John Nutting rides an 80s icon. It’s turbo time!
Suzuki’s XN85 Turbo may not have made a splash when it was launched in 1983, but is a rare and refined creature. John Nutting found not one but two in the deepest south east.
If rarity alone were enough to make a classic with a high and appreciating value, then the Suzuki on which I’m rushing through Kent and Sussex lanes would qualify easily. Like the gorgeous GSX1100 Katana, the XN85 Turbo I’m riding feels long and low, tips into bends agreeably, and powers out with a level of smoothness and refinement the Katanas never had. Wait a moment though, and the turbocharger kicks in at around 6000rpm, giving an extra rush and just enough excitement to make this machine worthy of more attention. We arrive at Wesson’s in Horam and owner Roger Wood tells me he’s had two XN85 Turbos, this second one since 1994, and in those 23 years it’s never given him any trouble. He clearly loves this bike. I mention the refined character to Roger and he reminds me how I described the bigger Katana in an article for Which Bike? many years ago. “You said it was like ‘riding bareback on a shark’,” he said. “The XN85 is more like swimming with a dolphin.” That his XN85 has been solidly reliable belies conventional thinking at the time that turbo-charged motorcycles, which were all the fashion in the early 1980s, were fearsomely complex and therefore prone to all manner of technical problems. Roger’s is particularly special because it’s completely original, right down to the black chromed exhaust system, engine finish, seat cover and plastic body panels, even though it’s been used regularly, although still showing just 22,500 miles on the clock. Because barely more than 1100 were made for worldwide markets for two years from 1983, the XN85 should in theory be more desirable than market prices suggest: good ones barely reach £7000. Perhaps it’s because Suzuki chose to be ultracautious with its specification. Turbo-charged bikes are supposed to be fast and furious aren’t they? Speed record breakers are all fitted with them. Indeed, that’s true of the earliest turbocharged bike I experienced, a Kawasaki Z1000 built in 1978 by Russell Savory on the lines of the Z1-R TC that was offered as a ‘factory approved’ aftermarket kit in the US. Using a massive turbocharger, its power was explosive and it would hairily accelerate to more than 150mph in a flash.
But when the leading manufacturers developed their own turbo-charged machines, they took a more measured approach. For Honda, the CX500 Turbo, launched in 1981 and reaching UK dealers early in 1982, was more a demonstration of what its engineers could achieve by upgrading the modest 500cc liquid-cooled shaft-drive V-twin. With its hefty fairing it was a high-speed tourer rather than a sports bike. During its global launch in Japan it was about as fast as Honda’s DOHC CB750F four. Soon after that Yamaha launched a turbocharged version of the XJ650 four, and again it wasn’t much more potent than the base model. With 90bhp and a big fairing, the XJ650 Turbo was also more touring orientated, with relatively modest acceleration and a top speed at MIRA of 123mph. Only when Honda followed up a year after the CX500 Turbo with a 673cc version boasting peak power of 100bhp, twice as much as the naturally aspirated CX500, did it get interesting. The extra power enabled a top speed of almost 130mph and a quarter mile acceleration of just over 12 seconds. It was against this backdrop that Suzuki launched its own turbo-charged bike. The Hamamatsu factory had been working on its development since 1979, when it was decided to use the four-cylinder GS650 as a base, the theory being that the machine would be less heavy than top of the range 1075cc models. The factory had just launched the GSX1100 and was in the process of designing the Katana range which would make its debut in 1981. The development of the turbocharged 650 was fraught with problems. Using a four-cylinder engine was a good choice because of the smoother exhaust flow than with a twin, but detonation, which occurs when combustion pressures and temperatures rise uncontrollably, wrecked engines. In essence, a turbo-charged engine performs like a larger capacity engine because more air is forced through it by using the exhaust energy to drive a turbine, which in turn is connected to a compressor. As more air flows through the engine, the more power can be produced. But this needs careful control. Ideally, to harness the exhaust’s energy, the turbo-charger should be mounted close to the ports, but this means that on a motorcycle it is far from the inlet ports, leading to a lag in response. A compromise was achieved by better flow in the exhaust pipes that met under the engine, and fed through a single header to the optimised IHI turbo mounted above the five-speed gearbox. From there the compressor drew air from a paper-element filter and a flow meter and fed the ports. Fuel was metered by injectors that were controlled from a simple electronic control unit in the seat fairing. This also controlled the ignition system. Suzuki’s engineers would have probably
