Six cylinders and turbos: what the 2021 Suzuki Hayabusa could have had

Above: The 2021 Hayabusa and its ancestors. It could have been very different.

In the yawning 13-year chasm between the launch of the second-generation Suzuki Hayabusa and the brand new 2021 model there’s been no shortage of rumours and clues to Suzuki’s development work on the machine. And while the final version has specs that don’t differ vastly from its predecessor Suzuki has taken the unusual step of confirming the truth behind the stories that emerged over those years.

So while some might be disappointed that the final 2021 Hayabusa has similar specs to its predecessor, and a slight reduction in peak power, it’s clear the decision to take that path wasn’t taken without exploring a variety of other avenues including a potential six-cylinder Hayabusa, a turbocharged four-cylinder and a bigger-capacity model.

Naoki Mizoguchi, engine designer on the Hayabusa project, confirmed the existence of the other prototypes, saying: “We considered a variety of engine configurations before arriving at the final design. Experimentation included building prototypes with larger displacement engines, turbocharged versions, and others with six cylinders.”

Yuichi Nakashima, who’s had the arduous task of test-riding prototypes right from the original Hayabusa to the final 2021 model, added: “I was tasked with riding turbocharged Hayabusa prototypes, those with larger displacement engines, and others with six cylinders. A large number of such prototypes came and went over the past 10 years.”

Assistant Chief Engineer Kenichi Kasuya also mentioned the alternatives, saying: “We experimented with a variety of possible designs for the new Hayabusa over the course of 10 years, building a number of different prototypes along the way, only to go back to the drawing board. Some of the variations included those with different frames, with engines of different displacement, or that employed a different number of cylinders.”

The boosted Busa

The idea of forced induction for the Hayabusa has been around nearly as long as the bike itself. Presented with the fastest and most powerful production motorcycle ever made in 1999, tuners went straight to work making it even quicker and Suzuki itself wasn’t far behind.

The closest the firm ever came to officially making a boosted Busa came when it presented the naked B-King concept bike at the Tokyo Motor Show nearly 20 years ago in 2001. Armed with a supercharged version of the original Busa’s 1298cc four, the concept was rumoured to be good for 240hp, driving through an unprecedented 240-section rear tyre. It was just a rumour, though; the original B-King concept was a mock-up rather than a runner. Such was the positive reception to the concept that Suzuki made the unexpected call to create a production model, but its development took far too long to cash in on the excitement around the idea. By the time the showroom version was ready in 2007, minus the blower and losing the cartoonish proportions of the concept, other fast naked bikes had moved the goalposts.

Suzuki’s turbocharged Busa prototype itself has never been shown, but the firm filed patents in 2015 thar revealed a turbocharged, four-cylinder bike showing the direction of the project. Based around the then-current GSX-R1000’s four-cylinder engine, it featured not only a turbo but two electric motor/generator units and a battery pack to be a true high-performance hybrid. As on the current generation of F1 cars, one of these motor/generators was attached to the turbo, spinning its compressor up on demand to eliminate turbo lag and regenerating electricity when the throttles were closed. The second, larger electric motor was mounted above the transmission, providing an additional boost of power and torque to fill in any holes in the petrol engine’s delivery and recharging the small, under-seat battery packs during deceleration.

Would it have been impressive? Without a doubt – a turbocharged 2015-spec GSX-R1000 engine with an added boost of hybrid power could easily have knocked on the door of 300hp. But it would also have been immensely expensive to develop from prototype to production, potentially leading to a showroom price that few riders would be able to afford.

Suzuki has showed a huge interest in turbo bikes, in particular working on the 700cc, parallel twin ‘XE7’ engine that it unveiled at the 2015 Tokyo Motor Show and which is still under development now.

The six cylinder that nearly happened

As a machine that’s all about excess, the Hayabusa was the most obvious target when Suzuki started to develop a six-cylinder in the early-00s.

The six broke cover in 2005 as one of the most stunning concept bikes ever to take pride of place on a show stand – the Suzuki Stratosphere. The firm had managed to keep the project secret and, having learnt a valuable lesson from the B-King mock-up it presented four years earlier, added to the surprise of the Stratosphere by revealing it was a complete, running machine at the time of its unveiling.

With an 1100cc, water-cooled six, the Stratosphere promises similar performance to the then-current Busa – with around 180hp on tap compared to the first-generation Hayabusa’s 173hp. The engine was clearly related to the GSX-R fours of the era, and Suzuki was on the crest of a wave when it came to engine development, with the GSX-R1000 and 750 of the era setting class-leading standards.

The Stratosphere itself hinted at Suzuki’s interest in reviving the style and stance of the Katana, buts its long, low proportions and its riding position – sporty but not too extreme – put it spiritually closer to the Hayabusa than anything else.

Given that the engine was proved to be a runner (Suzuki showed videos of the bike moving under its own power at the Stratosphere’s unveiling) it’s clear the intent was much greater than merely creating a show-stopping concept bike. The Strat’s engine is very likely to be the basis of the six-cylinder prototype that Suzuki’s Hayabusa engineers have been experimenting with over the last decade or so.

Semi-auto boxes and new frames

Another element of the Suzuki Stratosphere that appears to have come close to making into production before falling by the wayside was its semi-automatic transmission.

Created using a conventional box with an electric servo taking on the shifting duties instead of your left foot, it was envisaged as an easy-to-implement setup that could be operated manually or fully automatically depending on rider preferences and, for several years, patents emerged from Suzuki showing exactly such a setup implemented on a Hayabusa.

