Honda (New Racing) V-four motorcycle engine series started in 1979 with the 500cc NR500 Grand Prix racer that used oval pistons.This was followed during the 1980s by a 750cc endurance racer version known as the NR750. The oval piston concept allowed for eight valves per cylinder which generated more power due to the increased air/fuel mixture throughput and compression. In 1992 Honda produced around 300 street versions of a 750cc model, the NR (often mistakenly referred to as the NR750), with a 90-degree V angle. Whereas the NR500 had used an oval piston with straight sides, the road going NR750 used an elliptical piston with curved long sides. The bike became the most expensive production bike at the time when it was selling for $50,000 and with the rarity, nowadays they rarely change hands.
What's most special about the NR750 is its engine. The NR is clever in many respects, but the it is the engine that sets it apart from any other motorcycle. This liquid-cooled V4 motor uses oval pistons, no less than eight valves per cylinder and features a highly sophisticated fuel-injection system. A 32-valve fuel-injected V4 750 is an astonishing feat of engineering, and one which allows Honda to produce a lot of power from a relatively small package.
Each of the two cylinder banks has double overhead cams. Each piston (they are actually oblong shaped, but with rounded-off corners, rather than purely oval) has two con-rods, two spark-plugs and eight valves. Why all this high-technology? Engines using lots of valves, all opening and closing quickly, can rev higher than ones with fewer valves. With a rev limit of 15,000rpm and an advanced fuel-injection system, the NR750 produces an impressive 125bhp (although pre-production prototypes were capable of 140bhp and the racing bike on which the NR is based was making more than 160bhp). But there's more to the NR750 than oval-piston technology.
The aluminium-alloy chassis is a work of art, combining strength and rigidity with lightness, and the NR's suspension is the best money can buy. At the front the NR features massive inverted Showa i forks and at the back it uses Honda's fiendishly [clever single-sided swingarm developed for fast wheel changes in endurance racing. But most breath-taking of all is the body-work, i an impressive mixture of carbon-fibre and fibreglass that costs more than the total price of any other mass-production motorcycle. Even the NR's windscreen is titanium-coated and costs more than most people earn in a month.
The styling of the bodywork is sleek and seductive, the lines beautiful and the finish higher quality than anything seen before from a 'mass-produced' motorcycle. As far as performance goes, the NR is good rather than exceptional. There are plenty of other motorbikes that will accelerate faster and reach a higher top speed, but the NR750 is one of the best handling bikes on the road, capable of going from 0-60mph in under four seconds and reaching a top speed of 160mph.