Honda NR750 (RC40)
With Ian Falloon
Honda has a long history of creating some of the most exotic motorcycles ever to grace the planet, but many of these have been for racing only and not available to the general public, even the most well-heeled. But in 1992 that all changed with the release of the Honda NR750, the first, and only opportunity for customers to experience Hondas’ achievement with oval-piston technology.
Unfortunately, by the time the NR750R was released oval piston cylinders were outlawed by the FIM so the NR750R was always going to be a novelty. Ultimately, instead of creating a race replica, Honda marketed the NR750 as an extraordinarily expensive collector’s bike.
Although based on the 1987 endurance racing NR750, the production engine differed in that it was a 90-degree V-four (like the RC30) rather than the 85 degrees of the racer.
Ostensibly a V8 with four pairs of siamesed cylinders to bypass FIM regulations banning V8s, the pistons were 101.2 x 50.6 mm, and the stroke 42 mm, giving 747.7 cc.
As the bore is not conventional, it is stated as 101.2 x 50.6 mm, which if calculated as a conventional round piston would come at 75.3 mm
Inside the motor was a myriad of special components, from the eight titanium con-rods to the nickel-plated and Teflon-coated pistons. Each piston ring required 27 machining operations, the spark plugs were 8 mm, and the eight 30 mm chokes featured a single fuel injector.
A departure for Honda was the incorporation of PGM-F1 electronic fuel injection. Fully mapped, with seven sensors and a 16-bit CPU, this also included a self-diagnostic function.
Also included in the exotic specification were gear-driven double overhead camshafts, eight valves per cylinder, set at an included angle of 29 degrees, and with an 11.7:1 compression ratio and 8-into-4-into-2-into-1-into-2 stainless steel exhaust system the power was 125 horsepower at a very moderate 14,000rpm.
The power could easily have been increased to over 140 horsepower but Honda decided to restrict the output to improve longevity and rideability, figuring rider comfort and control more important than absolute racetrack prowess.
The NR750R chassis was more conventional than the motor, with the usual aluminium beam frame, and single-sided swingarm. The front fork was a 45mm upside down Showa, and the specially designed wheels 16 and 17-inch. Honda even had GP partner Michelin develop specific radial tyres, in particular a 130/70ZR 16-inch front claimed to offer the same rolling circumference as a normal 17-inch front.
Even by modern standards the chassis specification is up to the mark, the Showa suspension delivering compliance and feedback comparable to units a decade in the future, while the 310 mm floating front discs with four-piston calipers provided more than enough stopping power for the hefty NR750.
Weighing 222.5 kg, and rolling on a 1,435 mm wheelbase, the NR750 was never going to be a svelte sportster. But it was crafted with the most incredible attention to detail and built out of the highest quality materials.
The carbon-fibre body panels were individually hand-made in numbered sets, flaps hid the side stand when it folded, and the seat finished in crepe urethane. Even the bespoke nickel silver and carbon-fibre ignition key emphasised the oval piston concept.
No detail was overlooked and the production was extremely limited, to only 322 examples. 220 were built in 1992 and a further 102 in 1993, each requiring a 25 percent deposit and built to order on a first come, first served basis and they were only officially sold in Japan and Europe.
While the NR750 wasn’t the high-performance superbike everyone expected from Honda, in many ways it was the ultimate real world high tech motorcycle. More comfortable than a superbike, it also provided superb handling and braking, along with sensational styling.
Even at the outrageous and astronomical price tag, purchasing an NR was more than simply buying an expensive piece of exotica. With the NR you bought into a 13-year oval piston legacy, and a piece of motorised history. More than twenty years on the NR750’s appeal hasn’t faded, and if the prices of used examples are anything to go by it has become even more revered for the intriguing and fascinating engine that powers it.
Five things about the NR750 and oval-piston Hondas
- The NR750’s engine wasn’t the only ground-breaking feature. It was the first Japanese sportsbike to feature fully-mapped EFI, and the first from any country to use an upside-down front fork, carbon-fibre bodywork, side-mounted radiators, and under seat exhausts. Another first was a digital speedometer.
- The first oval piston Honda was the ill-fated NR500. Intended to match the current two-stroke 500cc Grand Prix Yamahas and Suzukis, this made its first appearance at Silverstone in August 1979 but both examples failed to qualify.
- After throwing everything at developing the NR500, the improved 2X appeared for 1982. Revving to 22,000 rpm, rising star Freddie Spencer managed to beat world champion Kenny Roberts in a heat race for the Laguna Seca 200.
- Undeterred by the NR500’s failure Honda turned their attention to a 750cc oval-piston endurance racer. Entered in the 1987 Le Mans 24-hour race Australia’s own Malcolm Campbell qualified second fastest. In the race the NR750 lasted only three hours, until a big-end bolt loosened, blocking an oil way and seizing a piston. The NR750 subsequently made an appearance in the 1987 Swann series. Now producing 160 horsepower, Campbell won one race and finished the series third overall.
- As the NR750 couldn’t be homologated for racing, Honda prepared a 180 kg, 155 horsepower record breaking machine for Loris Capirossi to ride at the Nardo test track in southern Italy. In August 1992, Capirossi set new flying mile, flying kilometre and standing start mile and 10-kilometre records, with a fastest speed of 299.825 km/h.
Honda NR750 Specifications
- Engine Capacity – 747.7 cc
- Engine Lay-out – 90-degree V-four
- Bore – 101.2 x 50.6 mm (Equivalent to 75.3 mm if calculated as a circle)
- Stroke – 42 mm
- Compression Ratio – 11.7:1
- Valves – Cam, gar-driven DOHC, eight-valves per cylinder
- Engine weight – 80.5 kg
- Induction – PGM FI, 8 x 30 mm throttle bodies
- Ignition – Computer-controlled digital transistorised with electronic advance
- Clutch – Wet, multi-plate, hydraulic
- Gearbox – Six speed
- Total Oil Capacity – 4.7 litres
- Oil Capacity at oil/filter change – 3.9 litres
- Oil Type – 10W-40
- Frame – Triple-square section twin-tube
- Caster Angle – 24deg 30′
- Trail – 88 mm
- Front Suspension – USD telescopic forks, 120mm travel
- Rear Suspension – Vertically-asymmetric Pro-Arm swing arm with Pro-Link, 120 mm travel, nitrogen charged piggyback shock
- Rims – Magnesium Alloy, 16×3.5″ (F), 17 x 5.5″ (R)
- Tyres – 130/70-16 (F), 180/55-17 (R)
- Front Brakes – Dual 310 mm discs, four-piston calipers
- Rear Brake – 220 mm ventilated disc, dual-piston caliper
- Fuel Tank Capacity – 17 litres
- L x W x H – 2150 x 700 x 1190 mm
- Wheelbase – 1435 mm
- Seat Height – 785 mm
- Ground Clearance – 130 mm
- Dry Weight – 223 kg
- Kerb/Wet Weight – 244 kg
