2007 Honda CFR450R - Development

The Golden Age of Motocross Shines Brighter Yet in 2007

Without a doubt, from the perspective of the everyday rider, we are now living in the golden age of motocross machinery. In decades past, the factory teams sported incredibly trick, handmade unobtanium machines created exclusively for racing. Sure, some technology would trickle down to the showroom floor, but a yawning chasm always stretched between factory and production machines. The average Joe could never hope to own a machine with performance parameters that approached the factory level.

No such gap exists today; just take a look at any given weekend's AMA Supercross or motocross program and you'll see a huge contingent of privateers, mostly mounted on Honda CRF®450Rs, doing battle with the full-on factory racers - and doing much better than merely holding their own. The top 10 is often evenly divided between factory riders and privateers, and a podium spot is no longer just a privateer dream, as Nick Wey and his CRF450R proved in the 2006 Supercross series. No wonder the CRF450R remains the best-selling motocrosser.

For Honda, the process of evolution and change within the stock machine never stops; development is a never-ending task and significant improvements are slated for production virtually as soon as they become proven. There is no better example of this real-time development than Honda's Unicam® four-stroke engine. The popularity of this new-generation engine design - technology that's available in the CRF250R, 450R and CRF250X and 450X off-road models - is easily measured: Since the introduction of the 2002 CRF450R, more than 100,000 Unicam-powered CRF models have been sold. Constant development is one reason this engine package is so popular.

As one Honda engineer stated, "Development is a year-long process. Before the 2006 CRF450R even made its debut, we were already working on new ideas for the 2007 model. In addition to the R&D work done by Honda engineers, we're also in constant communication with the race team so we can pick up ideas there. And now that the 2007 CRF450R is here, the results are truly impressive, especially in the engine.

"We thought we had developed the perfect engine package in 2006, as far as driveability was concerned. But the 2007 engine is even better. We thought the 2006 CRF450R had great power everywhere, but now the 2007 450R has even more power all through the rev range, and the power characteristics feel markedly freer-revving in nature. In short, driveability is much improved, so lap times are down. All in all, the changes incorporated from 2006 to 2007 resulted in a bigger difference than the improvements from the 2005 CRF450R to the 2006 version."

Charting the major changes in engine hardware reveals no infusion of new technology; that's the nature of evolution within a package that has already more than proven its worth. The major alterations for 2007 include:

  • Smaller exhaust valves, from 31mm in 2006 to 30mm, and reshaped exhaust and intake ports for enhanced low-end/midrange power
  • A larger carburetor for increased top-end power, up from 40mm to 41mm, plus a new accelerator pump actuation system for quicker response
  • New clutch basket for increased durability; more silicon content now makes the basket harder and stronger

These changes for 2007 yield significant power gains throughout the rev range. The biggest area of improvement can be found in off-idle response and the feeling of more torque throughout the powerband. In real-world terms, this means you can take corners a gear higher than before, because the engine is so willing to pull a taller gear. With less shifting required, you can make up time all around the track. In addition, throttle control has also become much easier; with more bottom end and increased power throughout the upper rev range, throttle response has not only become more linear, but there's also more power all the way through to the top end.

Better yet, reaction to throttle input is now quicker than ever, thanks to a more direct linkage system for the accelerator pump. By eliminating the previous spring-loaded arm, the new simplified system yields more direct throttle response for more accurate control.

Fine-tuning in the chassis department likewise yields readily perceived handling improvements. The front suspension features new valving for 2007, including changes to the secondary compression stack for less compression damping mid-stroke. This alteration affects the character of the fork, producing smoother, more linear and more controlled response from mid-stroke through full compression for better control and feel. Primary compression valving settings have also changed, and a different shim stack changes the main compression settings as well.

Borrowing a page directly from the race team, Honda's engineers outfitted the 2007 CRF450R with a new linkage-type front brake lever for increased power over the previous configuration. This patented Honda design features a straight-line actuating system that yields more mechanical leverage to increase stopping power 15 percent without increasing rotor diameter or caliper size. Net result: The front brake is now much more powerful, and positive in feedback, feel and braking action for quicker stops. With a dramatic reduction in effort - this is now a one-finger brake system - you'll wonder how you ever got by without it.

To further enhance handling, the 2007 CRF450R features a newly developed Honda-exclusive Dunlop D742FA front tire in size 80/100-21. Just one glance at this new tire hints at its higher performance capabilities, thanks to its distinctive appearance, innovative knob pattern and profile. This tire holds a significant advantage in traction over the previous-generation front tire, especially in mid-corner. With great front-end feel and better traction across the board - in hard pack, muddy conditions, sand washes and more - this tire contributes significantly to the CRF450R's excellent steering characteristics.

To provide more handling advantage, the 2007 CRF450R now features an exhaust pipe and silencer that has been moved 22mm forward for an improvement in mass centralization. As a result, turn initiation with the big CRF is now easier and maneuverability is enhanced to save the rider's energy expenditure over a long moto.

