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Honda VF 750S Sabre
Besides being the wunderbike of 1981, Yamaha's 750 Virago gave new credence to what companies like Harley and Ducati had known all along: that a tandem vee-twin is an almost perfect powerplant for a motorcycle. But now Honda has upped the ante twofold for vee-powered motorcycles with the most important new engine in more than 13 years: the tandem vee-four, an almost perfect powerplant for a motorcycle rider.
Indeed, that odd-looking mass of flat-black and polished alloy nestled in the midsection of Honda's stunning new V45 Sabre (and V45 Magna, as well) is the industry's first-ever liquid-cooled, four-cylinder, 90-degree tandem vee—truly a milestone in the evolution of the motorcycle. Just as that first CB750 inline four back in 1969 long will be remembered as the prototype for the engine of the Seventies, so does the V45 vee-four promise to be the model for the engine of the Eighties.
It's not hard to see why. A proper vee-four can retain most of the assets that have kept the vee-twin a viable motorcycle engine for almost a century (exceptional low-end torque, the potential for perfect primary engine balance, and all the handling/ ergonomic advantages of a narrow motor) and combine them with the most endearing aspects of modern inline fours (the large valve areas and high redlines that lead to the astronomical horsepower numbers that a twin can't equal). In other words, the best of both worlds.
That's an ambitious promise, but one that the Sabre lives up to magnificently. It's armed to the teeth with raw horsepower, enough to land it right in the thick of the 750-class performance wars, yet it slugs out low-end and mid-range torque that would do justice to a one-liter motor. It has none of the heavy, low-rpm power pulsations that can turn a vee-twin into a shuddering blur, nor does it emit the annoying high-frequency vibration that has become the calling-card of many inline fours. And the slimness of the engine (5.5 inches narrower than a CB750F inline four) has permitted a motorcycle that feels light and responsive when turning but reassuringly stable in a straight line.
Well-deserved accolades all. But, in the cold light of performance, the V45 clearly is not superior, either in WFO acceleration or Café-racer handling, to several inline 750 fours, including Honda's own CB750F. But understand that the Sabre is not intended to out-sport the 750F in any way. Instead, this is Honda's attempt to market a 750 that appeals to a broad cross-section of riders rather than catering exclusively to the relatively small numbers of skilled peg draggers and stoplight racers.
Honda's main incentive for building this broad-band motorcycle was an overwhelming dealer / rider request for a shaft-drive 750, ideally something comparable to but more universally appealing than Yamaha's spiffy 750 Seca. The result is a bike that Honda feels is one of the most versatile in its history, a point we can't argue. It certainly is a capable if not a champion canyon racer, but it's still a delight either for daily commuting or for long stints in the saddle, whether they're conducted at wacko lean angles along winding back-roads or in vertical-cruise mode on arrow straight Interstates.
Some would call that sport-touring, which isn't a half-bad way of interpreting where the Sabre fits into the scheme of things. But the truth is that this motorcycle can, within reason, be just about any kind of streetbike its rider wishes, and do it with admirable efficiency. And more than any other part of the motorcycle, the engine is what makes that versatility possible.
When you're in a go-fast frame of mind, for example, the Sabre has enough acceleration on tap to bang out quarter-mile times in the 12.3-second range—a tick slower than some inline fours, a speck faster than others. And while that's respectable acceleration in itself, the V45 actually wings through the gears faster than those times indicate. You see, when the Sabre is being launched off the line, the hydraulically actuated clutch engages rather abruptly and the torque reaction of the shaft drive wants to send the front wheel skyward. Hence you waste a few precious tenths of a second getting the Sabre out of the hole. But once underway, it cuts loose with acceleration that's as vicious as anything the competition has to offer.