Suzuki hasn’t mentioned the system with the launch of the new bike, but the adoption of an up-and-down quickshifter on the 2021 model – including two operating modes as well as an ‘off’ setting – could well explain its absence. The reality is that semi-auto boxes are starting to look like something of a development dead-end because modern quickshifter technology allows clutchless up and down changes without the complexity and unfamiliarity that a true semi-auto brings. The value of shifting in terms of keeping the rider and bike working in harmony is also being appreciate more today., Even some electric bikes are adopting multi-gear transmissions purely to enhance rider interaction.

On the chassis side, we’ve seen several patents over the last few years showing a Hayabusa with a sportier, lighter-looking alloy beam frame. The design that Suzuki was working on appeared to be more like the GSX-R1000 frame, without the huge seat subframe support that’s used on the Busa, but once again it appears that the disadvantages of a redesign outweighed the advantages. Hayabusa chassis designer Takeshi Yoshida said: “We tested a number of completely different frame designs. Considering the Hayabusa the two-wheeled equivalent of a supercar, we decided to continue using the same extruded aluminium on the frame that is also used by its four-wheeled counterparts. This enabled us to build the best possible frame for the new Hayabusa.

“When I look at the final product, I am once again convinced that we made the right decision in basing the new Hayabusa around the tried and true frame of the previous generation.”

Above: Naoiki Mizoguchi, the Hayabusa’s engine designer, confirmed turbo, six-cylinder and bigger-capacity versions were tried.

Big-bore Busa

One of the most persistent recent rumours about the next-gen Suzuki Hayabusa was talk of an enlarged version of the existing four-cylinder engine. Japanese sources were, until recently, adamant that the next version of the bike would get a 100cc capacity hike to 1440cc.

Given recent trends, it’s a move that made a lot of sense. The adoption of Euro5 standards has imposed strict new limits on certain types of exhaust emissions, making it particularly difficult for manufacturers to pursue the traditional route of boosting power by increasing revs.

As a result, we’ve seen a number of bikes get big-bore engines in response to the new rules, from Triumph’s new 1160cc Speed Triple to the Yamaha MT-09 and Honda Africa Twin. A 100cc capacity increase on the Hayabusa might well have been just what it took for the 2021 version to be introduced without the slight reduction in peak power – down from 195hp to 188hp – that has come by sticking with the previous 1340cc engine size.

With new pistons anyway, and plenty of president from tuners to show that the engine can be made bigger, the capacity increase wouldn’t have been hard to achieve, but the firm hasn’t opted to take that route. It was a balancing act, and Suzuki has focussed on building on the Busa’s already impressive reputation for strength rather than risking it by pushing for more performance out of the box.

Engine designer Naoki Mizoguchi said: “We thoroughly examined every engine component. The pistons and connecting rods were redesigned. The crankshaft is basically the same, though we made refinements to improve durability.

“The development process included testing the engine time and time again. I believe an engineer’s job is to identify any potential weak spots and reinforce them to build a more durable engine.  That is what leads to enhancing the levels of both performance and durability.”

Engine Test Engineer Shunya Togo adds: “Although the Hayabusa engine was already renowned for outstanding durability, we thoroughly studied the second-generation engine while striving to evolve it to a higher new level. We reviewed every single bolt and O-ring while sharing opinions with our engine designers on how best to improve them. We even changed the method of tightening the engine case bolts. As a result we addressed every basic components and increased the overall strength of the engine.”

There’s a tacit acknowledgement from Suzuki that owners who want more performance than the stock Hayabusa can offer are going to start tuning it anyway. By making the engine as strong and reliable as possible out of the box, it becomes all the better as a platform for aftermarket options to hike the power levels higher.

Mizoguchi said: “We worked so hard to ensure the quality and durability of the engine and hope to see customers ride the new Hayabusa for 100,000, 200,000 or even 500,000 kilometres.”

Test rider Nakashima found the alternatives weren’t an improvement over the current design.

In the end, Suzuki was clearly faced with a dilemma: did the alternatives provide something that an updated version of the original Hayabusa couldn’t achieve, and would the benefits outweigh the massive cost of putting a more heavily reengineered bike into production? Costs that would, of course, be passed on to customers.

Engine designer Mizoguchi says that the alternatives couldn’t make a persuasive argument for themselves. “In the end,” he said, “We came to the conclusion that the original engine package achieved the best overall balance. We also came to the conclusion that not changing the basic layout was key to retaining the Hayabusa’s distinct identity. So we applied the best of its proven qualities when we sat down to set the latest engine design 20 years after the launch of the original Hayabusa. Our goal was to create a better engine while building on the same proven layout. That became the aim of our engine design efforts.”

Test rider Nakashima, who is better qualified than anyone to make such a judgement having actually ridden the alternative Busa prototypes, agreed, saying: “In the end, none of them proved superior to the current engine in terms of overall performance. Having worked as the test rider for the first and second generations, I gave my best effort to assuring that the new Hayabusa would be received as a worthy successor.”

And Toshihiro Suzuki, the firm’s president, agrees, saying: “Our designers faced a truly daunting challenge. The first generation Hayabusa had been such a big hit that the development team was left troubled over how best to evolve it and what changes to implement. I think the resulting form represents a natural evolution.” 

While it’s a shame we haven’t had a chance to try a turbocharged or six-cylinder Hayabusa for ourselves, the words of those who’ve been involved from the start mean it’s hard to argue that the firm has made an error in sticking to the tried and tested formula that’s worked so well for so long.