Yamaha FZ 750 Genesis

Yamaha's modern generation of superbikes began in 1985 with the FZ750. Much more than just a superb machine with a level of all-round performance unmatched in the 750cc class, the FZ introduced the engine layout of four angled-forward. liquid-cooled cylinders, each with five valves, on which Yamaha's big bike range would be based for many years to come.

The FZ's 749cc motor was a revelation. Tilting its cylinders forward at 45 degrees moved the centre of gravity forwards and downwards, and also made room for an innovative breathing arrangement. The bank of Mikuni downdraft carburettors sat where the cylinder head would normally have been. The airbox was shifted forwards to a new position just behind the steering head, and the fuel tank extended down into the space normally occupied by the carbs.

This gave a large volume of cool air with a straight run down to the engine - where it met the unique sight of three tiny inlet valves to each cylinder. Yamaha claimed the five-valve layout gave significant benefits over four-valve designs, mainly because although the total valve area was slightly smaller than with two larger inlet valves, the trio's total circumference - more important, because the valves were almost always only partially open -was larger. The figures were promising, with a peak output of 105 hp @ 5000rpm.

The FZ750's chassis was designed to complement the engine layout but was conventional, based around a frame of square-section steel tubes, rather than the aluminium of Suzuki's rival GSX-R750. Front forks were air-assisted and. like most sporty set-ups at the time, held a 16-inch front wheel. Rear suspension was by vertical monoshock. Styling was smart but conservative, with an angular half-fairing that left the black-finished motor on display.

And what a motor it was. When Yamaha had announced the 20-valvc layout the previous year, cynics had commented that it was a complex gimmick that gave no benefit over the normal 16-valve design. Some had second thoughts after riding the FZ750. whose combination of engine power and flexibility would have been impressive for a large-capacity bike, let alone a compact and easy-handling 750.

No matter what engine speed was being indicated by its tachometer, the FZ surged smoothly forward when its throttle was wound open. Even from below 2000rpm it responded cleanly, when most larger-engined bikes would have hesitated. By 7000rpm in the highest of its six gears the Yamaha was already close to 100mph (16lkm/h) and pulling hard. Then it kicked again, moving into warp speed and pushing its rider back as it headed for a top speed of over 140mph (225km/h).

Chassis performance was less spectacular but still very good. Handling was stable and precise. The fairly upright riding position combined with the excellent suspension to give comfortable highspeed cruising, although the screen was quite low. Other practical features included a generous fuel range, and the fact that the valve train not only proved very reliable, but required adjustment only every 28,000 miles (45.000km).

Apart from a twin-disc front brake that lacked power compared to its rivals, the FZ was an outstanding machine: fine-handling yet reasonably comfortable: rapid but remarkably tractable: aggressive in looks and feel, yet well-equipped and as suited to everyday riding as almost every other Japanese four. Unfortunately for Yamaha, it did not achieve the sales success it deserved, even when uprated a year later with a full fairing. But as the first of many great 20-valve fours the FZ750 was one of the most influential bikes of its generation, as well as one of the best.

GSX-R750 vs FZ750

FIFTY FEET AHEAD. THE SUZUKI GSX-R750 banks into the corner, leaning until just inches separate its high-mounted footpegs from the road. Early morning light streaming through the trees dances across the GSX-R's sculptured surfaces, alternately illuminating its rider, then returning him to the shadows. His back is curved into a tuck, hands low on the clip-ons, elbows bent, weight shifted up against the tall gas tank and off to the inside of the turn. Trailing behind, the rider on the Yamaha FZ750 watches the GSX-R's smooth arc through the corner, its rider's knee skimming just above the asphalt, and he's reminded of racetracks, of racing heroes, of photographs depicting their skill. The howl of the Suzuki's engine pulling through 10,000 rpm as the bike thrusts out of the corner does nothing to dispel those images.

The two riders have found the rhythm of the road, and they play tag as it wraps up the side of the mountain. The Suzuki's rider works harder at the handlebars to roll the GSX-R into corners, but once on its line, the Suzuki tracks through the turn with unflappable stability. The rider on the FZ750 has it easier; the Yamaha flicks into the corners like a much smaller and lighter machine, and its incredible mid-range power launches it out of them as though another 150 or 200cc were at work in its engine. On this crisp, mountain morning, both riders, piloting the two highest-performance 750s available, are having the time of their lives. At this moment, riding these two motorcycles is the best thing in the world.

The exhilaration and enjoyment of that morning began last fall at the Cologne motorcycle show in Germany, where these two extraordinary motorcycles made their first public appearance. They were were the stars of the entire show, displaying leading-edge technology and boasting the kind of performance that promised to set the rest of the 750 class on its ear.

