Engine

The new CBR600RR is no mere styling exercise based on a higher-tuned version of the CBR600F's well known and highly regarded engine. Instead, its new 'RR' version powerplant was designed from the ground up to provide an all-conquering blast of track and street performance that will leave no mistaking who's riding with the winners in 2003. With a much more circuit-oriented mission dedicated to unrivalled racetrack dominance, the CBR600RR's development team concentrated on refining the fundamentals of high-performance engine design with a host of major improvements and new concepts forged in the fires of Superbike and MotoGP competition.

Interestingly enough, extensive testing of various combinations of bore and stroke sizes found that the current CBR's displacement figures were also ideal for the new 'RR's performance targets, so no changes were made to the engine's basic displacement figures, which remain the same as the current CBR600F. Instead, efforts were focused on achieving improvements in engine performance through both a smaller and lighter design, reduced mass and friction and more efficient combustion characteristics. This was ultimately achieved through two major changes in the engine's design.

A Narrower Profile

With the goal of achieving a major increase in cornering clearance and banking angle, the engine's width was reduced at the crankshaft through the repositioning of several key components. First, the crankshaft's starter gear was moved from its current location on the left, behind the ACG, to the right, which freed up room to move the ACG itself further inboard, and reduce the dimensions of its cover accordingly. The distance from the engine centreline to the outer perimeter of the ACG cover was subsequently reduced by 21.5mm. This change alone, combined with a shift of the engine's centreline relative to the centreline of the frame, and the newly designed ACG and clutch covers with their deeply tapered underside corners, effectively narrowed the width of the engine to realise a significant 3° increase in bank angles for each side, while ensuring more than ample cornering clearance at all-out racing speeds.

A Shorter Engine Length

Another major goal in the new engine's design was to shorten its length, thereby freeing up space to lengthen the swingarm and move both engine and rider forward-closer to the steering head and closer to the machine's overall centre of mass-in a quest for quicker, more responsive manoeuvring and sharper, more assured cornering control.

Until now, the most conventional approach to crankcase construction has been to line up all the major shafts in a row along the dividing line between the upper and lower halves of the horizontally split cases; a design that greatly facilitates crankcase assembly. However, this basic design also inherently places limits on the length to which the cases can be shortened, as all the interim gears positioned between the crankshaft and the final countershaft have fixed diameters that can't be made any smaller.

In order to free-up room to move the case-mounted swingarm pivot closer to the crankshaft, the CBR600RR's engine design team raised the centrally positioned main shaft nearly 50mm above the case centreline. This permitted the countershaft to be moved closer to the crankshaft in a triangulated layout which resulted in a 30mm reduction in the distance between the crankshaft and the rear swingarm pivot.

To further enable the new engine to be positioned 9mm farther forward, the cylinder head's exhaust ports were angled downward a full 30° compared to the current CBR600F's engine to allow the exhaust system to curve in closer to the front of the engine, effectively shortening the engine at the front, as well.

This shorter engine length subsequently permitted the swingarm to be extended in length by 43mm for more progressive suspension operation and reduced stresses on the drive chain through the swingarm's range of movement.

Lightweight, New 'Slipper' Pistons

Minimising reciprocating weight and mass were also important goals in design of the new CBR600RR's engine in the quest for both higher rpms and higher power while maintaining top reliability. The engine's new skirtless forged 'slipper' pistons are significantly shorter and 15g lighter than the pistons currently used by the CBR600F and F/S. Each piston's set of advanced, lightweight and-at 0.8mm thickness for the top ring-ultra-thin rings boast superior resistance to power-robbing flutter at high velocities, and to blowby when high piston speeds meet high compression-characteristics augmented by the Honda-developed PMC (Powdered Metal Composite) aluminium/ceramic cylinder sleeves in which these pistons slide. For further minimised reciprocal weight, the pistons are mounted to the ends of their connecting rods by way of shorter, smaller diameter, and 8g lighter tool steel wrist pins.

'Nutless' Connecting Rods

Connecting rods also play a big part in helping to achieve peak power-producing engine speeds, and excessive weight or mass here slows response and acceleration while introducing vibration and stress that can adversely affect operation at higher rpms. The new CBR600RR's connecting rods feature a lighter 'Nutless' design first pioneered on the VTR1000F and VTR1000 SP-2, which use standard threaded bolts screwed directly into tapped holes in the body of the rod, instead of the conventional nut and bolt combination used in most rods to hold their endcaps in place. Requiring only one tool to assemble, the new design is 12g lighter than the conventional bolt and nut combination, for a total weight savings of approximately 35g per cylinder, or 140g overall. This significant reduction in reciprocating weight makes a major contribution to reducing the engine's mechanical load to help the new CBR600RR achieve a much more aggressively sharp feeling of responsive acceleration.

