History of the modern 400cc Superbike

Generally underrated by western markets, smaller high performance bikes (250cc and 400cc) were hugely popular in the domestic Japanese market, mainly as a result of strict licensing laws, making owning bigger bikes prohibitive. Bikes bigger than 400cc were build for export, and usually had 400ccand 250cc versions developed for the local market. The four-stroke 400cc race-replica market was fiercely contested for about a decade from the early 80’s to the early 90’s, with intense development and competition involving all of the Japanese motorcycle manufacturers. The intense competition spread to such series as the production-based SP and the TT-F3 races. The innovative technologies that debut on these 400cc bikes indicated the importance of this class in the Japanese market during this time. By the late nineties Japanese laws were relaxed, and the focus on the tense development of these models subsided.

A few of these models were officially imported into some western markets during their time of production, and was very expensive. (An officially imported VFR400 into the UK in 1989 was as expensive as the top of the range CBR1000F, almost 7500 pounds.) But moderately used models (another anomality of the Japanese market, that make taxes on older bikes also too expensive to keep on the road) began to be imported from Japan by independent specialists, and soon they represented good value for money.

Honda

Designed mainly for the tastes of the European market and launched to the public by the end of 1974, the Honda CB400 four was the first high performance 400cc bike with its multi-cylinder engine, sporty styling, low handlebars and curvy 4-into-1 exhaust system. Up until then, the 400cc market produced mainly parallel-twin engined bikes, like the Suzuki GS400 (1977 – 81), the Honda CB400 twin (1978 – 86), the Kawasaki Z400 twin (1977 – 83) and Yamaha XS400 of 1978.

The CB400 Four was styled after the legendary CB750, generally regarded as the first superbike, and also to take advantage of the café-racer boom. It was based on the traditionally styled CB350 Four with its single-overhead cam, air-cooled and two-valves-per-cylinder. For the CB400 the displacement was increased to 408cc and it gained a 6-speed transmission.

In 1976, Japan introduced a three-tiered motorcycle license system; a license for small bikes to 125cc, medium bikes to 400cc, and a third one with no displacement limit.

Honda responded by releasing a second CB400 Four, with a 398cc displacement, but only one horsepower less. Both the 398 and 408 cc models were available in two types; one with low handlebars, and a second one with higher handlebars suited to the more traditional rider. The 398cc model was distinguished from the bigger one by its black side covers, and as the only four-cylinder models in the 400cc class, both bikes was very popular. Production ended in 1976.

Honda’s V-four programme began in 1982 with the VF750F and VF400F; the smaller bike evolved in lockstep with the bigger one over the following two decades. It featured a bikini-fairing with a tubular steel frame holding a 90 degree V-four engine with chain-driven cams. The following year the bike gained a full fairing.

Along with the launch of the VFR750F in 1986, Honda also unveiled the first VFR400R (NC21) with a twin-spar aluminum frame. Following reliability issues with the cams of its V-four engines, the bikes now sported gear-driven cams that needed no adjustment, and a 180 degree crankshaft. The following year it became the NC24 with the pro-arm, single-sided swing-arm.

The Honda VFR400R NC30 was unveiled in 1989, a street version of the RVF400, a racing bike that competed successfully in the Isle of Man Tourist Trophy and was nearly unbeatable in the All-Japan F3 championship. The streetbike looked like the evocative VFR750R RC30 racer, itself the street version of the RVF750 endurance racer. The unique V-four engine now employed a direct rocker-arm design that in which the camshaft is positioned on the valve axis, greatly reducing friction loss, while the crank was now a 360 degree design. The chassis was a closed-box twin-spar aluminum frame stiff enough to hold a 750cc engine. It had 41mm diameter forks, floating disk brakes, and the distinctive aluminum single-sided swing-arm. In racing trim, the bike produced 66hp and weighed 142kg.

The NC30 was also discontinued in 1993, replaced by the RVF400 NC35 in 1994; a miniature version in appearance of the RC45 complete with inverted forks, but with the lower horse power limit. It was discontinued in 1997.

Kawasaki

Kawasaki revived the multi-cylinder 400cc market with the Z400FX in 1979, an air-cooled two-valve-per cylinder model which was followed by the Z400GP in 1982 and the GPZ400F in 1983.

In 1985 Kawasaki produced its first 16-valve liquid-cooled 400cc model, the GPZ400R. The bike featured the same type of aluminum double-cradle “cross frame”, with the engine enclosed by tubes just like the GPZ600R. While its competitors were undisguised race-replicas, the GPZ was a practical bike offering comfort with its low seat and excellent wind protection. Its long wheelbase gave it stable and easy handling. It was a unique offering, and hugely popular. It was also not slow in spite of its touring orientation; with a lot of low to midrange torque, and power increased way beyond 8000rpm until way beyond its quoted peak at 12000rpm. This set the template for its replacement, the ZZ-R400 in 1990.

Kawasaki launched the GPX400, a sportier version of the GPZ, followed by the ZX-4 in 1988.

The Kawasaki ZX-4 was replaced by the ZXR400 in 1989, which ran alongside the ZZ-R400.

