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Honda CX 650TC Turbo
Promises, promises. In 1983 three of the Big Four manufacturers unveiled the world's first production turbocharged motorcycles, heralding the dawning of a new age in two-wheeled travel. It sounded too good to be true; sure enough, it was. Turbochargers on the boost gave middle-displacement machines wondrous power, yet the trade-offs resulted in a net loss. Two shortcomings—limp-wristed power off the boost and annoying turbo lag—handicapped the first-generation turbos. Though these machines showed promise, they weren't functionally superior to 1100cc Superbikes. The turbo bikes were successful despite their turbocharged engines, not because of them. How green these first-year efforts were has become apparent in their second year of production. Honda's 1983 CX-Turbo is vastly improved, enough that some riders will consider the 650 Turbo a viable alternative to a normally aspirated 1100cc sport bike.
Many of the 500TC's shortcomings arose from its modest displacement; off the boost it felt somewhere between a normally aspirated 250 and 400. Honda has logically increased the displacement of the CX-Turbo, and as a 650 the CX-T has considerably greater off-boost power than the old 500 or the Yamaha and Suzuki 650 Turbos. Consequently, the Honda is a pussycat in town. Once the engine hits the boost, however, the CX turns into an absolute animal with stunning mid-range punch. In roll-on contests from 60 mph against the Superbike King, the Suzuki GS1100, the Honda easily jets away. That, friends, makes the CX650T the all-time roll-on champ.
Like the other 1983 CX/GL V-twins, the 650 Turbo displaces 674cc on an 82.5 x 63.0mm bore and stroke. Honda engineers also bumped the Turbo's compression ratio, further increasing off-the-boost power. The CX500 Turbo made do with 7.2:1 pressure, the 650 Turbo runs 7.8:1, and, for comparison, the normally aspirated GL650 has a 9.8:1 compression ratio.
The CX650T's valves are larger in diameter than the 500's: 32mm intake and 28mm exhaust compared to the 500's 31mm and 24mm poppets. As before, the CX uses four-valve heads and pushrod-actuated valves, but the 650's intake valves have greater lift than the 500's, and the 650 intake ports and injector bores are further enlarged. Airbox volume is also up.
To feed the larger engine, Honda enlarged the IHI turbocharger: the 650's compressor wheel is 51mm in diameter, up three millimeters from the 500's, while the exhaust turbine remains 50mm in diameter. The 650's waste gate begins to open at 16.4 psi of boost, down one psi from the 500. Nevertheless, the Honda has impressively high boost pressure.
Last year's CX-T had a dazzling array of fail-safe backup elements built into its turbo and fuel injection systems. This year the factory engineers simplified and rationalized the 650's control systems. They incorporated the ignition-curve control system into the main fuel injection computer, and dropped a number of safeguard components, including an air pressure sensor, an ignition sensor and the resonance-damping "Helmholtz" chamber. The fuel-injection computer has picked up the extra tasks with little detriment to engine operation.
One notable exception is starting. Although last year's Turbo started eagerly, hot or cold, the 1983 version starts reluctantly when cool. Unlike the 500, the 650 has a choke lever; in reality, this lever opens the throttle butterfly valves a crack and lets the computer adjust fuel mixture. When the CX is cold the starter button actuates an enriching circuit. Our 650 required a bit of cranking in the morning, and it stumbled under low throttle openings until reaching temperature. Once warm, the CX starts hesitantly at times, but it runs cleanly. Aside from the low-speed, cold-engine glitch, the Honda meters fuel accurately.
rider had to allow for the Turbo's leisurely pickup when turning in front of oncoming traffic or leaving stop signs. The 650 CX-T has adequate, though not impressive, power before hitting the boost, and enough off-idle strength to handle walking-speed parking-lot duty. This improvement in low-end power complements the new Turbo's taller overall gearing and wider fourth/fifth jump.
Seriously, though, nobody buys a Turbo to plonk along at trials-riding speeds. People buy Turbos for that onthe-boost rush of big horsepower. In this, the Honda surpasses every other bike on the market. The 1983 Turbo changes make the 650 CX-T much more rpm-dependent than the old version; as engine speed increases, turbo lag decreases proportionally. Lag might last as long as two seconds if you hit the throttle when the engine is lugging way down low, but only a second passes when the engine is turning around 5000 rpm. At 6000 rpm and above, power arrives instantly. At all rpms, when power comes on the boost it arrives suddenly, forcefully and unmistakably. Nothing matches the CX650T for mid-range power.
