Kawasaki ZX-11 Ninja
Source: Cycle, March 1990
You could make the argument that Kawasaki started the horsepower war with the Z-1 in 1972, and that the company fully intends to end the superbike skirmish once and for all with the 1990 ZX-11 Ninja. Kawasaki has always hung its hat on the performance hook, yet even company executives wonder where superbike performance could possible go from here. The pre-production ZX-11 you see here is so fast and so powerful that it opens a whole new window of reference for street bike performance.
In just three days, the ZX-11 Ninja smashed every high-performance record in the book. On day one, Kawasaki's shimmering black bullet hammered the quarter-mile in 10.52 seconds at 132 mph. On day two, it pumped out 127 rear-wheel horsepower on the dyno. On day three, it went full ballistic, rocketing across a dry lake at 175 mph. This machine is the speed freak's midnight fantasy, a ride on the blast wave of an endless explosion.
Here is a motorcycle that fires from 0 to 132 mph in 440 yards, front wheel skimming the asphalt, a wisp of blue smoke trailing its humongous 170/60 rear tire. With Kawasaki's own ZX-10 pumping out 118 horsepower, Yamaha's current FZR1000 hovering at 115, and Suzuki's GSX-R1100 at 108, the ZX-11 -at 126.6- is the most powerful street bike Cycle has ever tested. This is a motorcycle that will spin the rear tire as easily at 80 mph as it does at 30. You want to talk top speed? No stock street bike has ever broken the 170-mph barrier, yet the ZX-11 recorded 175 mph on our speedgun. Forget about basking in the communal warmth of motorcycling. This is a bike for kicking ass.
In a U.S. market under fire from bureaucrats and safetycrats bent on thwarting the great "bullet-bike" menace, the ZX-11 Ninja is a towering monument to Kawasaki's corporate cojones. Still, Kawasaki's U.S. reps are understandably gun-shy about the black beast. Says Mike Vaughan, communications director for Kawasaki Motors Corp., U.S.A., "We didn't ask for this motorcycle."
Nonetheless, ZX-11s will begin rolling off Kawasaki's Lincoln, Nebraska, assembly line alongside the ZX-10 in time for the 1990 spring thaw. Quantities will be limited to about two bikes per dealer. At $7599, the ZX-11 is at the pricely end of the superbike scale, but Kawasaki could likely peddle the 11's otherworldly performance for 10 grand a pop without raising an eyebrow. In addition to its power, the ZX-11 is remarkably civilized, with comfortable seating, convenience features expected in the class, and a fairing that rivals the aerodynamics of a Learjet. The engine is surpassingly smooth at all rpm and remarkably quiet - not at all what you expect of a motorcycle that is still accelerating hard enough at 130 mph to flatten your eyeballs.
At a glance, you might mistake the ZX-11 for the ZX-10. Both bikes share similar silhouettes, but only a handful of parts are interchangeable. Though based on the ZX-10 engine, the ZX-11 mill -at 1052cc- offers 55cc more displacement via a bigger bore; redesigned intake and exhaust systems; big, 40mm carbs forcefed by ram air induction; and an entirely new aluminium chassis bristling with upgraded suspension, wheels, tires, brakes, and the most aerodynamic fairing kawasaki says it has ever produced.
To cope with the additional power, Kawasaki bolstered the ZX-11's bottom end. A new crankshaft has 1mm larger diameter crankpins. Chrome-moly connecting rods, carburized for additional hardness, provide extra strength while being 32 grams lighter than the ZX-10's carbonsteel rods. Kawasaki's faith in the durability of these rods is evidenced in the ZX-11's 10,500-rpm redline - up 500 rpm from the ZX-10's. With the same 58.0mm stroke, the elevated redline pushes the ZX-11's piston speed well past 4000 feet per minute.
Elsewhere downstairs, the 11's clutch gains durability through thicker, larger diameter plates, and radially grooved drive plates that increase oil flow for greater cooling and fade resistance. Primary drive gearing is 5 percent taller than the ZX-10's; and while internal transmission ratios remain unchanged, second, third and fourth gears are machined out of nickel chrome-moly for greater strength. To increase cooling capacity while maintaining a narrow frontal area, the ZX-11 gets a convex radiator similar to that of Suzuki's GSX-R750/1100. The ZX-11's six-tier oil cooler, borrowed from the domestic 400cc Zephyr, helps keep the ZX-11 running in the temperate zone, as well.