Dragracing, though, is a poor barometer of this engine's real-world performance. Because much like a vee-twin, the Sabre has a powerband a mile wide and a torque curve as flat as a tabletop. In any gear and at virtually any rpm, the bike is ready and willing to accelerate at an impressive rate-enough so that no inline 750 can stay with it in a contest of roll-on acceleration. Which is all the more remarkable when ^ you consider that in top gear, the Honda effectively is geared almost 10 percent taller than the average inline 750 four. Because of its wide powerband, in fact, the Sabre's six-speed gearbox almost is a nuisance. It would be no worse off, really, with a five-speed box that used the same top- and bottom-gear ratios as the Sabre's six-speed.
What's most amazing about the Sabre's lugging power, though, is that the engine seems configured to be anything but a torquer. It's a light-fly wheeled , extremely short-stroke, high-revving, high-compression, high-output motor (80 bhp on Honda's dyno, as opposed to 75 bhp for the 750F), all factors which usually impair rather than impart low-rpm grunt. But the engineers have^jj done their homework with valve angles, combustion-chamber shapes, ignition^^ curves and carburetion. The payoff is an ™ engine that pulls like gangbusters from the depths of the rpm basement all the way up to the 10-grand ceiling.
That's a prime example of how the mar-riage of vee-twin and inline-four technologies has fathered what is likely to be the engine of the immediate future. Another is the Sabre's exceptional, almost remote smoothness. The 90-degree vee spread has guaranteed perfect primary engine balance, and rubberized engine mounts dampen out what little secondary vibes the Sabre's ultra-short strokes might generate. That renders the engine so vibration-free that the position of the tach needle often is your only evidence that the thing is even running. And when you do feel and hear the engine it has only a soothing, low-pitched hum reminiscent of a BMW.
Our Sabre also shifted with smoothness and precision, but alas, those same superlatives don't apply to the behavior of the clutch. Because aside from engaging with the aforementioned abruptness, the clutch in our test bike fried itself to a well-done crisp on only its third dragstrip launch. And the replacement clutch threatened to do likewise, forcing enough change in our holeshot technique to raise the ETs. Honda is investigating this problem, the solution to which we will report as soon as we know it. But that failure was not enough to dim our admiration for the Sabre's engine, for we still feel that it is one of the most remarkable and logical powerplants ever to reside in a motorcycle. And it can only get better with the passage of time.
By comparison, the chassis of the Sabre seems almost mundane, although it does boast several noteworthy features. The rear suspension is an air-assisted, damping-adjustable Pro-Link single-shocker; and the front fork incorporates a bolt-on aluminum anti-tweak brace across the tops of the slider legs, plus a TRAC (Torque Reactive Anti-dive Control) mechanism on the rear of the left slider. The double-downtube frame's left-side cradle tube unbolts for easier engine R&R, and that removable section of frame also serves as a coolant delivery pipe to the water pump in the engine.
In terms of critical chassis dimensions, the Sabre differs considerably from the CB750F. It has a 1.5-inch longer wheelbase, a 2.5-degree greater steering head angle and seven millimeters of additional front wheel trail. That's not surprising, however, since a bike with a lower center of gravity (eg) generally needs slowed-down steering characteristics in order to have adequate stability. But you may be shocked to learn that the Sabre's crankshaft actually sits higher in the chassis (by anywhere from .5 to 1.3 inches) than the cranks in the inline fours.
The reason is that not only is it possible to have steering geometry that's too quick, the the eg can be too low, as well. Either condition can leave you with a bike that turns corners with lightning quickness but is much too easily diverted off-course when traveling in a straight line. And since Honda wanted a do-everything 750 and not a nervous purebred racer, the Sabre had to be made stable as well as nimble. So its dimensions were stretched out and the engine was not specifically designed to locate the crank (usually the heaviest part in the engine and the component around which everything else must be positioned) as low as possible. Anyway, since the front cylinders are almost horizontal ahd the short stroke yields a low cylinder height-plus the fact that the engine weighs 10.5 pounds less than a 750F motor—the eg is plenty low.