The Turbo's savage immediacy is a mixed blessing for serious sport riders. Like last year's bike, the 650T works best on wide-open backroads filled with broad, sweeping, high-speed turns, where you have plenty of working room and can see far ahead to plan cornering strategy; the Honda's huge power surplus is breathtakingly fun, and reduced turbo lag makes the 650 a joy to ride fast. The CX-T also works well on moderately tight roads. When the 500 fell off the boost, it simply crawled out of tight corners. The 650, in contrast, accelerates reasonably well at low boost pressure, and comes on power much sooner than the 500. On these tighter roads, though, too much throttle will cause a strong and abrupt shift from off-boost to on-power that makes the rear end drift out in mid-corner. The Turbo rider must adapt: When the CX starts to come on the boost he must nick the throttle back to avoid the sudden power surge, then slowly redial to feed in power controllably. These demanding power traits divided our staffers: some worked easily around the Turbo's demands; others never completely adapted to the CXT's power delivery. Everyone could ride the Honda briskly down backroads, but some never trusted the CX enough to step up the pace. Even with the improved engine characteristics, the CXT's turbo-related power will hinder all but the most talented riders on extremely tight and twisty roads. Though yards ahead of the 500 Turbo, the CX650T engine remains less flexible than a big normally aspirated powerplant.
Substantial improvements to the Turbo's suspension components upgrade the CX's backroad handling markedly. On the 650T, the TRAC-equipped 37mm air-adjustable fork has a brace connecting its legs and stiffening the front assembly. Greater rebound damping (40 percent stiffer than last year) was a much-needed change. Last year the 500 had a nonadjustable shock; now the Pro-Link rear suspension system features a shock with three-way adjustable rebound damping. The 650's lightest setting matches last year's single damping rate—a good compromise setting but insufficient for hard sport use; the new number two setting stiffens damping 14 percent, the number three setting 29 percent. Honda engineers also increased shock compression damping a whopping 4.4 times. These combined changes make the CX-T much more stable and taut-feeling than before.
The 650 CX-T exhibits no hobby-horsing through fast, bumpy corners—it handles winding roads with a composure the 500 lacked. With eight psi in the fork, 40 psi in the rear shock, and the damper set on number four, the CX carves through fast canyon roads with hardly a bobble. Through 100-mph-plus sweepers, the 650 shimmies just a wisp—nothing to raise your pulse rate above its backroad level. On knotty roads, the
Honda can be cumbersome; at 571 pounds fully gassed, the CX weighs as much as an 1100cc sport bike, and the CX-T's 58.9-inch wheelbase makes it just a touch shorter. The 650 Turbo feels as if it carries a lot of weight high in the chassis; this, together with the nature of turbocharged power, can prevent the CX-T rider from feeling relaxed when the road becomes as tight as scrambled pasta. Only a deft throttle hand and a good sense of timing will overcome that clumsy feeling and allow a rider to begin to exploit the 650T's power.
The 650's triple disc brakes are quite good, though they fade with brutal use. The front dual-disc offers strong stopping power directly proportional to lever pressure, and lever pull is solid. Honda's excellent anti-dive fork valving system—we set the TRAC adjusters on the number four (heaviest) position and left them there—enhances the Turbo's above-average ground clearance. Eventually, the exhaust pipe hits on the right side, and the centerstand tang scrapes on the left.
The new Turbo Honda also serves admirably as a long-distance mount. Soften up the damping and air-adjustable suspension components, and the CX delivers a remarkably plush ride—not Gold Wing caliber, but close. An excellent seating position adds to the Turbo's freeway comfort, and a new handlebar cures one minor complaint we had with the 500T Our tallest rider (six-foot) felt a touch cramped on the 650, but other staffers loved the seat/peg/bar relationship. That same six-footer also disliked the seat shape; the rider's portion of the seat slopes downward slightly near the mid-seat hump, forcing him forward as he tried to stretch in the saddle. For everyone else the seating position was an ergonomic success. The CX-T's swoopy fairing shields the rider's torso almost completely, and the turn signals protect his hands. Honda shortened the windscreen about an inch to reduce buffeting—the face-level air blast is still mildly annoying. Between the lower portion of the fairing and the jutting cylinders, the Turbo provides plenty of leg protection. Much warm air from the radiator and engine flows back onto the rider; it is welcome on chilly days, unwanted on hot.
Honda controlled vibration well. The Turbo transmits a distinctive, non-objectionable Vee rumble; a light buzz through the handlebars tires the rider's hands after long stints in the saddle, but that's it. Some of the credit for the 650's smoothness must go to the Turbo's new gearing: the 650 turns a leisurely 3876 rpm at 60 mph; the 500T spun a busy 4496 rpm.
Source Cycle Magazine of 1983