive race kits, presently under development by the factory.

One thing race tuners probably won't have to do is bump the new engine's compression ratio. It starts out at a sky-high 11.8: 1. Bore-and-stroke dimensions are the same 70 x 48.7mm used by the old engine. But this new motor is smaller than the one it replaces. It's 2.2 inches narrower, for a total crankcase width, including covers, of just 17 inches, and its crankcase center is an inch lower than that of the old motor. This nicely compact engine is mounted

further forward in the chassis than the position called for by the old design, allowing a more desirable forward weight distribution.

The cylinder-head design is also new, with included valve angle narrowed from 40 to 32 degrees, and with camshaft lobes now acting directly on each cylinder's four valves instead of actuation via rocker arms, as before.

These changes all seem to have paid off. Suzuki claims 116 horsepower at 11,500 rpm for the street version of the new engine.

Som~ final notes on the new engine's cooling system: In an odd twist on the old oil-cooling scheme, the new en gine's pistons get sprayed by cooling jets of oil, just as in the old engine; and the separate oil radiator is liquid cooled, to further reduce engine temperatures.

Like the engine, the a1u~inum double-cradle chassis also is all-new, with pentagonal-section upper spars welded to a forged swingarm pivot and sand-cast steeringhead section. An upside-down fork is fitted, as are 12.7inch Nissin rotors squeezed by four-piston calipers. The alloy swingarm departs from normal four-stroke practice by borrowing an idea from two-stroke GP racing, with a conventional box-section arm on the left matched to a flat, pressed-alloy arm on the right. This allows the ex haust pipe to be tucked in more closely, increasing ground clearance as well as narrowing the bike's frontal profile.

That search for a narrow profile underlines Suzuki's intent for this new bike, which was to produce the slim mest, most aerodynamically efficient inline-Four in the 750 class. To help do that, it conducted extensive wind tunnel tests that led to revised bodywork.

With the fuel-injected successor to the Honda RC3O

rumored for late next year, it's a major surprise that Suzuki has opted not to fit EFI on this new bike, instead staying with the familiar 38mm Mikuni carburetors. That decision just might make the GSX-R750 the last 750 sportbike to be launched by any major manufacturer without the bene fit of fuel injection.

But fuel ihjection or not, Suzuki has high hopes for the new GSX-R's combined benefits of liquid cooling, slim build and light weight (even if the exact weight of the new model was not revealed at the launch, and could not be elicited from tight-lipped Suzuki execs). Suzuki brass are confident this new bike will possess sufficient firepower to catapult the company back into contention both in World Superbike racing, which it intends to enter next year, and in the performance-oriented marketplace.

Time will tell how well placed that confidence is.