“The development of the turbocharged Suzuki 650 was fraught with problems”
liked to have aimed for a 100bhp target to match Honda’s CX650 Turbo, a power figure close to the claimed 111bhp of the GSX1100 Katana and the later 122bhp GSX1100E, its top of the range model in 1983. But the air-cooling that was satisfactory in the engine used in the GS650G Katana presented a challenge as power was increased. So, in addition to switching from shaft to chain final drive, a number of changes were made, starting with larger big-end journals (up from 34mm to 36mm) in the surface treated crankshaft, beefed up small-ends and connecting rods. Internal cooling was improved with oil jets above the main bearings and the con-rods spraying the undersides of the piston crowns. To help dispose of the heat, a seven-row oil cooler was used. The cylinder head was also revised with additional oilways near the exhaust ports and valve gear while ducting fed air over the exhaust cam cover to the spark plug area. Compression ratio was also reduced, to 7.4 to 1: valve timing adjusted and the clutch beefed up. Unchanged were the 62mm bores and a stroke of 55.8mm, giving the engine a swept volume of 673cc. Suzuki’s XN85 Turbo made its debut in November 1981 at the Milan Show where Kawasaki also revealed a prototype turbocharged 750. But Suzuki was quicker off the mark with a press launch early the following year and bikes reaching dealers for the summer of 1983. Power was 85bhp at 9000rpm (hence the XN85 name), a modest claim when the normally aspirated GS750 four made a claimed 83bhp at the time. Strangely, Suzuki offered the
bike at just £2499, the cheapest of the turbos offered by far and more than £1000 less than Honda’s CX650 Turbo. Strange, because the factory limited production and just 40 dealers in the UK were able to sell the XN85. In the US, first to test the XN85 was Cycle magazine in its December 1982 issue, saying: “Suzuki has come up with a fine machine despite its trendiness (turbo-charging) and despite the jump the competition had in developing this new-to-the industry technology. Indeed, in terms of hard-core performance the Suzuki is best of the turbocharged bunch.” But then Cycle, while being the paragon of motorcycle literature, could be effusive when an exclusive ‘first’ test was on offer, as it was with the rotary-engined RE5. In the UK, Motor Cycle Weekly was more circumspect. Tested at MIRA, the XN85 clocked a two-way average top speed of 126.5mph on the 1000-yard timing straight, with a two-way average standing quarter mile time of 12.27 seconds and a terminal speed of 106.9mph. That was much better than the Yamaha XJ650 Turbo’s 123.27mph and quarter mile figures of 12.98s/102.5mph, and closer to Honda CX650 Turbo than the Suzuki’s specification would have suggested. But – and there is always a ‘but’ with turbo-charged bikes – those figures placed the XN85 only among the 1983 750cc fours. Honda’s VF750, Suzuki’s GSX750 and Kawasaki’s GPZ750 were all faster while Yamaha’s XJ750 shaft was about the same. “If that makes you seriously question the whole idea of turbo-charged motorcycles then you’d be in good company,” said Mat Oxley in the MCW test. “Suzuki could probably have got very similar results with a mildly tuned 750.” But such a bike wouldn’t have Turbo in its name – or ‘OBRUT’ as on the snout – and its marketing potential in competing with the other factories would have been limited. Roger Wood’s bike was remarkably unaffected by its 30-plus years. Just as the original bikes were described in the tests, it would sing along gracefully at high speeds and you’d never think you were riding a turbo, as the wind whipped over the bikini fairing and carried the muted exhaust away. Below 70mph it felt more like the 650 it really was, and this was more obvious on twisty A-roads when a bit more top-gear response exiting bends would have been appreciated. To get the best from the engine, it needed to be revving above 6000rpm. Hold onto top and you’d be eventually rewarded with a rush as you passed 80mph, but if you wanted to enjoy the heady rush at lower speeds, drop two gears and the adrenaline feeling was immediately on hand as the turbo’s 10.5 psi came to hand, as indicated by the liquid-crystal display in the centre of the instrument console. And unlike other turbo-charged bikes, there was no real ‘lag’ as such, more an unrelenting increase in silky power, like any highly-tuned four-stroke but without much in the way of mechanical drama. At town speeds, the Suzuki was as mild mannered as you could want, with light controls and easy-going manners.