Shortly thereafter, during test rides on pre-production versions of these two revolutionary machines, we saw for ourselves that the promise of performance made at Cologne was no hollow threat. The FZ750, which we tried at Willow Springs, was amazingly quick, with a surprisingly broad powerband and light but stable handling. We later rode the GSX-R at Suzuki's test course in Japan, and found it to be at least as fast, considerably lighter, and capable of performing just like the race bike it was designed to be.

Both bikes seemed light-years ahead of the 750 class. But the inevitable questions kept cropping up: Which of these two new-wave road-rockets is the best? Which one will set the new standard of performance for 750cc sport motorcycles?

Those questions could be answered only by directly comparing these two bikes, by putting them together on the same racetrack, the same dragstrip and the same U.S. highways and backroads. But doing so right now posed a problem; for while the FZ750 was released for U.S. consumption in early spring and the GSX-R750 made its debut in Canada, Japan and Europe slightly thereafter, the Suzuki isn't slated to hit these shores until the end of the year. And we didn't want to wait. So we contacted a local "gray marketeer," Jack Calof of Exotic Motorcycle Imports, and before long, a Japanese-spec GSX-R appeared on our doorstep.

But even that bike posed a problem: 750cc motorcycles sold in the Japanese home market are limited to a 77-bhp output, compared with 105 bhp on models exported to Canada and most parts of Europe. So we had to acquire the OEM parts needed to bring the GSX-R up to the unrestricted specs of the Canadian model—a different air-filter element, a set of recalibrated carburetors, a slightly different exhaust system, and different tires. Even with that, our test GSX-R was different from those that will come into the U.S.; to comply with this country's emissions regulations, U.S models will likely be equipped with CV carburetors instead of the flat-slide carbs on our test bike, and there will be minor changes in the gas tank and trim as well.

But all in all, those differences should not significantly alter the Suzuki's performance; they possibly might even improve it for this market. Which means, then, that our GSX-R was representative of what you can expect from an American-spec model. It also means that this test-the world's first head-to-head comparison of the Suzuki GSX-R750 and the Yamaha FZ750—is meaningful to potential buyers of either bike.

Both the FZ750 and GSX-R750 started as fresh ideas. The Yamaha's history dates back farthest, to late 1977 and a research project whose goal was to design a four-stroke engine that could compete in racing on an equal basis with two-strokes. That desire, barring turbocharging, leads in one direction only—higher engine speeds. To make more power in wholesale quantities, a four-stroke must spin faster. And because the number of cylinders is limited by racing rules, that higher-rpm capability can come only from using shorter and shorter strokes with larger and larger piston areas, along with a valve train that will both stay alive and flow enough mixture to support those high engine speeds.

Yamaha's answer to a valve train that would support the 20,000-rpm-plus operating speeds required was to use many small valves. Honda had come up with the same answer, but chose a very different solution with its oval-piston, eight-valve NR grand prix four-stroke. Yamaha stuck with a conventional round bore, but squeezed four intake valves and three exhausts above it. Piston rings presented no problem as the NR Honda's had, but cooling the thin sections between the center exhaust valve and its two mates was troublesome, along with the simple difficulty of actuating the multiple valves and finding locations for all the ports.

But Yamaha's engineers made it work (on a test bench if not on an actual motorcycle); and when it came time to build a knock-the-competition-dead 750 sportbike, they were primed to use their new technology. But not in all its seven-valve-racer purity, and not even for exactly the same reasons. Because along the way, they had discovered advantages of valve-multiplication that went beyond merely allowing high engine speeds. They learned that many small valves could also help in building an engine that combined excellent peak power with a strong mid-range. The secret wasn't in achieving fantastic flow rates with the valves fully open; instead it was in using the large amount of valve circumference, along with the fast opening speeds possible with small valves, to obtain high average flows during the entire time the intake valves were open. Cylinders could be filled with mixture through this high average flow rather than depending on the long period of port opening given by radical, long-duration camshafts. The result? More power everywhere.

To achieve these benefits in an engine that could be easily produced meant fewer than seven valves. Instead, Yamaha engineers configured a combustion chamber with five valves—three intakes and two exhausts. This allowed a central sparkplug and a lens-shaped combustion chamber with good burning characteristics, permitting a high, 11.2:1 compression ratio to be used even with low-octane gasoline.