You can't fully appreciate just how low, though, until you give the Sabre a decent workout on a twisty road. It's rock-steady at high speed in a straight line, yet is perfectly willing to be tossed over into a hard turn at the slightest intentional provocation. The machine feels lighter than its 511 pounds, a sensation that is most apparent when you flick it from side to side through a fast S-bend—or slightly overshoot a corner and have to find that extra little bit of lean angle. And there's enough cornering clearance to make banging any of the undercarriage off of the pavement decidedly difficult, especially when the suspension is on its firmer settings.
With that kind of low-effort handling going for you, aided by the endless torque output of the motor, it's easier to maintain a seven- or eight-tenths pace in the twisties aboard a Sabre than on any of the inline 750s. You can develop a smooth, fast rhythm for sweeping into and out of the corners gracefully without a lot of gearshift tap-dancing and bodily athletics. But unfortunately, working yourself up to around nine-tenths starts asking more of the chassis than it can deliver; and ten-tenths just flat feels uncomfortable. The rear end then wallows around a lot, especially when the throttle is snapped shut or the superb brakes are tapped when the bike isn't perfectly vertical. In short, you quickly become aware that the Sabre is not the answer to a canyon racer's prayers.
It's difficult to pinpoint the exact reasons for this less-than-brilliant behavior; but much of it seems to stem from a mild shortage of rebound damping in the rear shock, and so the rear end can pump up and down too freely under the load of hard cornering. And the typical chassis gyrations induced by the shaft drive just contribute to the problem—although Honda has, through the use of a longish swingarm and relatively short wheel travels, minimized that behavior.
Don't forget, though, that the Sabre is meant to be more than just a definitive corner-bender, and as such, the finer points of its handling have been somewhat dulled in the process. But if the handling was compromised to enhance the long-distance comfort quotient—which it undoubtedly was—it's a shame that the bike doesn't ride better. It soaks up the bigger, rolling bumps nicely, but the littler chops and ripples defeat the suspension altogether. So any illusion of ultra-smoothness created by the state-of-the-art engine is too often shattered by the suspension's inability to respond to small, abrupt inputs.
That lack of compliance, and the engine's inprudent use of fuel (39.9 mpg average, five to seven mpg less than on the typical inline 750) are, however, the only things that seem incongruous with the Sabre's long-distance aspirations. The seat, for instance, doesn't feel particularly comfortable at first, but it nonetheless manages to keep you from squirming in pain when you have to park atop it all day. Neither is the riding position necessarily ideal for
long-haul luxury (grips and pegs a bit high in relation to the seat), but it's not off the mark far enough to bring about any significant discomfort.
Boredom, though, can take its toll on -those long rides; so for your entertainment f[ out on the road, the Sabre has a full com-plement of high-tech LCD instrumentation (see story, pg. 55). High-tech also aptly describes the Sabre's F.O.I.L. (Fiber Optic Integrated Lock), the most sophisticated anti-theft system ever included as standard equipment on a motorcycle. It consists of a special steel security cable that plugs into a small self-powered control box on the left side of the bike. The cable has a light-transmitting fiber optic inside, and if it is cut or unplugged without first switching off the system with the ignition key, a loud beeper is activated. And since the system depends on the light passing through the fiber optic, the cable cannot be "jumped" with a piece of electrical wire. _
That could prove invaluable on a motor-^ cycle that's as likely to become prime burglar-bait as the Sabre. But if this bikei truly does end up on every moto-rustlerV most-wanted list, it will have gotten there strictly by dint of its engine. For if the vee-four were plucked out of the chassis and replaced with any modern inline four, the Sabre would then be just another pretty face, a nice motorcycle that looks good but does nothing exceedingly well other than stop easily and contrallably.
With the vee-four, though, the Sabre is exciting, competent and just plain pleasant. Because in every area of performance that is even remotely dictated by the engine, the Sabre forces no compromises, allowing the rider to have his cake and eat it, too.
So there's no doubt about it: The motor is the message on the Sabre. And what it's telling us is that tandem vee-fours are about to become a staple in the motorcycle supermarket. Soon. Very, very soon. •
Source Cycle Guide 1982