Turbo Wars: Kawasaki ZX750E1 vs. Yamaha XJ650LJ

Turbo Wars
By Doug Mitchel
July/August 2008
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Kawasaki ZX750E1
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In life we’re faced with choices: republican or democrat, blond or brunette, paper or plastic? Shopping for a new motorcycle in the early 1980s, you also had to choose between normally aspirated or turbo models.

As the 1980s picked up steam, each of Japan’s Big Four (Honda, Kawasaki, Suzuki and Yamaha) offered up at least one turbocharged model based on a standard offering. The train of thought was simple: Combine a 650cc or 750cc engine with the power boost of a turbo and wham! — big power. For some shoppers, just the allure of turbo technology was reason enough to buy. And while each manufacturer (excepting Honda) used the same basic formula (inline-four engine + turbo = new model), each company’s creation was a bit different.

To get an idea of what the Turbo Wars netted, we pitted Kawasaki’s ZX750E1 (also commonly referred to as the GPz Turbo) against Yamaha’s XJ650LJ Seca. Kawasaki had delivered — albeit unofficially — the Z1-RTC in the latter part of the 1970s, but the ZX750 turbo was a true production unit and therefore better suited for this standoff. Both of the chosen combatants were based on existing offerings, but in keeping with their higher output mills were better dressed and equipped.

Getting to know them 

Following the debut of the original Z-1 in 1973, Kawasaki positioned itself as a dominant player in the high-performance market. Engines from the Z and later KZ models routinely found their way into championship-winning drag bikes and were widely considered to be among the strongest mills available. With other manufacturers exploring turbo power, adding a turbocharger was a logical step and created a new high-horse monster for Kawasaki.

Yamaha’s history was not carved from the same stone as Kawasaki’s, but the company had a number of diverse machines to its credit. Yamaha’s legendary 2-strokes and the XS650 twin and XS1100 inline-four earned high honors among riders on the street, and Kenny Roberts took the Yamaha banner to the winner’s circle repeatedly during the 1970s.

On paper, the ZX and XJ share a number of similar traits. Beneath their futuristic body panels they both have a tubular steel chassis carrying an inline-four engine. The similarities continue: The ZX wheelbase is 58.7 inches; the XJ measures 57.1 inches. Full of fuel and fluids the ZX weighs 556 pounds; the XJ 567 pounds. Seat heights are almost identical, falling within 0.3 inches of each other with 30.7 inches for the ZX and 31 inches for the XJ.

But even in their commonality, they are very different machines. The ZX mill displaces 738cc; the XJ 653cc. That difference in displacement gives the Kawasaki a 10hp edge over the Yamaha, with a claimed 95hp at 9,000rpm. This bump in power shows up at the drag strip, with the ZX trumping the XJ by more than a second in the quarter mile at just over 11 seconds against the XJ’s 12.68-second time.

A major contrast between the two bikes is their method of fuel delivery. The XJ uses a bank of four Mikuni 30mm carbs while the ZX features electronically-controlled fuel injection. This provides the ZX with enhanced go-juice delivery and seamless response when the throttle is yanked open.

A power-robbing feature of the XJ may be the final shaft drive, whereas the ZX uses a chain, allowing more of the engine’s power to reach the rear tire. This choice of hardware may also tell us a bit more about the intentions of the XJ as a sport-touring mount versus a balls-out performance ride. The ZX has a pair of discs up front and one at the back, where the XJ relies on dual-disc front and a drum rear.

On the road 

To get these great bikes out on the road, we called in two experienced riders for their seat of the pants input. In the yellow helmet is Sandy Callas. With more than 35 years of riding experience under his lid, he brings a wealth of knowledge to the table, and having owned a bevy of vintage and modern Japanese machines, he’s a good contrast to silver-helmeted Ken Rottmann, who takes the other side of the ring. Ken matches Sandy for riding time, but his interests lean toward the British end of the pool.

Getting familiar with the bikes, both riders found the Kawasaki to be a far more aggressive machine in every way, from seating position to throttle response. Sandy has owned numerous GPz models through the years, and he found the turbo Kawi similar to the bikes he’s owned, with the obvious difference of more power. Ken mentioned that the turn-signal cancelling on the Kawasaki is cumbersome and a bit distracting while in traffic. Maybe it’s the performance aspect of the ZX’s design that kept it from being as comfortable, too, but Ken felt cramped in the seat and thought a shorter rider might feel more at home. Sandy’s overall impression of the Kawi was about the same, labeling it a sharper-edged machine than the Yamaha. Ken also disliked the top-of-the-tank location for the Kawi’s gauges, saying they were hard to read, forcing the rider to take his eyes off the road. Both riders thought the Kawi’s windshield was too short, providing far less protection than the Yamaha.

Back in the day, the motorcycling press had lots of praise for the Kawasaki. "The Kawasaki T-bike is … the quickest and fastest turbo by a substantial margin. ... Granted, the other turbos are 650s and the Kawasaki is a 750; nevertheless, when you’re talking horsepower, the numbers win," said Cycle magazine in its November 1983 issue. "No normally-aspirated 750 — and few normally-aspirated anythings — can best the Kawasaki’s turbo-pressurized acceleration, its headlong rush, its willingness to leap from 60 to 120 mph in what seems like less time than it takes to read this line," said Cycle World in March of 1984.

The Yamaha, on the other hand, is a different beast. Ken thought the XJ felt heavier than it was, but also liked the XJ’s more comfortable riding posture. Sandy also called the XJ a "softer" machine, but again admired its comfort. Both liked the wind protection of the XJ, and both riders suggested it was likely the better sport-touring mount of the pair, capable of providing comfort and performance over long distances. Having once owned this exact Seca turbo, I can attest to the bike’s overall ease of use and comfort when ridden on long expanses of macadam.

Although the Seca was considered docile when out of the boost range, things get very interesting when you breach the 6,500rpm notch on the tach. The rush at that point is immediate and urgent, quickly pinning the ridiculous 85mph speedometer. The Kawi is similarly explosive when it comes on boost, and the press seemed surprised by the bike. Before the Kawi, the Honda CX500 Turbo was the only Turbo bike out there, and most testers found the Seca to be a much better overall package. "The Turbo Seca transforms itself from motorcycle to superbike and back again with ease, and the transformation is simply controlled by the right wrist. No phone booths, full moons or other props are needed," said Cycle World in its June 1982 issue.

Who wins? 

Terrific mirrors allowing riders to actually see behind themselves combined with easy-to-use turn-signal cancelling add up to more votes in favor of the Seca. Styling-wise, the Seca uses sharply creased panels and contrasting graphics for a far more space-age look that some think has aged poorly. The Kawasaki’s panels all flow as one, leading the eyes from the nose to the tail in a seamless fashion. The red and black motif accented by silver panels adds mystique to the overall appearance, and most think it’s a generally more handsome machine.

Looking them over, it seems that both of these variations on the turbo theme filled a different niche. The boosted power of the middleweight engines is a welcome feature on both, but the way they use and handle their newfound power is what sets them apart.

Ultimately, the insurance industry made it all but impossible for anyone to afford the required coverage on these puffer bikes, leading to their premature demise. The engineering, design and function was truly cutting edge for the day, and that has put them high on collectors’ lists as the market has finally embraced Japanese bikes as something worthy of attention. Not every model from Japan is loved or coveted, but the turbos are blowing in strong — just like they perform. MC 


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