Suzuki

Suzuki released its first multi-cylinder 400cc in April 1981, and it also was the first ever 400cc streetbike with four-valves-per-cylinder – the GSX400F, styled after the groundbreaking Katana of the time. The 4-valve Honda CBX400F followed six months later.

Up until then all 400cc multi-cylinder bikes had two-valves-per-cylinder and was air-cooled.

The GSX400FZ Impulse was built for the Japanese home-market only in 1982, featuring a distinctive frame design, and oil-cooler and an additional three horse-power. It was again released in updated form only for one year in 1986.

In March 1983 Suzuki released the GSX400FW to replace the 400F, with a liquid-cooled engine mounted in a square-tube frame. It was quoted at 52hp and could be revved to 11500rpm. Yoshimura entered a tuned version with a special frame in the Japanese TT-F3 race. The FW came out one month ahead the Yamaha XJ400Z, which was only the second 400cc bike to get a liquid-cooled engine. The FW was discontinued the following year, gaining four extra horse-power.

In March 1984 came the GSX-R400, built with Suzuki’s multi-rib Aluminum Box frame - created by Etsuo Yakouchi, director of Suzuki’s racing activities. The GSX-R400 was inspired by the GS1000R XR41 endurance racer, borrowing much of its technology and appearance, and also took some lessons from Yoshimura’s FW-based TT-F3 racer. It was only the second production bike to get a lightweight, stiff aluminum frame, after Suzuki’s RG250 Gamma. The forks had the fashionable anti-dive system of the time, and the rear suspension sported a full-floating kit that could be adjusted to soft for comfort in everyday riding or hard for sport riding. Yakouchi used the GSX-R400 as template for creating the trendsetting GSX-R750, a year later, as is evidence in the similar frame design.

The GSX-R’s engine was based on the FW, but with major revisions, such as 10mm plugs that made room for much larger intake and exhaust valves. This boosted power output to 59hp at 11000rpm, which tied it with Yamaha’s FZ400 of the same time. The maximum power was the limit set for a 400cc bike by the Japanese government. The engine also featured Suzuki’s just-developed “twin-swirl combustion chamber” for greater combustion efficiency. However, at 152kg was far lighter than the FZ400 and Honda CBR400R, giving it a better power-to-weight ratio than even the RG250 Gamma 2-stroke racer, making it the fastest in its class. In racing trim it was even more astonishing, with 67hp and 134kg.

The GSX-R was sold alongside the sports-touring GSX400F (1988-1989) and RF400 (1993-1999) for the years indicated.

Yamaha

The Yamaha FZ400R of 1984 was created by dropping the new four-valve engine from the XJ400Z into a double-cradle steel frame with a wide-loop tank rail, and styling based on the F3 racers.

Yamaha released the FZR400 in 1986 with concepts from its Genesis featuring in the model like an engine with a forward slant of 45 degrees, just like the FZ750 of the previous year. This allowed a low centre of gravity and made it possible to set the carburetors on top of the engine, while incorporating straight intake tracts for improved combustion efficiency. The aluminum Deltabox frame was adopted from the TZR250, a year earlier than its appearance on the FZR750. It featured low-profile radial tyres – a first for a production bike.

Where to now?

In many countries, including South Africa, 400cc grey models still trickle in, and will continue to do so for a handful of years, but the 400 era has drawn to a close. Suzuki produced an SV400 version of the previous carbureted version its popular 650, and is perhaps the most modern – or rather recent - 400 road bike at the moment, at least as far as I know. It is unlikely to see more 400 versions of bigger bikes, like a Yamaha R4 or a new Kawasaki ZX-4R, but I will be happy to be wrong.

The laws might have changed in Japan, but their affinity with the 400cc class remain. Retro café-racer bikes like the single-cylinder Honda CB400SS have been taking off in Japan in recent years, and again, is build for their local market only. It is only fair to assume that they will land up in western countries soon.

With the demise of the 400cc and 250cc superbikes, as well as the 250cc two-stroke and 125cc two-stroke (not counting the expensive Cagiva, Aprilia and Derbi models), a chapter in motorcycling history is closed.

(Old) Japanese laws on power and speed restriction:

Prior to 1993 the maximum horsepower were the following:
250cc class: 45hp
400cc class: 59 hp
750cc class: 77 hp
over 750cc: not allowed

The new limits for the models built in 1993 and after, were:
250cc class: 40hp
400cc class: 53 hp
750cc class: 77 hp
over 750cc: allowed, but restricted to 100 hp.

All motorcycles for the Japanese home market is restricted to 112mph. Bikes with more powerful engines and unrestricted topspeeds are made for export only. However, a Japanese person is allowed to import an unrestricted bike from another country for private use.

Sources:
Used Motorcycle Guide, UK
Bike UK, August 2001, “GSX-R: The cult”
www.suzukicycles.org
The Ultimate Motorcycle Encyclopedia, Roland Brown and Mac McDonald, 2002, New York
Tourist Trophy Playstation Game

Below: The Honda CB400SS; the new generation of grey-imports 400cc from Japan?