And that's the way it is in 2007. Subtle, yet significant changes to the Honda CRF450R have combined to make a spectacular machine better than ever. Indeed, this is a great time to be riding motocross.

Honda's Innovative Unicam Design

With more than 100,000 Unicam engines setting the pace in motocross and off-road races across the country in the CRF250R, 450R, CRF250X and 450X models, Honda's innovative four-stroke technology has earned a performance reputation second to none.

The CRF450R's high-tech, liquid-cooled four-valve, four-stroke engine boasts a bore and stroke of 96mm x 62.1mm, yielding a displacement of 449cc. But the heart and soul of the CRF450R engine centers on the innovative Unicam single-overhead-camshaft (SOHC) design, which incorporates a carburized single camshaft that directly actuates two 36mm titanium intake valves. The camshaft's single exhaust lobe actuates two steel 30mm exhaust valves via an unique forked, low-friction, roller rocker arm. Valve adjustment is accomplished with shims; the intake valves use a direct shim-under-bucket system, and the exhausts incorporate shims between the rocker arms and keepers.

The titanium intake valves weigh only 24.8 grams each compared to 40.0 grams for a steel valve. Lightweight valves help create a high-revving engine, but with the CRF450R the primary focus is on saving space. A lighter valve permits the use of a smaller valve spring, which takes up less space in the cylinder head. This allows the camshaft to sit lower in the head for a more compact engine and lower center of gravity. The steel exhaust poppets handle the stratospheric 11,200-rpm rev ceiling just fine - this engine can scream!

The roller bearing on the rocker arm reduces friction and therefore wear, so the cam lobe can be narrower - and lighter - than conventional designs. The compact SOHC configuration and a separate cam holder contribute to a notably compact design that saves 13.3 ounces over a comparable DOHC motor, and also permit a narrow 21.5 degree included valve angle. This, in turn, flattens the combustion chamber to facilitate free flame propagation, allowing a high compression ratio of 12.0:1.

The CRF450R's Dual Oiling System Contributes to the Unicam Engine's Compact and Powerful Design

The CRF450R utilizes vertically split crankcases. As an interesting innovation, the oil pump is built into the left-side crankcase instead of using a separate pump housing, eliminating 5.1 ounces. In addition, the five-speed gearbox incorporates its own separate lubrication system, just like a two-stroke engine. Separating these systems makes for a smaller oil pan, reduced weight and less power-robbing oil-induced drag around the crankshaft. In addition, the oil bath surrounding the eight-disc clutch experiences a lower heat load.

Honda's Fourth-Generation Frame Graces the CRF450R

For 2007, the bulk of the CRF450R's chassis changes center on suspension refinement. But the heart of the bike's amazing handling is its fourth-generation aluminum frame. Honda has been crafting aluminum CR® and CRF frames for 11 years now, and the CRF450R's fourth-generation frame reflects Honda's accumulated expertise and state-of-the-art thinking.

Like all of Honda's aluminum frames, the CRF450R frame is purpose-built and tuned specifically for the 450R. By tuning the flexibility of this frame, Honda engineers balance lightweight agility with frame rigidity. This is one of aluminum's great advantages. Material can be added and taken away to gain strength or flexibility in specific areas. Furthermore, because the main spars of Honda's aluminum CR frames are rectangular in cross-section, engineers can work with two more variables unavailable to round-tube-steel fabricators. First, they can make the top and bottom sections of the box thicker or thinner than the sidewalls, simply by specifying a change in the extrusion dies. This can alter the stiffness of the frame members in a substantial yet precise way, making them resistant to up-and-down flex while still allowing side-to-side resilience.

With this fourth-generation aluminum frame, Honda's engineers took advantage of the material's amazing tunability everywhere. The semi-double-cradle design incorporates a forged-aluminum steering head. A forged gusset at the rear of the steering head adds strength to the entire assembly. This steering head connects to a single, tapered, large-diameter downtube that is beefier on the 450 than on the 250, as one would expect given the 450's bigger engine. Swingarm pivot plates feature a web of internal gussets for increased strength, and are shaped to create a narrow overall cross-section to optimize rider comfort and enhance maneuverability. The most visible distinction of the 450R's fourth-generation frame are the main spars connecting the most crucial chassis elements: the steering head and the swingarm pivot. These lightweight aluminum extrusions are shorter, narrower, and feature thicker walls than Honda's third-generation aluminum frame.

Compared to the third-generation frame, the flex characteristics of the fourth-generation frame create a chassis that feels softer on bump impact and improves cornering characteristics, while still delivering the solid handling and exemplary level of durability Honda's aluminum frames are known for.

In addition to its structural changes, this fourth-generation frame uses enhanced geometry to add even more handling benefits. This frame helps lower inertial mass and moves the 450R's center of gravity forward to help achieve the desired feeling of light, nimble handling.

The end result is a world-class chassis that continues to establish handling standards for riders of all abilities. Combine the CRF450R's user-friendly handling with its wide powerband, and you have a design that appeals to riders of all skill levels.

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