On September 12, 1983, Honda had a secret test on a particular bike at the Suzuka Circuit. It happened just a week after Honda won the first premier class riders' title of the FIM Road Racing World Championship at the San Marino GP. The test was held with a prohibited entry to the paddock by anyone other than those involved because the bike was a new GP500 road racer equipped with a newly developed V-type 4-cylinder engine.

Honda resumed participating in the WGP 500cc class in August 1979. At first, they competed with the NR500, which had a 4-stroke engine with oval pistons. However, they started using the NS500 with a 2-stroke engine from the opening race of the 1982 season.

According to the regulations, the GP500 road racer could only have a maximum of four cylinders. However, Honda daringly chose a 3-cylinder engine for the NS500 to compete on par with rival racers with 4-cylinder engines. In addition, Honda made the new machine lighter and more compact, improving speed in a straight line and maneuverability due to low air resistance. In 1983, the second year after its introduction, Freddie Spencer won the World Championship with this 3-cylinder engine. The aim of HRC was proven to be correct.

That said, the 3-cylinder engine, being inevitably disadvantageous in terms of power, would reach its limit sooner or later. It was none other than HRC who recognized the situation. Immediately after the 1982 season, when the NS500 finished its first year of competition, developing a 4-cylinder engine started in earnest.

After HRC completed the work to update the NS500 for the 1983 season, they began designing a single-cylinder prototype engine with a displacement of 125cc, equivalent to one cylinder of a 500cc 4-cylinder engine. This prototype was the first step in developing the NSR500 series, equipped with a 2-stroke V4 engine that would continue running in the WGP 500cc class until 2002. The experimental 125cc engine had a 54.0mm bore and a 54.5mm stroke with a crankcase reed valve intake.

In April 1983, design work began on a V4 engine with the same bore stroke and intake system as the single-cylinder prototype. Honda would adopt this specification in all V4 engines of the NSR500 that entered into actual races. They completed preliminary work on June 30. On the same day, the project for the first generation NSR500 to be introduced in the 1984 season officially started with its development code, NV0A.

If you are to adopt a new engine, you should also update the body design. However, there was a high-ranking person who warned the engineers. "Just being new is not enough," said Takeo Fukui, who was in charge of development and racing operations at HRC back in those days. Masamichi Komori, who played a role as NV0A's Large Project Leader (LPL), revealed in a 2011 interview that Mr. Fukui had given them powerful instructions, saying, "It's no good just putting four cylinders on it. Invent something new and special."

Honda first worked on the NR500, aiming to beat the 2-stroke racers with a 4-stroke engine of the same displacement, and then created the NS500, which was a 2-stroke but with a unique 3-cylinder engine with which Honda finally won the world title. There was a radical mindset within the newly established HRC that the new 4-cylinder engine had to be accompanied by something other than an orthodox chassis design.

The result was a tricky layout that placed the fuel tank under the engine. However, this was not a forced idea. It emerged spontaneously during repeated deliberations by the engineers.

The maximum fuel tank capacity allowed by the GP500 road racer regulations at the time was 32 liters. If you fill it up, the fuel alone will weigh 24kg, approximately 20% of the lower limit for the dry weight, 115kg (without fuel, cooling water, etc.) As the position of such a heavy object is moved from above the engine to below it, there is no way that it will have a negligible effect on the motorcycle's maneuverability.

This upside-down layout aimed to lower the center of gravity. Why did HRC engineers pursue a lower center of gravity so much at the time? Komori, mentioned earlier, explained, "This is to prevent wheelies and rear wheel spinning."

Komori and his team were having a lot of trouble with the previous NS500 because its front was easily lifted during acceleration. That's what happened with the 3-cylinder engine, so it's obvious what will happen if you put even more power without taking any counter-measures. At that time, HRC had still not yet refined the output characteristics of the 2-stroke engine and had high expectations for the chassis to suppress front lift during acceleration. What was dominant among them was the idea that the center of gravity should be lower and closer to the front.

Instead of reviewing the machine's dimensions, how about dramatically moving the fuel tank to lower the center of gravity? It might be Honda's response to instructions to "invent something new and special." With this in mind, Fukui gave the green light to adopt an ambitious body layout relatively quickly.