Yamaha also had to find the best engine configuration to wrap around this new combustion chamber. V-Fours were dismissed as too bulky, and a conventional inline engine was rejected for being too wide between the rider's knees. So the engineers elected for an inline-Four with a difference: The cylinders canted forward 45 degrees, and downdraft carburetion mated with nearly straight-shot intake ports, ports that may have as much to do with the engine's power as the multiplicity of valves. Every effort has been made to keep the engine narrow (16.3 inches across the cases), with the alternator mounted on a jackshaft behind the cylinders, and ignition pickups that fit directly into the sides of the crankcases, triggering off notches cut in the outer crankshaft flywheels.

By comparison, the chassis is straightforward, with trendy box-section tubes sweeping around the sides of the engine to the swingarm pivot, rather than wrapping over the top. Because of the downdraft carburetors, the front of the gas tank is essentially a hollow shell covering the airbox. The gas hides in the back of the tank, and in the tank extension that sticks down into space that would normally be filled by carburetors and airbox. A 16-inch wheel is used on the front, with an 18 on the back. A 16-inch rear (as used on the FJ1100) was disdained because the selection of rear racing tires available in that size is limited; and one of Yamaha's goals is to have the FZ win production races.

That same goal, perhaps pursued even more vigorously, was responsible for much of the GSX-R's design. Suzuki's concept for the GSX-R was simple: to be as close to a race bike as possible. Specifically, it should be a street-going replica of a 24-hour endurance racer, a motorcycle that could establish a strong performance image for Suzuki in the sport-intensive European market.

Etsuo Yokouchi, head of Suzuki motorcycle engineering, set two specific targets to ensure that the racer-replica tag would be more than just decals affixed to swoopy fiberglass. The GSX-R would have to be uncommonly light (388 pounds without any fluids was Yokouchi's goal) and it woul-d have to be powerful, over 100 bhp. High targets to be sure.

At 423 pounds with all fluids except gasoline, the GSX-R is slightly overweight by Yokouchi's standards. But by anyone else's, it is stunningly light, with so little mass that it almost needs to be tied down. Not only is it the lightest 750 sportbike by more than 60 pounds, it is lighter than either an FJ600 or a 600 Ninja, and only six pounds heavier than a Honda VF500F. Where the excess poundage was pared is difficult to see; obviously, the aluminum frame is lighter than a steel one, but that, according to Suzuki, reduced overall weight by only 21 pounds. The rest came from where weight reductions always come from: everyplace. Each individual part was examined, and either was redesigned to be slightly lighter or eliminated entirely if it wasn't really needed.

Similar thoroughness has been applied to finding horsepower in the engine. Power gains over previous Suzuki 750s came from longer-duration cams, bigger valves (made possible by small, lOmm-diameter sparkplugs), more compression, and less curvature in the inlet ports, as well as other, more subtle details. As an example, Suzuki's careful stress-analysis of pistons and rods allowed unnecessary material to be identified and removed, reducing their weight. That, in turn, allowed main- and big-end bearing sizes to be reduced; and the smaller bearings have correspondingly smaller frictional losses_, to the tune of three horsepower at 1 1,000 rpm. With the aid of these subtle factors along with the dramatic, Suzuki claims to have squeezed 105 bhp from the GSX-R.

Keeping the engine cool while making over 100 horsepower has required one deviation from standard motorcycle engine practice: The GSX-R engine looks air-cooled but actually depends on a special oil-cooling system to drop the temperature of internal hot spots. A high-volume, low-pressure oil pump feeds oil jets that are directed down on the tops of the combustion-chamber crowns; and oil passing through the big-end bearings is squirted up at the bottoms of the piston crowns. The oil picks up heat from these areas that are difficult to cool with air, and then loses that heat when it passes through an oil cooler that's practically the size of a water radiator. Suzuki chose to develop this oil-assisted cooling system because its engineers realized that meeting both the weight and power goals set by Yokouchi would be difficult without it; they estimated that liquid-cooling would have been 14 pounds heavier, and they were concerned about reliability with a pure air-cooling system.

While the GSX-R's engine is your basic hot-rod 750 with innovative cooling, its chassis closely follows endurance-racing trends. Eighteen-inch wheels are used front and rear, a departure from recent sportbike practice. The reason is that 18-inch tires last longer than 16s and the larger diameter front rim allows the front wheel to be changed without pulling the brake calipers. These both are important factors in a long endurance race where tire changes are expected, but not desired any more often than necessary. Also, slightly slower steering may be a benefit for an endurance bike, especially when a tired rider has to cope with a wet, slick track at 3 o'clock in the morning.

ON THE ROAD

First impression of the GSX-R comes while unloading it from the truck: This machine is light. It even rolls easier than other motorcycles of its displacement. A brief ride on nearby streets does little to dispel that impression; even with 25-inch-wide clip-on handlebars, the GSX-R steers lightly at city street speeds, and it flips from side-to-side effortlessly.

