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Norton NRV 588
Norton NRV588 - Rotary Revival
Riding The NRV588, A Modern Iteration Of The Wankel Rotary-Powered Norton Racers That Once Ruled British Racing
writer: Alan Cathcart
Alternative ideas for improving sportbike performance usually involve yet another arcane front suspension layout like the Bimota Tesi or BMW's Duolever/ Telelever designs - but rarely has anyone offered an alternative engine. Except for the two-stroke, which became a mainstream concept that eventually has been forced into near extinction by environmental concerns, and not counting the current fascination with renewable fuels, there haven't been any truly innovative concepts in gasoline-powered motorcycle engine design. Well, perhaps except for just one: the Wankel rotary.
The Norton Rotary Reborn
I was able to test each successive year's variant of the Norton rotary racer and found the bikes thrilling to ride, with a good power-to-weight ratio that made them unquestionably fast and with adequate handling. Although the rotary is a dirtier, thirstier design than a conventional four-stroke, it's also lighter and more compact-and potentially more powerful. Just what you need to build a better racebike, as Brian Crighton proved by conceiving the Norton rotary racers that flourished two decades ago. Unfortunately the Nortons withered away after their last race in 1994, thanks to the corporate intrigue that eventually downed the parent company.
But some people never give up, and for 13 years, the 59-year-old Crighton continued to dream of building a Norton rotary racer as light and powerful as he always knew it had the potential to be. Now, with the financial backing of dedicated Norton enthusiast Roy Richards - founder and chairman of Britain's National Motorcycle Museum, where 16 of the 17 Norton factory rotary racers ever made now reside - Crighton's dream has reached reality. The Norton NRV588 is the bike he always wanted to build.
Launched a year ago at Britain's Birmingham Show, and after a season of development held back by the dismal British summer's constant rain, the NRV588 currently produces 165 horsepower at 11,450 rpm from its liquid-cooled twin-rotor engine, yet weighs just 289 pounds with all fluids but fuel. Crighton's ultimate rotary racer offers a power-to-weight ratio comparable to today's factory superbikes, with performance enhanced by current technology that includes a ride-by-wire throttle, fuel injection with a range of usable maps and traction control. "This is the bike I wanted to build for 1995 after we'd beaten the Yamahas and Ducatis plus the RC45 Honda to win the 1994 championship," says Crighton. "I wanted fuel injection for the road bikes to cope with emissions and ride-by-wire throttle to make it easier to ride in the wet via traction control. But they changed the rules to get rid of the Nortons, and anyway the company was fizzling out, so it never got built. But [a British magazine] published an article about my ideas back in August 1994, and when Roy Richards hired me three years ago to restore all his rotary Nortons for the museum, after I'd been working for him for a while I showed him the article. After reading it he said, 'Well, would you like to build it to finish the story off?' He said that he'd finance it personally, and that's how it's come about."
An Old Dog With New Tricks
Another electric motor controlled by the ECU operates the throttle plates, in a copy of the modular ride-by-wire system on Ducati's MotoGP bikes. This has a conventional throttle cable running from the grip to a potentiometer, which translates the action in digital form to the ECU. The ECU then instructs the electric motor to operate the butterflies according to a preprogrammed map that can be altered depending on weather, track conditions, tire wear and so on.
Having ridden both four-cylinder sportbikes fitted with variable-intake systems, I was interested to see how this would work on the rotary engine. I remembered from my several previous Norton rides that it had a broad spread of power but suffered from a lack of low-end torque, especially if tuned for top-end power like the original bikes were. That always made them even more like a two-stroke to ride, and the heavier flywheel required to tame the otherwise explosive powerband also tended to compromise acceleration, only partially rectified by the bike's light weight.
The NRV588 has no such problem. For example, compared with Steve Hislop's TT-winning ABUS Norton, which had a nice midrange but was definitely peaky in terms of power delivery, the new bike feels like it's powered by an extremely potent electric motor. There's a huge range of seamless, linear power from 3000 rpm all the way up to the 11,500-rpm rev limiter. Throttle response is crisp without being abrupt, a welcome trait considering the NRV's high power output and light weight. The 2D LCD dash is hard to read because of the lack of contrast in daylight and the smallish numbers, and the engine is so smooth that you have no sense of feel that it's time to shift. This caused me to bump into the rev limiter often; a bright shift light would help here. The excellent low-end torque meant that driving out of the tight turns could be done in second gear-no need for first gear in the separate six-speed Yamaha OW01 gearbox with belt primary drive. However, there's no power shifter fitted to the race-pattern gearshift, because the engine's relatively heavy flywheel and long gear spacing make it difficult to prevent shock loading while shifting through the lower gears.
But where the variable-intake system in the NRV588 really shows is when you get to 8200 rpm, where maximum torque of 82 ft-lb is delivered, according to Crighton. Here, instead of the midrange flat spot that plagued the older Nortons, the engine keeps pulling hard and continues to accelerate strongly right to the 11,500-rpm limiter. Note that the 165-horsepower number is quoted at 11,450 rpm, which incidentally Crighton says is a conservative figure-he feels 175 horsepower is easily achievable with more development.
