How Honda's Four-Cylinder Gamble Created the Modern Superbike

British Twin Cylinder Dominance

Four-cylinder engines may be the obvious motor of choice for large-capacity, performance-oriented motorcycles today, but this wasn't always the case. It was British twins that dominated the world of high-speed motorcycles and the motorcycle industry as a whole, through most of the 20th century. Mainstream manufacturers like BSA, Triumph, and Norton ruled the mass market with their ubiquitous parallel twins, while more prestigious marques like Brough Superior and Vincent built highly exclusive V-twin-powered machines that were the fastest production bikes of their time.

Enter the Japanese

As the British motorcycle industry reached its peak in the late 1950s and early 1960s, Japanese bike manufacturers were carving out their own niche with small-capacity, affordable, and reliable two-wheelers aimed at commuters and first-time riders. Honda set up their first US dealership in 1959, closely followed by Yamaha, Suzuki, and Kawasaki, all offering an array of simple, lightweight, and utilitarian motorcycles. Extremely popular was the 50cc Honda Cub, whose 'You meet the nicest people on a Honda' advertising campaign did away with the leather-clad rebel biker stereotype, and instead presented motorcycles as a fun mode of transport for just about anybody.

Going Bigger

Having established a strong presence in the U.S. market with an array of 125, 250, and 300cc machines by the mid ‘60s, Honda now wanted to tap into the growing demand for performance-oriented motorcycles - a segment so far dominated by Triumph and BSA with their 650cc twins. Their first attempt to break into this space was with the 1965 Dream CB450, powered by a DOHC parallel twin. While smaller in capacity than the British 650s, the Honda motor was technologically more advanced, and hence delivered comparable performance while being more refined and reliable than the competition. Unfortunately, the belief that bigger was always better ran strong through the American biker community, and riders couldn't imagine picking a 450 over a 650. As a result, the CB450 wasn't the success Honda envisioned, and it was back to the drawing board.

Setting Targets

Yoshiro Harada, head of the CB450 project, wasn't too happy with the lukewarm reception his creation received and was still looking for a way to break into the American performance bike market. He knew that they had to go bigger this time, especially having received information that Triumph was working on a high-performance 750-cc triple for the upcoming Trident. By late 1967, the decision was finally made; Honda's large-capacity challenger would be powered by a four-cylinder 750-cc, air-cooled motor that would make no less than 67 horsepower, achieve a top speed of 120 mph, and cover the quarter mile in 13 seconds.

The Four-Cylinder Challenge

While mainstream production motorcycles with more than two cylinders were practically unheard of at the time, Honda was no stranger to lightweight, multi-cylinder engines. The brand's racing department had built a reputation as masters of engineering innovation, developing the high-revving four- and even six-cylinder competition machines that dominated the Grand Prix Motorcycle Racing World Championship through the 1960s. The high cost and complexity involved with designing and building multi-cylinder engines kept them confined to the racetrack, but now Harada and his team of engineers were faced with the daunting task of translating Honda's enigmatic motorsport developments into a reliable, road-going motorcycle that could be mass-produced, affordably priced, and usable by everyday riders.

Creating the World's Best Bike

Harada's brief for the CB750 was simple: better handling, braking, comfort, and refinement than any of the competition, while also being more reliable and offering longer service intervals. In essence, the team was instructed to build the best motorcycle that the world had ever seen. The landmark engine, while inspired by Honda's Grand Prix machines and sharing their air-cooled, inline-four-cylinder architecture, was designed for comfort, refinement, and everyday usability rather than outright power and high revs.

From Race Engine to Production Engine

Creating the CB750's four-cylinder engine was a lot more complicated than simply scaling up Honda's championship-winning race motor. After all, race engines are high-strung beasts that are designed to work best close to the limit, sacrificing real-world usability and durability in the pursuit of every last horsepower.

Honda's four-cylinder Grand Prix engine from the early ‘60s was a masterpiece at the cutting edge of internal combustion technology, revving up to over 14,000 rpm and generating approximately 45 horsepower from its diminutive 250cc capacity. On the other hand, the engine that Harada and his team created for the CB750 was a much simpler machine, designed specifically for everyday usability. While the short-stroke race engines that it was descended from were designed to rev to the moon, the new motor was intentionally undersquare with the stroke length longer than bore diameter - an architecture that prioritizes low-rpm torque generation. Similarly, the race engine got dual camshafts and four valves per cylinder to manage breathing at high rpm, while the CB750, designed to rev no higher than 8,500 rpm, made do with an SOHC, two-valve-per-cylinder layout. Also, the complex and expensive to produce gear-driven valvetrain employed in the race engines was foregone in favor of a traditional cam chain.

The Superbike is Born

It was at the 1968 Tokyo Motor Show that Honda revealed the machine that would redefine performance motorcycles. The Honda CB750 drew massive crowds to the Honda stand, its wide, heavily-finned, four-cylinder engine mounted transversely within the bike's frame looking downright futuristic compared to the singles and twins that had dominated so far. Aside from the motor, the CB750 was also among the first mainstream motorcycles to get a disc brake and an electric starter, while its modern styling immediately made the existing British twins look extremely outdated. And they were outclassed, too. The bike was extremely well received by the pubic as well as the motorcycle press, with Cycle World magazine referring to it as a ‘superbike', acknowledging how far ahead of the competition it was in terms of performance, refinement, and technology, and coining the term that is used to this day to describe high-performance sport motorcycles.

Taking Over the Market

When the CB750 hit the American market in 1969, it was an instant success that soon transformed the motorcycling landscape. That big lump of a motor with four carburettors and a row of shiny headers leading to four individual exhausts was like nothing the world had ever seen before. Sure, German bike manufacturer Münch beat Honda to a production four-cylinder motorcycle with their Mammut, powered by a 1.2-liter, four-cylinder NSU car engine, but the CB750 brought this exotic layout mainstream and made it accessible to the common man. Riders who had long accepted British twins with all their quirks now had access to a motorcycle that was faster, smoother, more reliable, and easier to live with and maintain. The smaller Japanese bikes had already proven themselves to be better built and less prone to oil leaks than their British rivals, and the CB750 brought these attributes to the large-capacity performance bike segment.

CB750 Legacy

Kawasaki, Yamaha, and Suzuki soon followed Honda with their own large-capacity inline-four-powered motorcycles, effectively ending decades of British and European bike market dominance. What began as Honda's ambitious attempt to break into the performance bike space ultimately reshaped the entire industry, establishing the transverse inline-four layout as the default formula for high-performance motorcycles for over half a century.

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This story was originally published May 9, 2026 at 6:00 AM.