The RA302E was an air-cooled, naturally aspirated, 3 liter V8 racing engine that Honda deployed in the 1968 F1 Grand Prix World Championship. It was a challenging and innovative air-cooled engine with a large displacement of 3L, and is still a unique and distinctive engine.

Air-cooled engines have the advantage of being simpler in construction and lighter in weight than water-cooled engines, which circulate liquid coolant inside the engine in dissipate heat. Air-cooled engines can be broadly classified into two types. One is the natural air-cooled engine, which is cooled only by flowing air, and the forced air-cooled engine, which is cooled by air flow driven by a blower. The RA302E was a natural air-cooled engine, the simplest configuration.

Natural air-cooled engines are usually associated with air-cooled motorcycles. However, motorcycle racing engines of that era were small-displacement, natural air-cooled engines ranging from 50cc to 500cc. If larger engines were to be air-cooled, common sense dictated that it needed to be forced-air cooled with a fan to drive the airflow.

In F1 racing history, a forced-air-cooled horizontally opposed 8-cylinder engine won the 1962 season when 1.5-liter engines were mainstream. After that, racing sports cars powered by air-cooled engines ranging from 2 L to 5.4 L supercharged engines appeared, winning world championships, but they were all forced-air-cooled, equipped with oil coolers for the engines’ lubricating oil, and adopted cooling systems that supplemented forced-air cooling with oil cooling.

In this era of air-cooled engines, Honda began research and development of the RA302E as a pure, natural air-cooled engine. This was the development of a big, 3-liter natural air-cooled racing engine, neither forced air-cooled, nor equipped with an oil cooler.

This challenging R&D plan was formulated and implemented by Soichiro Honda, Honda's founding president and the chief executive officer of engineering development and manufacturing. Soichiro had strong views that not only car racing engines but all motorcycles, automobiles, and power products the company mass-produced and sold should be powered by natural air-cooled engines.

On June 29, 1968, Honda announced the RA302, the most advanced Honda F1 car, to the press at Haneda Airport, and immediately began airfreighting it to the Honda F1 team in England. Its engine was the RA302E, a natural air-cooled 120-degree V8 DOHC 4-valve engine with a bore x stroke of 88 mm x 61.4 mm, 2987.5 cc, and maximum output of over 430 HP at 11500 rpm. Later, additional specifications such as a plain bearing crankshaft and titanium metal connecting rods were announced, and photographs of the disassembled engine were also released.

The RA302 which began testing in earnest at the Silverstone Circuit in England had been fitted with an oil cooler on site, and immediately after entering the course demonstrated the agility of a state-of-the-art machine. However, before the car could be set up, the RA302E quickly overheated, making continuous testing impossible.

The RA302 debuted at the French GP on July 7 and qualified, but crashed and burned in an accident early in the race.

Honda hurriedly built a second RA302 and entered it in the Italian GP on September 8, and ran it in the official practice session on September 6, but decided it was too early to participate in the race due to a significant loss of power caused by overheating, and withdrew from Qualifying and the race.

Honda announced its temporary suspension of F1 activities after the 1968 season. Since the Italian GP, neither the RA302E engine nor the RA302 have been seen in public.