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Kawasaki’s 2011 Supercross / Motocross race machines

Published May 27th, 2010

Here is the latest information from Kawasaki on their two primary race machines for supercross and motocross, the KXF 450, and the KXF 250.

In the 450cc motocross game, the only thing that matters to serious racers is top-tier performance and running up front. And for 2011, the best tool for the job is once again a lime green one Kawasaki’s reworked and revised KX450F. In this arena you can’t stand still technically, which is why Kawasaki engineers scrutinized every system and component of the race-winning 2010 model and came up with a host of tweaks that’ll have red, blue, orange and yellow wondering what hit ‘em.

The latest open-class KX starts with the primary pieces that allowed the 2010 KX to win more Supercross events than any other bike last year – a brutally fast 449cc DOHC four-stroke single packing a broad spread of power housed in a lightweight-yet-strong aluminum frame connected to a suspension designed to offer compliance, high-speed stability and whoop-sucking performance all moto long. It was an ideal platform on which to win the majority of races in 2010, and that trend promises to continue with the revised, even faster 2011 model.

Last year, the KX450F featured a number of engine refinements, including the first ever production use of a bridged-box bottom piston (more high-end power and better over-rev characteristics), revised cam timing for better mid- and top-end performance and a reinforced cylinder sleeve and crankcase for improved durability.

This year there’s even more. The bridged-box bottom piston shape, for instance, has been modified to meld with the upgraded, higher-volume muffler, which is quieter than last year’s unit. The ECU has been tweaked to provide a hotter and longer-duration spark for improved low-rpm response. The shift mechanism incorporates a larger internal roller and stronger shift-spring tension for more positive shifting. Finally, the fuel-injection system’s Calibration Kit software has been updated, while the controller harness and connector have been modified for easier use.

Changes in the chassis department are equally impressive, and show the results of our race team’s effect on development. First up are revisions to the engine mount brackets that optimize chassis flex and improve handling. Next, the engineers revised the damping settings for the massive fork tubes for even better performance. For that factory-bike touch there are also blue-anodized compression damping adjuster caps in place of last year’s silver ones. Damping settings on the rear shock have also been revised, and it, too, gets a blue-anodized compression adjuster. The seat features a new side-surface texturing for increased rider grip while aboard, and the drive chain guide has been thoroughly beefed up for increased durability; testing shows it to be nearly three times more durable than the unit fitted to the 2010 machine.

The race-ready engine is compact and light, with a short 100mm cylinder head and a 12.5:1 compression ratio. A wedge shaped crank web offsets 60 percent of the crankshaft’s reciprocating weight, producing an effective ‘counterweight’ effect. This is on par with Kawasaki’s factory racers and helps reduce engine vibration, smooths power delivery and enhances low-rpm throttle response. A stainless steel exhaust pipe connects to the revised silencer, which uses long-fiber packing material to maximize service intervals. A rubber damping collar in the rear silencer mount provides a boost to long-term durability. The KX450F’s Digital Fuel Injection (DFI®) automatically adjusts to suit track and climate conditions, and offers stable fuel metering even when landing from jumps in tough motocross conditions. The DFI system includes a compact and lightweight ECU, a 43mm throttle body, a lightweight aluminum fuel pump and an ultra-fine atomizing injector. Set at a 45-degree angle for ideal mid-range power, the 10-hole injector sprays precise, 60-micron fuel particles for smooth power delivery and accurate engine response throughout the rpm range. Designed specifically for supercross and motocross, the KX450F’s lightweight DFI system doesn’t require a battery; the engine can be started within three rotations of the crankshaft using only the electricity generated through the initial stroke of the kickstarter.

An optional ECU Setting Tool allows racers to select from several different ECU data maps, or fine tune a custom map that alters fuel injection and ignition timing to suit different tracks and conditions. The tool can also be used as a data logger, recording up to six hours of data, including engine rpm, degree of throttle opening, engine boost, coolant and air temperatures, ignition timing, fuel adjustments, gear position and system voltage.

The engine’s phenomenal power is delivered through a clutch that features an ultra-light operating plate with superb oil drainage and beefy friction plates. The entire assembly is designed to provide exceptional clutch feel and durability. The drive chain features thin inner links and a slight weight savings relative to typical designs to help boost acceleration. The revised suspension damping settings provide lighter handling, improved suspension action, increased comfort and greater cushioning when landing from jumps.

The 2011 KX450F’s D-shaped aluminum swingarm features a cross section with narrow ribs and thin walls. It pivots high in the aluminum frame to maximize rear wheel traction. Mounting the arm of the Uni-Trak rear suspension linkage below the swingarm provides a long rear suspension stroke and facilitates precise shock tuning.

Kawasaki's 2011 Supercross / Motocross race machines - Photo 1 of 2

2011 Kawasaki KXF 450

Complementing the responsive chassis is a Kayaba Air-Oil-Separate (AOS) fork that offers precise cornering and sharp handling. The fork features a Diamond-Like Carbon (DLC) coating on the outer surface of the inner fork tubes to minimize stiction when the fork is exposed to lateral forces that would otherwise restrict slide action. The result is smooth and precise response, especially during cornering. Overall suspension action is extremely smooth due to a friction-reducing Kashima Coat treatment on the inside surfaces of the outer fork tubes and the rear shock reservoir. Wrap-around fork guards provide excellent protection for the sliders.

