In 1992 Honda released two ground-breaking new motorcycles – one went on to change the face of sportsbikes forever, the other went down in history for being the most technologically-challenging and advanced ‘production’ motorcycle ever built. It was certainly quite a year for Honda. The two bikes? The CBR900RR FireBlade and the NR750.
We don’t need to talk about the ‘Blade, because almost everyone knows the impact Tadao Baba’s creation had on the sportsbike world (in fact, you’ll find an article about it here – Ed), so let’s instead focus on the truly staggering NR750 – a bike so advanced for its time the world will never see its kind again. And, in truth, for good reason as this rolling technical showcase should never really have made it to production. The fact it did (albeit in small numbers) is simply down to some corporate showing off, and that’s why it is so special.
The story behind the NR starts way back in the 1970s and was a result of Honda’s determination to do things their own way rather than follow the accepted best path. Some might call this stubbornness but we will say they attempted to challenge convention through clever engineering. How so? Well it all started on the Grand Prix racing grid...
In the late 1970s and early 1980s, GPs were dominated by two-stroke race bikes. Although they were easy to get power out of, strokers were also smelly and noisy – which went against Honda’s vision of the future of two-wheeled transport. They wanted the world to go down the clean and reliable four-stroke route and, in an attempt to prove their point and build a bike which represented the machines they sold, they decided to take on the two-strokes with a four-stroke – the NR500 0X. Things didn’t go well.
The NR500 was not a conventional machine, but then Honda had a reputation for making unconventional and exotic race bikes. This radical machine (NR stood for New Racing) used a four-stroke engine with oval pistons, something that allowed them to squeeze in twice as many valves per cylinder head as a conventional engine and still stay within the technical regulations, which at the time demanded a maximum of 500cc and four-cylinders. Honda’s previous foray into racing had seen some exquisite high revving four-strokes, most notably the six-cylinder 250cc RC166 of the 1960s, but by the 1970s rules had been changed to limit the number of cylinders and gears in an attempt to save costs. Honda backed out of racing when it no longer gave them an opportunity to experiment with new technology. The NR500 was their comeback!
The logic behind the design was simple. More valves equates to more fuel and air into the engine, therefore making more power, and the oval pistons facilitated a staggering eight valves per cylinder. The advantages didn’t stop there, Honda’s R&D department claimed at the time. Due to the shape of the pistons, which are best thought of as being like sardine cans rather than a geometric oval, Honda could actually make the cylinders narrower as the width of the oval piston was 30% smaller than the equivalent pair of round pistons – reducing friction as well as the overall dimensions of the motor. While the theory may have been sound, the reality wasn’t quite as rosy. The racer made its debut at the 1979 British Grand Prix and, after two seasons of poor showings, was withdrawn from racing without scoring a point. Despite the engineering, it was never quite as fast, light or reliable as the four-cylinder two-strokes from Suzuki and Yamaha.
Honda got it right next time and built its championship winning NS500 V3 for 1982. It was a two-stroke, albeit a design which still challenged convention by prioritising light weight and agility over power, before the NSR500 V4 two-strokes dominated the final years of the 500cc Grands Prix. The whole oval piston project was mothballed after the NR500’s last race in 1981, until the early 1990s…
Quite why Honda decided to revive the oval piston motor and build the NR750 is still a bit of a mystery, however most assume it was simply a case of the company wanting to showcase its engineering prowess and build a bike that no one else could ever do. In fact, the NR’s sales brochure proudly states ‘There is no limit to the places a dream can carry you. All it takes is the determination to get there’ on its cover, hinting at the NR being a bit of corporate showing off. So when, in 1990, the travelling marshals at the Suzuka 8-Hour race rode around the track on the NR750, the world was very surprised indeed. And, it has to be said, also incredibly impressed – even more so when the NR750 was launched in 1992 and its full spec revealed.
Honda only made 322 examples of the NR750 (20 of which were the 100bhp variant for Japanese and French markets) and when you delve into their spec you can see why. Costing a truly terrifying £38,000, which is £82,000 in today’s money, the NR750 was built with a remarkable attention to detail. Starting with its motor, the 747cc 90-degree V4 engine features oval pistons with eight valves per cylinder, four intake and four exhaust. Each piston not only has to have oval piston rings (a feat of engineering in itself), they also run two titanium conrods while the head has two spark plugs, twin fuel injectors and even two intake and two exhaust ports, per cylinder. Technically it is a V4 motor, but essentially what Honda built was more like a V8! The complexity is mind-boggling and, believe it or not, Honda even managed to get it revving to 15,000rpm thanks to gear driven cams. Add to this an 8-into-4-into-1-into-2 exhaust, which exits under the seat (more on this later...), a cassette gearbox and unique U-Vent cooling system with dual-element flat and curved radiators working in series and you get an understanding why the NR commanded such a high price tag. And it didn’t stop there, not by a long shot.
Much like the ‘Blade, the NR used computer modelling to create a triple-box cross-section aluminium beam frame that incorporated the V4 motor as a fully stressed member and then added a single sided swingarm, inverted forks (the Blade didn’t have these) and four-piston brake calipers with NR branding. It even ran trick wheels, made from magnesium alloy for lightness, with the front a 16” and the rear 17”.
And then there were the final touches that really cemented the NR’s status as the most exotic bike you could buy. The bodywork was futuristic and the NR’s clocks sat in a carbon fibre panel, which is cool, but the instruments themselves have a ‘floating LCD’ speedo display. Using an internal mirror, the display is reflected up, creating a sense of depth that means your eyes don’t have to adjust to read it. And then there was the final touches of a nickel silver ignition key in the shape of an oval piston with an NR-branded carbon inlay and the bike’s beautiful red paint scheme (which is a nightmare to match) on carbon bodywork, with an iridium-coated screen and those underseat pipes. Yes, underseat pipes, two years before the Ducati 916 and as the Italian bike’s designer, Massimo Tamburini, later acknowledged, the NR750 gave him the inspiration for the 916’s rear end. The NR750 may be unknown or forgotten about for many motorcyclists, but its impact on 1990s motorcycle design and engineering should not be underestimated.
In 1992 most viewed the NR750 as a bit of a folly, mainly as it only made a fairly low power figure of 125bhp with 48.7ftlb of torque, which wasn’t much better than the FireBlade. True, Grand Prix champion Loris Capirossi managed to hit 200mph on (a modified) one during a Honda PR event in Italy, but the NR was far from a superbike and nowhere near as light or agile as a ‘Blade. And obviously, its price tag was quite a hinderance to sales! While a few rich bike nuts and collectors did buy them, much like the subsequent RC213V-S which followed over two decades later, it was a predictably slow seller. Did Honda care? Not at all, the NR750 had served its purpose in life and when it comes to corporate posturing, it is hard to argue with the NR750 as a machine that cemented Honda’s reputation as the leading two-wheeled engineering company on the planet. It is a truly astounding engineering feat.
Nowadays the NR750, which will set you back around £100,000 if you fancy one, remains a very special machine, being less of a classic motorbike and more a rolling work of art. Although not particularly outstanding to ride in terms of its performance or handling, and with truly terrifying costs should the V4 engine develop an issue, it is an incredible motorcycle in terms of its engineering and in years to come will still be unique. No one has since dared to replicate Honda’s oval-piston engine design and it is highly unlikely they ever will – for a very good reason!
Specs:
Engine: 747cc, liquid-cooled, 32v, DOHC, 90-degree V-four
Power: 125bhp @ 14,000rpm
Torque: 48.7Nm @ 11,000rpm
Seat height: 785mm
Weight: 223kg (dry)