Once out on a road strung together with higher-speed curves, however the Suzuki steers more heavily, almost slowly. The rather long front wheel trail, the 18-inch front wheel, the roadrace riding position and especially the clip-ons work together to mask the bike's extraordinary lightness.

Neither does the power delivery seem indicative of the bike's absence of weight. The engine pulls smoothly, with the best power starting at 8000 rpm and extending to the 11,000 rpm rev limit, but it doesn't come in with a sudden, peaky kick. Instead, the power just gets stronger and stronger as engine speed increases. The return springs on the flat slide carburetors are strong, though, and twisting the throttle requires an unusual amount of effort for a Japanese motorcycle. And that high-effort throttle, along with the high-effort steering, makes the GSX-R seem less responsive and less capable than it actually is. It simply requires rider muscle to be ridden fast.

Switching to the FZ on the same road is quite an experience; how can two motorcycles so similar in size and purpose feel so different? The seating position on the FZ is pretty much standard sportbike: lowish, cast handlebars requiring a slight forward crouch, footpegs directly under the rider's weight and not terribly high. By comparison, the GSX-R clip-ons require a more dramatic tuck and a straight-arm riding position, and the footpegs are further aft and closer to the seat than those on any other streetbike sold in this country. The Suzuki's gas tank is large and projects straight up from the front of the seat. It's molded to the shape a rider takes in a full racing tuck and is designed to support him in that postion. The GSX-R in effect wraps around the rider; on the Yamaha, the rider sits on top. The FZ's gas tank and seat are narrow, and make it much easier for a rider to shift his weight around.

There are even more differences in engine performance and handling characteristics. The FZ engine fpulls adequately, although not exceptionally, from the very bottom of its rev range; but when it reaches 5000 to 6000 rpm, it leaps ahead with a surge of mid-range power and pulls hard all the way to its 11,000-rpm redline. It will handily defeat the GSX-R in any roll-on contests that start at engine speeds below 8000 rpm, and its light throttle pull makes it feel more responsive yet. But mostly because of the FZ's tremendous mid-range, a rider placed on the Yamaha without being told its displacement might well guess it to be at least a 900, maybe bigger. But on the GSX-R, he would know that he was on an exceptionally powerful 750.

Handling is noticeably quicker on the FZ as well, partially due to its 16-inch front wheel, and partially because of its slightly wider and higher handlebars. Accordingly, the FZ is much more willing to change lines in a corner. Again, if the rider didn't already know the weights of the two machines and had to judge only from a trip through a 60-mph S-bend, he probably would think that the Yamaha were the lighter. The downside of the FZ's quickness is that it doesn't have the Suzuki's stability when planted on a cornering line; the GSX-R feels as though an act of God would be needed to get it headed somewhere the rider didn't want it to go.

There also are some substantial differences in comfort between the two bikes. The FZ's suspension is compliant and quite pleasant for a sportbike's, and the riding position is near-perfect for all-around rising. The seat, however, is narrow and less than ideal for a long ride. The GSX-R's seat is actually better, but the rest of its ergonomics, as well as its firmer suspension rates, are more suited for a racetrack than for the street. The GSX-R is tolerable for medium-length freeway trips and other rides on which the wind pressure can relieve some of the load from the rider's arms, but even a short trip through city traffic puts a heavy burden on wrists. And the pegs are always too high for anything short of racetrack work, often causing cramping.

AGAINST THE CLOCK

Neither of these two sportbikes was designed with dragstrips specifically in mind, but a quarter-mile run still tells much about their relative performance. And on a cool, slightly damp evening at Carlsbad raceway, the Yamaha ripped through the standing quarter in 11.53 seconds at 116.88 mph. The strong mid-range made the bike easy to launch, but keeping the front tire near the ground through first gear was difficult.

Preventing wheelies proved to be an impossibility with the GSX-R; it picked up the front wheel at the beginning of each run and didn't set it down until the shift into second. But even though our tester had to back off slightly to keep the bike from flipping over, the GSX-R still turned a best quarter of 11.48 seconds at 118.26 mph. And there seemed to be more performance left. During dragstrip starts, the rider had to try to find the perfect balance between using too much rpm, which would result in an excessive wheelie, and too little rpm, which would bog the engine. If the nearest replacement clutch hadn't been 6000 miles away in Japan, we would have experimented more to find that perfect balance. As it was, the GSX-R's terminal speed approached that of open-class streetbikes, and the FZ was only a slight, but significant, click slower.

