It was the second half of the 1980s. Having used its V4 racing engine on a wide range of commercial motorcycle models, Honda was seeking to apply the technologies it had developed in completely new types of motorcycle engine. One such initiative was the development of a next-generation inline 4-cylinder 1,000cc super sport bike engine featuring a side cam chain system that drove the camshaft from one side. This system generated more torsion than conventional central drive systems and therefore had durability issues that needed to be overcome, yet it made possible an engine that was extremely compact.
The 1,000cc-class super sport bikes of the time were big and imposing yet did not offer the kind of control that made them seem an extension of the rider. Use of the new inline 4-cylinder engine could make possible a high degree of freedom in super sport bike design, and Honda was considering how to leverage its potential in developing a total high-performance package.
This potential could perhaps prove of value in the world of racing as well. It was precisely because V4 engines were at their height of popularity that Large Project Leader (LPL) Tadao Baba and the rest of his CBR900RR development team wanted to explore what an inline 4-cylinder engine could do on the circuit. With the difficult objective of developing an engine that could defeat a V4, they built a 750cc prototype with bore and stroke of 70 mm x 48.6 mm that retained the basic design of an inline-4 1,000cc engine. Featuring superior pickup and acceleration characteristics in the mid to high rpm range, this engine was more lightweight and compact than a conventional 750cc V4 engine. In combination with a lightweight and highly rigid body, it had the power to offer riders an exceptional level of control.
Thereafter, the team transformed the project into developing a completely new type of super sport bike for Europe and the United States. Since the bike was no longer intended for racing, there was no need to stick to the 750cc displacement limit that racing regulations required. What was desired instead was the powerful torque that only a large-displacement engine could offer. Indiscriminately raising displacement, however, would simply result in another super sport bike that was too big and too heavy. The development team therefore decided to see how far they could increase displacement without deviating from the vehicle weight and dimensions of the 750cc advance research stage model. Determining that most riders needed to accelerate up to a maximum speed of 160 km/h, the team set out to achieve the same 0-1,000 m acceleration as a 1,000cc-class super sport bike.
The team ended up designing an 893cc engine offering output of 124 PS. While retaining the basic design of the 750cc engine, its stroke was 9.4 mm longer. The “900” in CBR900RR fit no established category, yet the model offered riders the joy of control at an unprecedented level, ending at once the era in which a super sport bike was judged merely by the displacement and engine output figures in the catalog. Thereafter, while competitors introduced bike after bike with a 1,000cc engine, the development team continued to favor displacement of 900cc. Instead of high power alone, total packaging was the key to delivering riders the ultimate joy of control and handling. This approach held true for the model changes implemented in 2000 and 2002.
Eight years had passed since the introduction of the original CBR900RR. While competitors were launching rival bikes with 1,000cc-class engines and an emphasis on outright power performance, Honda was increasing the power of its own CBR900RR to offer more riding enjoyment than any other bike. At the same time, the development team wanted to stay with a displacement figure that could justify the “900” in “CBR900RR.” They weren’t simply clinging to a beloved name. To them, “900” conveyed that the CBR900RR was not beholden to racing regulations but was designed for regular riders to enjoy riding on the street. In addition, “900” signified that Honda was not taking the easy route of competing for the highest engine output. Indeed, “900” symbolized the tradition and principles of the CBR series.
Looking for ways to increase displacement while sticking with “900,” the team found that the answer was relatively easy to find. The reason was that the dimensions of the vehicle had to remain fixed in order to fulfill the goal of offering riders total control. Since the length or width of the engine could not be increased, the obvious choice was to focus on cylinder bore. By decreasing minimum wall thickness between cylinders to 7 mm—to the minimum possible at the time—the team was able to increase cylinder bore from 71 mm to 74 mm, resulting in total displacement of 929cc.