How did Kawasaki engineers manage a 10 percent horsepower increase over the ZX-10 with only 6 percent more displacement? Remember, the basic building block of this liquid-cooled, four valve engine traces its origins back to the original 900 Ninja of 1984, and two generations of Ninja 1000s. Kawasaki engineers have lived with this engine for a long time, and they know how to make it sing.
The began by pressing 2mm larger liners into the ZX-10 aluminium cylinder block. Inside this 76mm bore are concave pistons that create a spherical combustion chamber with the same 11.0:1 compression as the ZX-10's. Kawasaki holds tolerances so tight that the ZX-11's pistons need no stabilizing skirts below the wristpins, and that makes these slugs 4.5mm shorter and 12 grams lighter than the ZX-10's pistons.
From the head gasket up, the ZX-11 is patterned after the ZX-10, but no parts interchange. Like the ZX-10, the ZX-11 uses Kawasaki's most advanced valve train. In this system, each valve has its own separate finger follower. For valve clearance adjustment, each follower slides sideways against a spring that holds it in place on the pivot rod, exposing the adjusting shims with the camshafts still in place. Not only is this system convenient, it's also lighter (27 percent lighter than Kawasaki's previous screw-type system), and compact enough to permit a narrow, 30 degree included valve angle, and steep intake ports that dump straight into the combustion chambers.
In the ZX-11, Kawasaki hogged out the intake and exhaust ports, and capped them with bigger valves -intakes up from 30 to 31.5mm, exhausts up from 26 to 27mm. Like the ZX-10, the valve stem area is tuftrided -a variant of nitriding- to increase wear resistance. And, of course, Kawasaki hand-matches the intake ports to the valve seats for maximum flow. With new camshafts, the 11's bigger valves open sooner and close later, adding 4 degrees of duration on the intake side, 6 degrees on the exhaust side. Bolted to the exhaust ports is a new four-into-one-into-two exhaust system, which Kawasaki claims boosts low and midrange power while offering the volume needed for high-rpm running. Two-millimeter larger semi-downdraft Keihin carbs feed the intake.
With the ZX-10, Kawasaki produced the most efficient cylinder head the company had ever made. High intake velocity through smallish downdraft ports and large valves increased the ram effect of the fuel charge pouring into the cylinder. The result was high flow at low engine speeds, and a broad powerband with high peak output. In the ZX-11, Kawasaki has taken the next logical step in the same direction: Ram Air Induction.
Ram-air systems have been widely used in automobile applications, but the ZX-11 is the first production motorcycle to be fitted with such a system. The ZX-11's is simple: Air enters a duct just below the headlight in the lower lip of the fairing, and passes through a long snorkel to a huge, 15-liter airbox beneath the fuel tank. Because the airbox and snorkel eat up valuable fuel space, Kawasaki tilted the ZX-11 engine forward 2 degrees (17 degrees from vertical) to provide a larger fuel-tank capacity. Tilting the engine forward has other benefits, as well, such as lowering the center of gravity, and increasing front-end weight bias for better handling.
Unlike other "fresh air" systems that merely direct cool air into the engine bay -such as that used on Suzuki's GSX-Rs and Kawasaki's own ZX-7- the ZX-11's ram air is a closed system: The front inlet duct is the only source of incoming air to the airbox. This sealed system accomplishes two things: First, it creates a ram effect that pressurizes the fuel mixture through the carb throats, and increases intake velocity. Second, it provides a steady diet of cool, dense air by completely isolating the carbs from engine-heated air.
Airbox ducting alone creates a pressure rise in the carb throats only; without also increasing float bowl pressure, the engine would merely lean out and run poorly as pressure in the throats increased. Early reports had the ZX-11 fitted with an electronic fuel-management system, but Kawasaki engineers found a far simpler -and lest costly- solution: They vented the bowls to the incoming air source -the mouth of the duct- through a tube that boosts bowl pressure as airspeed and intake velocity increases.
Drawing cool, dense air into the engine increase power across the board. But because the intake pressure created by the ram-air system is governed largely by incoming airspeed, the ZX-11 must be moving at high speeds before the system has a significant effect on power. The Kerker dyno, equipped with two-speed cooling fans rated at 45 and 85 mph, showed the effect of airspeed on the ZX-11's power.
With the fans at 45 mph, the ZX-11 ran as much as three horsepower stronger from 3500 to 7000 rpm than with the fans at 85. Conversely, the 85-mph head wind created a boost in power from 8500 all the way to 11,000 rpm, where the ZX again ran three horsepower stronger. Obviously, Kawasaki calibrated the system carefully: The ZX makes its biggest low-end and midrange numbers at low road speed, while high-speed running nets the biggest top-end numbers. Judging by the ZX-11's 175-mph top speed, we suspect the ram-air system may pay even greater power dividends at ultrahigh speeds.