The RR's new connecting rods have also been carburised for an ultra-hard outer surface that ensures an optimal balance of strength and durability over the course of riding and racing extremes.

The end result of all these improvements is a quicker-revving engine that produces strong power throughout its wide rev range and almost instantaneous bursts of blistering acceleration.

New Dual-Pivot Camchain Tensioner

At the howling top revs that the new CBR600RR's engine was designed to reach, concerns about precise cam timing and reliability come sharply into play. One main component that plays a crucial role in the CBR's valve drivetrain operation is its cam chain. At revs approaching 15,000rpm, not to mention the violent thrashes of acceleration and deceleration a motorcycle is exposed to over the course of a road race, the camchain comes in for especially hard punishment. Conventional spring-loaded camchain tensioners simply aren't up to job of maintaining steady pressure and tension on the chain under these conditions, so the CBR600RR's engine designers countered this potential problem with a simple yet ingeniously effective dual-pivot tensioner system.

Featuring a new two-piece configuration, the long standard camchain guide that extends upward from just above the crankshaft gear is now held by a short overlapping secondary guide that gives the tensioner preload spring much greater leverage to hold the chain steady under racing's violent stresses, and maintain precise valve timing throughout the new engine's ultra-wide power band.

Next-Generation Dual Sequential Fuel Injection System (PGM-DSFI)

Fuel and air management has come a long way in a few short years, with the latest fully mapped and digitised fuel injection systems not only providing quicker starts, sharper response and more powerful performance, but achieving all this while consuming far less fuel and releasing far less in the way of harmful exhaust emissions. Great strides have also been made in delivering smooth and steady low-speed performance for smaller, mid-displacement engines, with comfortably linear control in the lower revs making a major contribution to easier driveability in urban traffic conditions.

However, while current systems provide excellent performance for most on-road riding applications and engine speeds, the new CBR600RR was, from its inception, intended to deliver strong power all the way up to a blazing 15,000rpm power peak. At such engine speeds-and incredibly short intake and exhaust stroke intervals-the limits of current fuel delivery system configurations were soon found. Specifically, while fuel injected into the intake ports at close proximity to the opening valves does provide excellent response and strong power output at low-to-midrange operating speeds, at higher intake velocities the fuel spray simply doesn't have enough time or distance to fully atomise and adequately mix with the in-rushing air to provide the optimum air/fuel mixture needed for efficient combustion, and thus strong power output.

To counteract this phenomenon, the CBR's engine design team first tested and then installed another full set of four 12-hole injectors, positioning them high in the roof of the airbox. This second set of injectors has been programmed to only operate when the throttle is opened wide at engine speeds of approximately 6,000rpm, resulting in a significant boost in fuel intake and combustion efficiency at high speeds.

Opening a tiny fraction of a second before the main injectors on each intake stroke, this auxiliary set of injectors primes the air rushing into the velocity stacks of the lower throttle bodies with a more finely atomised spray of fuel. This highly accelerated air/fuel mixture is further enriched by the normally timed injectors installed in the new larger throttle bodies (up from 38 to 40mm), which release a precisely modulated volume of fuel into the mixture rushing into the combustion chambers to ensure stronger, more complete combustion at high engine speeds.

In order to realise the much higher-accuracy sequential control needed to effectively operate this total of eight injectors at the RR's ultra-high engine speeds, a new ECU system was also required. This newly developed 32-bit processor-based system replaces the 16-bit processor used in the current CBR600F's fuel injection system to achieve phenomenally higher speed operation and accuracy for top performance all the way to the engine's breathtaking redline.

Another important benefit of this new system is that the pre-charged induction also significantly cools the air flow through the throttle bodies and intake ports, resulting in a much denser charge of air/fuel mixture into the chambers than could otherwise be achieved in a normally aspirated engine at such a blazingly fast intake stroke interval-at 15,000rpm, a mind-boggling 125 openings and closings of each intake and exhaust valve every second.

The end result of this new injection system-coupled to the CBR600RR's smaller and lighter engine-is hotter and stronger combustion, and sharper, more responsive acceleration for stronger performance throughout its wider powerband, as well as a breathtaking boost in peak power output.

Low Emissions for Environmental Protection

The new CBR600RR is also equipped with Honda's latest secondary Air Induction system. Featured on most of Honda's larger displacement motorcycles, this system complements the precise metering of its advanced fuel injection system with the introduction of an extra charge of fresh air into the exhaust ports on the exhaust stroke to extend the burning of exiting exhaust gases into the exhaust port, thereby ensuring more complete combustion and reducing pollution emissions to a level that easily complies with EURO-1 regulations.

CBR600RRs destined for Germany will further be equipped with Honda's advanced HECS3 oxygen-sensing catalyser system to ensure full compliance with current EURO-2 emissions regulations. Performance differences between the two versions will be minimal, and virtually unnoticeable to even the most discerning rider.