The World's First Oval Pistons Developed By Honda

The World’s First Oval Pistons Developed By Honda

Sathurshan

January 9, 2020

In 1979 Honda produced the world’s first engine which featured oval pistons with the introduction of the NR500 Grand Prix racer. The oval pistons later found their way in the 1980 NR750 endurance racer and the road going NR.

Honda NR500 Oval Pistons in the Engine Assembly | Photo Credit: HRC

The Honda NR500

Honda’s 70s journey is what led to the creation of the oval pistons. In the 60s Honda had a successful Grand Prix journey before their absence in the early 70s. They decided to return to Grand Prix motorcycle racing in the late 70s. Honda realised during their absence Grand pix have taken over by two-strokes bikes compared to their four-stroke equivalent.

To compete in the Grand Prix Honda preferred working on four-stroke engines. During the development stage, they looked into increasing the number of cylinders. Unfortunately, the Grand Prix rule allowed only a maximum of four cylinders. Honda engineers got back to the drawing board and tried to develop a V8 engine in the form of a four-cylinder engine.

Honda NR500 Engine

The result of this was the NR500 under the NR (New Racing) series, featuring oval pistons with 32 valves and eight con-rods. That meant two con-rods per piston and eight valves per cylinder! On top of that, Honda engineers made all of these fit into a regular four-cylinder engine!

Honda NR500 Assembly

Honda NR500 | Photo Credit: Cycle World

The bike produced 130 bhp at 20,000 rpm, but it did not succeed on the track. The NR500 is one of the radical motorcycles in history that failed. Honda later went ahead with using the NS500 two-stroke machine.

The Honda NR750

Photo Credit: 95 Custom

Honda used the same technology in the NR750 endurance racer later in the 1980s. A few years later in 1992 Honda decided to produce 300 units of the road-going version of the NR750 as the Honda NR. The 750cc road-going NR’s featured elliptical-shaped pistons with long curved sides. The NR500, however, had oval pistons with straight sides.

NR500 Oval Pistons | Photo Credit: Honda Global

NR750 Oval Pistons | Photo Credit: Honda Global

Oval Piston Components

The 750cc 90-degree V-four engine with oval pistons allowed eight valves per cylinder just as the older NR500 engine. The engine generated a vast amount of power as the air/fuel ratio, and the compression in the cylinder increased dramatically compared to an ordinary V-four engine.

NR750 Engine Assembly | Photo Credit: On Road Zone

Honda’s 750cc NR engine | Photo Credit: Honda

The stock road-going 750cc NR was capable of producing 125 bhp at 14,000rpm. When released, the NR cost $50,000. It is considered normal for a rare collectable motorcycle which has one of the most unique engineered and design quirks until today.