No matter how you measure it, the ZX-11 is stronger everywhere than current superbikes. In a class where small percentages separate the winners and losers, the ZX-11 boasts hugh advantages. From 4000 to 7000 rpm, for example, the ZX-11 runs 19 to 29 percent stronger than the ZX-10 and FZR1000. At 7500 rpm, the ZX-11 is already into triple-digit power, and by 8000 rpm it towers over the ZX-10 and FZR by a whopping 20 horsepower. At its 126.6-horsepower, 10,000-rpm peak, the ZX-11 is 8 horsepower up on the ZX-10, 12 on the FZR. More impressive than the ZX's peak power is the quality of its delivery: There are no discernible dips or flat spots anywhere in the curve, nor is the ZX-11 the least bit peaky. From 8500 to 11,000 rpm, the ZX-11 never dips below 121 horsepower.
With that kind of power on tap, it's not surprising that the ZX-11 beats other superbikes in the quarter-mile. But top speed on the level of the ZX-11's requires more than brute force. For that, Kawasaki engineers gave the bike gearing and aerodynamics that augment the engine's powerband.
Void of even a single color stripe, the black fairing comprises three large sections of ABS and PBT plastic. Using fewer sections of bodywork may prove more costly in a tip-over, but fewer seams increase surface slickness. A flush-fitting headlight, integrated turn signals, and a large-coverage front fender smooth airflow. Wider, more blunt-nosed than the ZX-10's bodywork, the ZX-11's fairing is Kawasaki's slickest yet, boasting (according to Kawasaki) 10 percent less total drag than does the ZX-10. But the ZX-11's aero-approach goes beyond the shell. To reduce frontal area, Kawasaki trimmed fork length and travel, dropping the ZX's nose 10mm. Seat height is down 15mm to set the rider deeper into the cockpit, out of the wind for less drag.
The result of the ZX-11's carefully orchestrated formula is top speed that eclipses the ZX-10's -the previous top speed king- by nearly 10 mph. The ZX-11 feels less at odds with the environment at triple-digit speeds than anyhing we've ridden. At 100 mph the ZX-11 is loafing; 120 feels like the right cruising speed.
Despite its outer-limits capability, the ZX-11 is perfectly at home in everyday environs - smoot, easy to ride, perfectly civilized. A contra-rotating balance shaft, spinning in the bow of the crankcase, makes the engine a genuine smoothie, the six-speed transmission snicks easily through the gears, and the motor warms quickly in the morning. The only glitch in the ZX's engine manners is noticeable driveline lash, made more pronounced by a flat spot in the carburation just off idle. We suspect that this flat spot - combined with supertall, 188-mph gearing - also explains the ZX's middling 45-70 mph roll-on performance, though the 11 easily outsprints the ZX-10 in roll-ons.
The ZX-11's operating zone is a bit higher than those of other superbikes. Here you are, going along at 60 mph. Brrrraaaappppp... here you are at 130 - just like that. Rolling on the throttle can drive you stark raving euphoric: Every millimeter of throttle movement seems to bring another 20 horsepower to bear. The engine has enough power to overwhelm the rear tire exiting corners - even in the higher gears and with excellent traction - and accelerates hard enough to lighten the front end as the speedo blurs past 100 mph. You learn in a big hurry to be precise, careful, respectful.
You also learn to appreciate the ZX's excellent chassis. Though it looks similar to the ZX-10's, not a single component is interchangeable. The wall thickness of the aluminium perimeter frame's extruded "e-Box" upper main beams has been increased to 4.0mm for greater rigidity. The swing-arm-pivot bulkhead features hollow, box-section construction with a central wall for greater strength. The swing arm proper uses thin-wall construction with a central rib, the nassive aluminium beams measuring 90mm (up 10mm from the ZX-10) by 30mm, and terminating in huge, eccentric chain adjusters.
Suspension and running gear are just as serious. A new fork with thinner walls and larger-diameter stanchion tubes - up from the ZX-10's 41mm to 43mm - increases rigidity and steering precision. Travel is down 10mm to 125mm, but sophistication is up thanks to threaded spring preload and four-way rebound damping adjusters atop each leg. In back, Kawasaki's Uni-Trak linkage compresses a sophisticated, gas-charged, aluminium-body shock with remote reservoir. Threaded preload collars and a four-position rebound-damping dial provide adjustment.