The ECU software allows Crighton to dial in a different engine map for wet pavement as well as a different ride-by-wire throttle program and (though it wasn't yet installed for any of my tests) a choice of traction control programs depending on track conditions. With the continuous and overlapping power pulses of the rotary engine making the bike especially prone to wheelspin, this will be a useful feature in the future. It could also allow riders to run a softer rear tire, enhancing traction even more. As it was, even without traction-control programs installed, the NRV's smooth throttle response and linear power made it a confidence-inspiring ride on a wet track-maybe just not as much fun on a dry one.
The bodywork was designed by Harris Performance and painted in colors that recall Norton's classic-era Manx GP singles. The chassis is a Spondon aluminum twin-spar frame based on the '94 Duckhams British Superbike title winner, but because one of Crighton's key objectives in designing the new bike was to maximize the benefits of the rotary engine's compact build, the main spars are 25mm longer to allow for a front-mounted Radtech custom radiator rather than the previous twin side-mounted radiators. This helps reduce the NRV's overall width to just 450mm, more than 50 percent narrower than the old Nortons and not much wider than a 250GP racer. But the rotary engine also has some heat issues caused by the continuous power pulses that can result in exhaust temperatures reaching more than 1000 degrees C. This required a new exhaust system made from costly Inconel alloy, which is more resistant to heat than titanium and is even lighter. Also, to bring cooling air between the rotor housings Crighton borrowed an idea from one of his hobbies. "I fly model aircraft, and they use high-performance duct fans that run at very high speeds and generate lots of airflow," he explains. "There's an electrically driven extractor fan in the duct beneath the seat linked to the ECU, so that as the temperature rises it runs quicker and pulls the heat out of the middle of the engine. The forward ducts on the fairing give a positive effect there, and there's a negative effect at the rear, so you end up with a good cooling airflow. It's the same variable system as the engine's electric water pump, which has no thermostat, just a sensor that monitors engine temperature. As this rises the water pump speeds up, but then it slows down as it cools. It self-regulates so you don't need to tape up the radiator [on colder days]."
There's just a single Öhlins rear shock on the NRV, offset to the right and operating without any link. "A monoshock with linkage is made very progressive, so it only moves a little when the wheel hits a small bump," says Crighton. "This makes it hard to control the damping accurately, as we proved with back-to-back tests on the Roton GP racer, which became Ian Simpson's title-winning Duckhams Superbike. Our system is better because we have more damping control and better consistency, and the braced swingarm is stiff enough we can move the single shock off to the side to help it run cooler without any flex." Rear-wheel travel is only 3.5 inches, while the wheelbase is extended slightly to 56.1 inches with an increased 54/46 percent front-end bias. The fully adjustable 43mm Öhlins fork is set at a 23.7-degree head angle (adjustable via eccentrics) with 102mm of trail.
This Norton was also the first one I rode with Dymag carbon wheels. As a result the pair of chicanes at Mallory Park, where I tested, suddenly became amazingly easy to flick through. However, I found that the Norton likes to take wide, sweeping lines to maximize turn speed rather than stop, turn and accelerate hard, as you might expect with such a slim, light bike wearing wide, 16.5-inch Dunlop slicks. Edge grip was obviously good on my one dry test day, although one handling aspect I didn't care for was the way the NRV liked to understeer under hard acceleration, perhaps because of the engine power compressing the rear shock without a progressive linkage.
But otherwise the Norton tracked straight and true, and I welcomed the exceptional feel of the radially mounted twin 320mm AP front discs and monoblock four-pad calipers. On a bike this fast on such a tight track you need to have absolute faith in your brake package, and the AP brakes provided it, countering the rotary motor's near-total absence of engine braking. The slipper clutch sourced from a Kawasaki parts bin helped keep the Norton stable as it stopped hard, although it was surely aided by the high 2000-rpm idle speed. The gear-change was a little notchy but nothing oppressive.
"It would be nice to run in that kind of racing because of the interest it would create for people who like things that are out of the ordinary," says Crighton. "Whatever the argument is about the capacity, it's a 165-horsepower bike and we're thinking of running it against the 1000cc superbikes producing up to 200 horsepower, so it's a tall order. It'd be incredible if it could be competitive at all, but we're willing to give it a try by using the power-to-weight ratio to our advantage if it's possible. At the moment we've only got the one bike, so if we're going to do any sort of racing we'll need to get a second one built. We do have some spares available, though it is getting a bit difficult with the engine parts now. But we'd like to wave the Norton flag again to show people how a rotary ought to be done right."
Even more to the point, though: How great would a Norton NRV588 street replica be, complete with side ports and fuel injection taking care of emissions (just as it does for Mazda with its RX-8 sports car) and the variable-length intake setup offering superb rideability in a 170-horsepower, 300-pound package?
Source Sport Rider Magazine