The styling went smooth and curvaceous with this model with
almost everything being new - 73.0 x 44.7mm short-stroke motor, thinner
piston rings, bigger main bearings, bigger valves, new high-lift camshaft,
36 mm contant-velocity semi-flatslide carbs and up rated suspension, wheels
and tyres. All this produced 112 hp at 11,000 rpm to propel a dry weight of
195 kg. Unfortunately, it lost significant ground clearance (via the
exhaust) and the adoption of 17" wheels which offered only a slim margin of
error.
Every detail of the chassis and engine of the GSX-R down to the single bolt
was reevaluated for the new 1988 model. The fairing was redesigned for 5.7%
less frontal projection and 11% lower drag. The wheelbase at 1400mm made the
GSX-R the most compact bike in the class. The lightweight aluminium alloy
frame incorporated 45mm box tube main section and the cast swing arm pivot
resulted in 60% more ridity. Front fork stanchion tubes were increased to
43mm diameter with variable damper adjuster type inner rods. The back end
featured full floating suspension with new linkage and needle bearing for
smoothness. Opposed 4 piston brake calipers, new weight-saving
hollow-typecast wheels, and wide Michelin radial tyres became new standard
equipment.
The distinctive air-cooled with SACS engine received
larger diameter oil hose and less restrictive joints for 20% increase in the
coolant flow and the large 15 row cooler improved the cooling efficiency by
48%. The red zone started at 13,000 rpm. Engine bore and stroke changed from
the previous 70 x 48.7mm to shorter stroke 73 x 44.7mm to reduce
reciprocating motion mechanical loss. The new Slingshot carburetors were
equipped with lightweight throttle valves for increased throttle
responsiveness. Another important addition was the incorporation of SACI
(Suzuki Condensed Air Intake) system bringing fresh air from ducts on the
front of the fairing to the carburetor intake for maximizing cylinder
charging efficiency.
Lighter and simpler than the 34mm flat-slide units they replace, the 36ers
use a slide, round in front and flat in back, which, like the "cartridge" fork,
was pulled from Suzuki's RM motocrosser trick bag. Racers in search of the
perfect mixture will appreciate the ease with which the Mikunis can be rejetted.
With a one-piece plastic float and needle assembly, changes can be made quickly,
with no tiny parts to drop out on the ground and disappear. A metal tang sets
float height with similar ease.
Spark comes from a new computer-controlled electronic ignition, similar to
the 1988 Katana and Intruder systems. Analog rpm signals from the crankshaft are
digitized by the computer, which pulls the optimal ignition advance from a
selection of ignition curves developed through dyno research, and programmed
into a random-access memory chip. Up to 5000 rpm, the curve is tracked and
adjusted through 125-rpm increments up or down the rev band. Above that, the
computer takes a reading with every 1000-rpm change in engine speed. To better
withstand the violence of lower-volume, higher-compression (10.9:1) combustion
chambers, the GSX-R gets fire from dual-electrode NGK JR9C spark plugs. When
engine speed ventures past the 13,000-rpm redline, an electronic rev limiter
cuts power.
The 748cc engine packs one cubic centimeter less than before; bore and stroke
shift from 70 x 48.7 to 73 x 44.7 mm this is the most oversquare Suzuki street
four yet. With a shorter stroke, the new configuration drops piston speed
accordingly; at 10,000 rpm, J-model slugs travel 2993 feet in the same minute
1987 H-models move 3195. Despite extensive drilling around the edges and
undersides of the wrist-pin bosses, the J's larger-bore slipper pistons are each
12 grams heavier than the old 750 slugs.
Larger bores mean a new and slightly larger cylinder casting to maintain liner thickness, overbore capacity and
heat transfer characteristics. There's a new crankshaft spinning down below,
with journal diameters bumped two millimeters to withstand the greater loads of
higher rpm. The crank gains 10 ounces in the process, despite lighter flywheel
weights. Connecting rods measure 106mm, 3.5 shorter than those in the '87
engine.
Though general layout is unchanged, tuning in this engine is Early American
Hot Rod; that is, hotter cams and larger valves. The 28.5mm intakes and 25.0mm
exhausts are both GSX-R1100 spec. Intakes stay open 16 degrees longer than the
old 750's did; exhaust poppets 24 degrees longer. Overlap jumps almost 32
percent to 75 degrees. The valve adjustment interval is every 4000 miles after
the initial 600; lash is taken up by a standard screw-and-locknut layout.
In order to get a free-breathing engine quiet enough to be legal, Suzuki resorted to a four-into-two exhaust system.
The dual mufflers and additional piping add seven pounds and subtract ground
clearance, but they deliver tuning latitude that Suzuki pushed to the maximum.