Wheels, brakes, and tires are new items, as well. Up front, dual semifloating discs - borrowed from the ZX-7 - measures 310mm in diameter, and are gripped by a set of four-piston Tokico calipers. The rear brake is a dual-piston unit. Unlike the ZX-10, which rolls on a 17-inch front, 18-inch-rear wheel combination, the ZX-11 has 17s at both ends, each shod with Dunlop's newest low-profile radials. Front tire and wheel size remain the same as the ZX-10's, but the racer-wide 5.5-inch rear wheel mounts a monstrous 170/60-VR17 Dunlop that measures nearly 7 inches across the thread.
The engine overwhelms every impression of this machine: Ride the ZX-11 down a favorite stretch of road, and chances are you'll never think about the rest of the bike. Part of this is because the chassis works exceptionally well, and because the ZX-11 is in some ways less imposing than the ZX-10.
Though the ZX-11's frame shares critical dimensions with the ZX-10's - same 58.7-inch wheelbase, 26.5-degree rake and 101mm trail - it feels smaller, more lithe. Wet weights - 575.5 for the 11, 578 for the ZX-10 - don't explain the difference. The ZX-11 redistributes that weight lower and farther forward, and that makes the 11 feel less formidable at low speeds. A shorter, narrower fuel tand and 15mm lower seat make the ZX-11 feel less massive, and cut the stretch to the handlebars.
Ergonomics remain roomy, with more legroom than other sport bikes have, and a seating position that puts the rider into a moderate tuck without stressing arms and wrists. You can ride this motorcycle all day without wishing for more comfort. The cockpit is superslick, with an inner cowling that houses a small storage compartment and surrounds large, analog instruments - including a 200-mph speedo. All the niceties are here - self-canceling turn signals, bar-mounted choke, and knurled adjusters on the clutch and brake levers. Without the aid of a petcock or a fuel gauge, however, the rider relies on a set of bright red low-fuel warning lights, and not one but two tripmeters to signal a pit stop. Highway cruising nets 45 mpg - about 235 miles between fill-ups - but heavy throttle hands can suck that figure down to 35 mpg, or even lower, and bottom the tank 50 miles sooner.
The fairing offers good protection from wind and engine heat, with no discernible buffeting; and there's ample room for dipping inside the bubble, though peering through the distorted windshield gieves the world an udersea look. The passenger finds relatively comfortable quarters on the one-piece, dual-density seat, though the small grabrail is better suited to a less powerful machine.
That's about the only chassis component that't not a match for the ZX-11's power. The brakes offer good feel and feedback, and enough stopping power to haul the ZX down from 60 mph in 124 feet. Traction from the Dunlops is excellent, and the ZX has abundant cornering clearance to feather these big skins to their edges. Combined with superwide wheels, the round-profile Dunlops make steering a bit heavy on tight canyon roads, but the ZX-11 is more agile and far more neutral-steering than the ZX-10. Gone is most of the 10's tendency to stand up under braking, and this allows the ZX-11 to be braked deeper into corners, with more confidence.
As you might suspect of a 175-mph motorcycle, the 11 has suspension calibrated to "firm". Over sharp bumps, rear suspension response is harsh, and softening rear spring preload does little to improve the ride, The fork is more compliant, thoug it, too, telegraphs harshness to the handlebar over rippled pavement. We suspect Kawasaki gave the ZX-11 a hefty dose of compression damping to help stabilize the chassis. Indeed, the ZX is rock-solid, stroll-in-the-park composed at ludicrous speeds. On backroads, it has a stability and sure-footedness few motorcycles can match. That, with 127 horsepower on tap, makes for serious backroad momentum.
But the real fascination of the ZX-11 lies in the breadth of its ability. On the one hand, the ZX-11 Ninja is a sledgehammer capable of pounding everything else flat. On the other hand, it's a wonderfully refined, impeccably finished, broad-spectrum sport bike you could savor every day without ever reaching deep into its perfomance envelope. In this sense, the ZX-11 is a natural progression of the ZX-10, an extension of Kawasaki's all-purpose superbike vision.
But the ZX-11 Ninja is really much more than that. It is the most powerful production motorcycle money can buy, a 175-mph street bike that looks sinister as hell, a machine that will send the safaty Nazis into a frenzy just as surely as it will bring Kawasaki fans to their feet. In a world where horsepower limits are increasingly the norm rather than the exception, superbikes are fast becoming an endangered species. The ZX-11 is the most remarkable superbike we've ever ridden. If it were also the last, it would forever be enough.