In the case of a racing bike, it would have been a simple matter to use this increased displacement to achieve the desired maximum output figure of 148 PS. This method, however, was almost certain to sacrifice the ease of handling at low speeds that is essential on the street. With the goal of combining excellent low-speed handling with increased high-speed output, the team experimented with many devices, eventually developing H-VIX: Honda Variable Intake and Exhaust. The world’s first system of its type, this exhaust device used a servo motor to switch between two different exhaust pipe configurations. To enhance low-rpm torque, the system selected the 180º configuration, in which exhaust pipe No. 1 was combined with No. 2, and No. 3 with No. 4. To enhance high-rpm output, the system selected the 360º configuration, in which exhaust pipe No. 1 was combined No. 4, and No. 2 with No. 3. Up to 3,000 rpm, the system used the 180º configuration, from 3,001 to 7,000 rpm it used the 360º configuration, and from 7,001 rpm upward it used the 180º and 360º configurations simultaneously. Through this method, the system combined easy low-speed riding with exhilarating high-speed cruising. In addition, since it was made of ultra-lightweight titanium, this device enhanced responsiveness while also contributing to lightweight design. Control of H-VIX together with an intake device that adjusted the amount of air coming in through the air cleaner optimized output characteristics based on engine rpm. While maintaining the “900” figure, these systems enhanced not only output in the high rpm range but also rideability in low rpm range, where much street riding takes place.
Two years later, in 2002, the team succeeded in decreasing minimum wall thickness between cylinders beyond the theoretical 7 mm barrier to 6 mm and increased cylinder bore from 74 mm to 75 mm, resulting in increased displacement to 954cc. At the same time, they also reduced the weight of the engine’s reciprocating parts by 4 percent. While maintaining a level of rideability and control that have always been its hallmarks, the CBR900RR now offered even higher power performance.
The CBR900RR goes up to 290 km/h but offers smooth riding all the way. This was the concept behind the development of the engines for the fifth-generation CBR900RR (CBR929RR) and sixth-generation CBR900RR (CBR954RR). Not only did street riders testify to the exceptional rideability these models offered, but so did the CBR900RR riders and marshals participating in one of the world’s most grueling races: the Isle of Man TT Race. Said one rider, “This is the first super sport bike I’ve found so easy to ride on the Isle of Man.”
When the Superbike World Championship changed its regulations to allow 4-cylinder engines up to 1,000cc, Honda decided to switch its base machine for the competition from the VTR1000 SP-1/SP-2 to the CBR1000RR. While retaining the same cylinder bore and cylinder pitch, the development team extended piston stroke from 54 mm to 56.5 mm, thereby raising engine displacement to 998cc and maximum output to 172 PS. This latter figure was 24 PS higher than that of the preceding model and looked impressive on the spec sheet, but from the time the original CBR900RR debuted in 1992, Honda had never held that power alone was important. Rather, in developing the engine of the CBR1000RR, Honda’s goal was to produce real results on the street and on the circuit. In other words, the engine had to contribute to the design of a motorcycle body that would offer true depth of riding feel.
The team adopted the Unit Pro-Link rear suspension to increase the freedom of frame design, enhance competitiveness on the circuit and ensure a light riding feel on the street. It was therefore necessary to find extra space in which to implement this new system. Putting the crankshaft, mainshaft and countershaft in a new triangular configuration reduced the distance between the crankshaft and the swingarm pivot by 21.5 mm. Finally, lengthening the swingarm by 34 mm established dimensions that would let riders enjoy high power with peace of mind.
Creating an engine that could be trusted in the extreme environment of racing would also mean creating an engine that let riders enjoy riding on the street for extended periods with peace of mind. To enhance the rigidity of the cylinder block, a semi-closed deck structure was adopted in which bridges ran between the upper part of the cylinder bores and the outer wall of the block. While maintaining cooling performance, this structure enhanced durability and reliability and, along with newly designed forged aluminum pistons and a new nutless connecting rod, added to the overall refinement of the engine.
For the 2008 model, bore was increased from 75 to 76 mm, while stroke was shortened from 56.5 mm to 55.1 mm, taking engine displacement to 999cc. While offering greatly enhanced output characteristics, this new powerplant featured a newly designed engine case, independent cylinders and revised materials throughout, resulting in a 2.5 kg reduction in engine weight as compared to its predecessor.