Here is the first mass-produced 750 delivered with an 11,000-rpm,
90.75-horsepower peak, actually a horsepower more than the GSX-R1100. Formerly
the 750-class dyno king (85.33 hp at 11,500 rpm), Yamaha's FZ750 loses by better
than five ponies. The race-replica FZR fares no better with 83.76 at 10,500.
Anyone else? Making a tick under 83 horsepower at 10,500, the Kawasaki 750 Ninja
can't compete. Without a sporting 750 in the lineup for 1988, Honda's 1986
Interceptor gets summarily snuffed on the dyno as well, its 82.55 horsepower
best buried under the J-model's stratospheric power curve.
With superimposed dyno charts, the new 750's curve lies at a steeper angle than its predecessor's. Though the
old engine posts a two- to four-horsepower advantage between 3500 and 4000 rpm,
the J pulls even at 5500, three horsepower beyond at 6000. Both curves angle
near 62 horsepower between 8000 and 8500, but they part company at 9000 where
the J wakes up, flying higher above the '87 bike as revs climb. Peak to peak,
the J really gives its stepsister's dancing shoes a trampling—this engine is
11.5 horsepower stronger than the old 750.
Suzuki's air/oil SACS cooling system moves 6.1 quarts of oil (15 percent more
than before) from a deeper sump, through a higher-capacity, two-stage trochoidal
pump and a large-capacity oil cooler, which Suzuki claims disposes of 48 percent
more heat. New lines and fittings are said to be good for a 20-percent jump in
oil flow, and a dished baffle improves cylinder-head cooling by keeping the flow
pumping so hot oil doesn't sit around getting hotter. Oil descends to the sump
via two large return passages cast into the front of the head and hollow
front/center cylinder studs.
Does the new GSX-R's more conventional strategy of high power beat last
year's low-mass approach? Yes and no. Weighing in at 493 pounds soaking wet, the
1988 GSX-R750 pushes the scale 27.5 pounds further than the '87 bike, yet the J
remains the lightest Japanese 750 currently available.
Where does the weight come from? The engine is 11 pounds heavier; tack on 15
for the frame; then add heavier wheels, tires and exhaust system. Even pulling
5.4 pounds for every peak horsepower, the 750J still carries about a half pound
less per horsepower than last year's GSX-R.
It's the old big-motor Superbike formula, and it works in the quarter mile:
Our test bike's best run down the drag strip took 11.04 seconds. More important,
it blistered through the traps traveling 122.41 miles per hour, a single mile
per hour slower than the GSX-R 1100. That's a tick quicker but 7.6 mph faster
than our last GSX-R750's best 11.33/ 114.79-mile-per-hour run.
This huge difference explains why Suzuki went for a pumped-up engine and let
the low-mass ride. Top speed on the order of the J's takes horsepower, lots of
horsepower, and this bike, with just a touch more traction, could certainly get
into the 10s. Surprisingly, roll-on numbers were almost identical to those from
our 1986 test unit.
The J took 122 feet to stop from 60. That's surprising, considering that the
GSX-R's stopping hardware appears as if it was lifted from Kevin Schwantz's
Superbike and feels supremely powerful. But the Michelin A59 front tire, with a somewhat triangular profile, lays down a narrow contact patch under
straight-up braking, and the J, without an anti-dive fork, suffers nosedive
under hard braking. Also, as in drag-strip tests of acceleration, very small
factors the feel of a particular bike, traction feedback, even a rider's daily
bravery index can account for such differences. Despite the middling numbers,
the GSX-R brakes are excellent stoppers powerful and predictable.
Suzuki held the GSX-R750's coming-out party at Laguna Seca Raceway, a track
whose high-speed, gravity-bowl turns and knotty pavement surface place ground
clearance and correct line choice at a premium. At Laguna the new bike did
everything more quickly and easily than the old: stop, go, turn—and drag the
ground. Since six of Laguna's nine turns are left-handers, the clearance problem
was concentrated on the bike's left side, where pipes and fairing threw sparks
and plastic shavings—the sidestand, before, it was removed, smacked the pavement
violently. Time to dial some ground clearance into the 750's suspension.
The truth that this Suzuki is as sensitive as it is keenly focused—became
apparent with only a few turns of the 750's myriad suspension adjusters. A dozen
click stops at the top (rebound) and bottom (compression) of each fork leg alter
damping rates. Fifteen millimeters of spring preload—in 2.5mm increments— are
available via a 14mm bolt atop the fork. The shock is simpler—preload adjusts
via a threaded collar, rebound damping with a four-position wheel.
From a standard setting—with compression set six clicks from bottom; rebound
out seven—we increased compression damping two positions, rebound one more click
in, and dialed in all 15 millimeters of preload. Getting more ground clearance
out of the GSX meant more shock preload as well. Two turns proved too stiff; 1.5
was a workable compromise. Shock rebound damping went full stiff.