Braking tests resulted in more mono-wheeling, this time on the front wheel. While stopping from 60 mph in 125 feet, the GSX-R spent most of its time with the rear tire just off the ground. Due to the Suzuki's light weight, the combined center of gravity of rider and motorcycle is higher than what is normal on other 750s. Combine that with a sticky front tire and a short wheelbase, and "brakies" can result. The FZ750, while less dramatic in its braking, managed excellent stops, the best being 117 feet from 60 mph. Nevertheless, the Suzuki's front brake provided better feel and confidence.

Our final testing of these two race-inspired street machines took place in a fitting venue—Willow Springs Raceway. And to ensure that both machines were stretched to the fullest, we enlisted the aid of Doug Toland, a California club racer who has of late been dominating the streetbike classes at that track, turning times on a production 600 that are more appropriate for a superbike. But despite our best-laid plans, one last difficulty arose prior to the testing at Willow: The Suzuki's rear tire got punctured on the way to the track, and there was no exact replacement available in the United States. Instead, we replaced the European-spec OEM Bridgestone (V-rated) with the Japanese-spec OEM Bridge-stone that had originally been on our test bike (same size and tread pattern, but H-rated), and hoped the rubber compounds were similar.

That wasn't the case, for the GSX-R's lap times at Willow were hindered by the rear tire sliding excessively and too early. Despite the tire, though, the GSX-R lapped Willow at 1:40.0, and Toland was impressed. The GSX-R felt like a real racebike to him, and its stability, its hard drives out of the corners, its front brake, and its ability to slide controllably all were exceptional. The only real problem was a soft spot in the carburetion at 7500 rpm that caused a sag in the power at that speed, making gear selection critical.

Not that the FZ wasn't just as impressive. After dialing in the suspension (10 psi in the fork, rear shock preload set to the No. 3 position, shock damping on its highest setting), Toland rounded Willow in a 1:38.4 aboard the FZ, which is an outstanding time for a 750 on stock tires. The FZ's broad powerband made it easy to ride, but because only a narrow rev range is needed on the racetrack, this was less of an advantage there than on the street. The FZ's quick handling made transitions into corners easier, but the bike may have moved around a hair more through bumpy, high-speed Turn Eight. But the handling of both the FZ and the GSX-R was excellent.

The most telling comment came when Toland was asked which of the two he would choose to race. Regardless of the times recorded during this test session, he was convinced that he would go faster on the Suzuki than on the Yamaha if they were both fitted with the latest Michelin production-racing tires. He cited the Suzuki's outstanding high-speed power, its racer-like feel and handling, and its superior brake feel. But he thought it would be close, and that both bikes would be capable of rounding Willow in the 1:34 range when wearing the latest tires. He felt that the outcome of a race between the two would depend as much on rider skill as on the capabilities of the bike.

CONCLUSIONS

For sheer performance, the Suzuki GSX-R can't be beaten. It's quicker and faster than the Yamaha FZ750, if not by much. The combination of light weight and high power can't be overcome on the strength of Yamaha's five-valve engine technology alone. But at the same time, the Suzuki's configuration as an endurance-racer replica has forced some substantial compromises in the bike's overall performance. The Suzuki feels like a race bike on which someone has done an exceptionally thorough job of conversion, making it into a streetbike by adding lights, an effective muffler and some padding to the seat. But it's still a racer at heart, and as such it makes demands on its rider that go beyond those made by a typical sportbike. Its seating position is extreme and uncomfortable for anything but full-bore blasting. What's more, the Suzuki's biggest advantage—its light weight-is effectively masked by the slowish steering geometry and low-leverage clip-ons. And its engine feels less responsive than it should because of the heavy throttle-return springs.

But whereas the Suzuki hides its assets, the FZ750 hides its liabilities. The five-valve-per-cylinder engine makes power that belies its 750cc displacement, and the FZ's light handling conceals the fact that the bike is not particularly light in weight.

In the end, the GSX-R is more than a little reminiscent of Suzuki's 1000/1100 Katana: Both are image bikes aimed at the far fringe of sport riders. Both offer exceptional performance, and both punish their rider's bodies in the process. And just as the Katana led to one of the best motorcycles of recent years, the GS1100E, so, too, should the GSX-R spin off some wonderful, less extreme, new Suzuki models.

In the meanwhile, both the FZ750 and the GSX-R are excellent motorcycles for racetracks, or for playing tag up sunlit mountain roads on crisp Sunday mornings. But if you're looking beyond a race, or past the Sunday morning ride, the FZ750 is the best sportbike available.

Source Cycle World 1985