Without an independent ride-height adjuster, the GSX-R really forces a
compromise between optimum suspension settings and maximum ground clearance.
With the Suzuki you take—are forced to accept—the lesser of two undesirables:
quirky handling and better ground clearance, or correct handling and little
daylight left under the bike. Stiffening the GSX-R's shock exaggerated the
already steep steering angle, making the bike's front end less trustworthy
through Laguna's tricky downhill turn eight. Stripped of its sidestand, the
J-model continues to drag pipes and fairing solidly on the ground.
Handling/suspension trade-offs aside, the GSX, with strong acceleration,
powerful brakes and adjustable suspension, is still a machine most at home on
the track. The Michelin 59-series radials fitted, however, are better suited to
the street. With the recommended 36 psi pumped in front and rear, the Michelins
easily carry traction to the limits of the GSX-R's ground clearance, but the
rear is a little hard—the bike's back wheel spinning under acceleration out of
slow corners. The Suzuki, with its wide-gauge wheels, suffers from a shortage of
tire choices. Real racing slicks, or perhaps taller radials, might well ease the
GSX's ground-clearance problems. At the moment, the Michelins are the only tires
designed to fit the Suzuki's 17-inch super-hoops.
When the GSX returned to the Cycle shop,
it was instantly evident that the racetrack setup was too stiff for street
riding. We softened the fork's rebound damping to eight clicks out; compression
to seven, with preload chopped in half—to 7.5mm. The shock lost two turns of
preload, and damping was set midway at two. With these adjustments, the fork's
bump response improved, but the Suzuki stood up in corners under braking and,
thrown hard into a fast downhill corner in a nose-down attitude, pushed its
front end.
Suspension setup—especially in a motorcycle as
sensitive and complex as the GSX-R—is a matter of subjective choice, dependent
to a large degree on variations in rider size, weight, expertise level, etc. To
balance the chassis and get more ground clearance, two of Cycle's
staffers—with wet weights ranging from 155 to 190 pounds—lowered the fork tubes
one quarter inch in the triple clamps from their standard setting with tubes
protruding up one-half inch. Steering neutrality returned and the tuck
disappeared, along with the bike's tendency to stand up under hard braking.
Our 140-pounder had different, priorities:
Without suspension compliance to keep the tires planted, he reasoned, what good
is ground clearance? He dialed up the fork's softest compression setting,
screwed in a single click of rebound, left preload at 50 percent and sunk the
fork tubes still further flush with the top of the triple clamps. Shock preload
was backed off half a turn and rebound damping set at three.
Pulling the Suzuki's nose up though it did slow
steering response a bit was one compromise everyone agreed on: Fork tubes stayed
put at flush while our 187-pound man dialed three millimeters of spring preload
(one more than stock) into the fork and set compression and rebound damping at
seven and six clicks out respectively (both stock). Out back, the shock was
stiffened a half turn past standard and rear rebound was left at three.
Setup on the GSX-R is an arduous, exacting
process. Stock settings are probably the best compromise for most riders, and
altering them without a trail of notes to get back to normal is pure folly. But
on the right road, the results are magic. As long as the stock pipes, fairing
and sidestand remain where they are, though—which is mostly on the
ground—clearance will continue to be the limiting factor with this motorcycle.
But let's get one thing straight: Serious,
complex and demanding as the GSX-R is, it's best understood as a road-legal
racer—a "street bike" that's as far removed from the street as Laguna's
corkscrew is from Sunset Boulevard. On this 750, straight pavement becomes
almost a perversity. The old GSX-R suffered from racetrack ergonomics; the new
bike's seating is more severe— higher pegs, harder seat and lower bars, ^ut
while the old GSX-R was otherwise an excellent street machine, fast and
forgiving, the J-bike is pure edge. It'll daunt most duffer racers. Complex as
the GSX-R's suspension is for a street bike, the hundreds of choices its
suspension offers—with more opportunities for error than delight—are only
average for a track-competitive machine.
There are some niceties, though, some civilities
to the beast: It warms quickly and runs more smoothly and quietly than the old
GSX. Reined in between 70 and 75 miles per hour in top gear, its solid-mount
engine is vibration free, easing freeway flights between the twisties. But the
GSX cooks your kneecaps in heat from the fairing; the mirrors match size with
effectiveness—very little. A full tank lasts about 190 miles; 50 more than most
riders will.
That's because the GSX-R750 is a motorcycle for
true believers. Counting yourself among them means you couldn't care less that,
for the Suzuki's list price, you might easily buy more street bike. But your
dollars could never capture this much street-legal Superbike racer, and—at
$5199—you can bet they never will again.
Source Cycle World 1988
Any corrections or more information on these motorcycles will be kindly appreciated.