The 2011 KX450F’s Kayaba rear shock’s revised damping settings contribute to improved wheel control and impact performance when landing from jumps. It features a large 50mm piston and a Kashima Coat treatment on the shock internals to help maintain a plush feel throughout the toughest motos. Easily accessible dual compression adjusters allow high- and low-speed damping to be tuned separately, giving mechanics and riders the ability to easily fine tune the suspension for difficult track conditions.

A slim seat design with firm urethane foam and a non-slip top and side surface provides even more seated and standing grip while retaining excellent rider mobility. The frame echoes the slim profile at the top, but widens at the lower end by the ankles to provide the rider with better feel and control. Completing the rider interface are wide 50mm footpegs that offer tenacious grip and a comfortable platform.

The 2011 KX450F is available in Kawasaki Lime Green, with black alumite-coated rims and aggressive graphics for a factory appearance.

Racers who ride their KX450F at designated events are eligible to receive support from Team Green, Kawasaki’s amateur racing support program. Each year, Team Green provides regional support vehicles and highly trained technicians at more than 100 events throughout the United States, offering technical information and assistance to those who race Kawasaki products. Kawasaki also offers a comprehensive contingency program for amateur and professional riders who place well at designated events.

More AMA 250 Lites Supercross and Motocross Championships than any Motorcycle in History!

It’s an old refrain: The factory guys get all the good stuff. Their bikes are faster, lighter and just plain tricker than the motocrossers you can buy off the showroom floor. There’s some truth there. But that’s changing. The gap between production and factory-prepped motocrossers has never been narrower. And with the introduction of Kawasaki’s massively reworked 2011 KX250F, that gap just shrank a little more.

Kawasaki's 2011 Supercross / Motocross race machines - Photo 2 of 2

The 2011 Kawasaki KXF 250

All told, there are nearly 30 upgrades to the new KX250F, all of which reflect the stunning level of testing and development happening behind the scenes at Kawasaki’s R&D and race teams. And Kawasaki does this for one reason: To put you on the fiercest, most capable motocrosser in the industry.

When reworking the new KX250F, engineers started with what’s arguably already the gold standard in 250-class racing – the 2010 KX250F. Just ask Christophe Pourcel and Jake Weimer, who won the 2010 AMA East and West Supercross Lites titles, respectively, on their Monster Energy Pro Circuit Kawasaki-backed KXs.

For 2011, the goal was an even faster and more ridable KX250F. On the more powerful side of the equation are loads of engine modifications, all of which have made the latest KX an absolute corner-to-corner screamer. The big news is the addition of Digital Fuel Injection (DFI®) that not only helps produce stunning – and more useable – power, but also makes tuning a much easier proposition. The system, basically identical to the one fitted to the 2011 KX450F, automatically adjusts to suit track and climate conditions, and offers consistent fuel metering and response even when the going gets rough, such as when landing off jumps or slamming through the whoops. The simple and highly efficient DFI system incorporates a compact and lightweight Electronic Control Unit (ECU), a 43mm throttle body, a lightweight aluminum fuel pump and an ultra-fine atomizing injector. Set at a 45-degree angle for optimum mid-range power, the injector precisely metered fuel directly into the intake tract for smooth power delivery and highly accurate engine response throughout the entire rpm range. The 250F’s injector actually flows more fuel than the 450F’s unit due to the 250F engine’s higher speeds, while airflow through the system is actually higher than through the 2010 model’s carburetor setup.

Designed specifically for supercross and motocross, the KX250F’s lightweight DFI system requires no battery; the engine can be started within three rotations of the crankshaft using only the electricity generated through the initial stroke of the kickstarter. What’s more, an optional ECU Setting Tool allows racers to select from several different ECU data maps, or fine tune a custom map that alters fuel injection and ignition timing to suit different tracks and conditions. The tool can also be used as a data logger, recording up to six hours of data, including engine rpm, degree of throttle opening, coolant and air temperatures, ignition timing, fuel adjustments, gear position and system voltage.

You’ll find more significant changes farther downstream, such as higher compression now 13.5:1 vs. 13.2:1 via a modified cylinder and changes to the top of the exclusive Bridged-Box Bottom piston. The intake camshaft now produces higher valve lift, while the intake valve spring is stronger to handle the extra load. The crankshaft’s rotational inertia has been slightly modified to better match the new engine’s characteristics, while a slightly longer spark plug design and a new coil offering a hotter and longer-duration spark improves combustion performance. Transmission and final-drive ratios have been altered slightly to match the engine’s newfound response, and a modified shifting mechanism allows you to access those speeds more easily and smoothly. There is 10% more air-cleaner duct volume for better breathing, and on the exhaust side, a longer head pipe gives the engine a touch more low-end power, while a higher-volume muffler assembly lowers noise to comply with the 94 db AMA Pro Racing limit, while retaining optimum power production up top.

The chassis has been massaged every bit as thoroughly as the engine, with Kawasaki’s new Separate Function Fork (SFF) leading the list of changes. Unlike a conventional fork design, where each fork leg handles both springing and damping, the SFF separates spring and damping functions for improved performance, 25 percent less friction, lower weight and easier adjustability. The right leg accommodates the spring side of the equation, incorporating a larger main spring/rod assembly than traditional forks, plus a small amount of oil for lubrication. Spring preload is now adjustable via a blue-anodized adjuster on the right leg’s cap. The left leg handles damping duty, with only its cartridge damper assembly and fork oil inside the tube. Rebound and compression damping are adjustable on the fork tube. In addition to the natural reduction in friction provided by the SFF design, the KX250F’s inner fork tubes are titanium nitride coated to reduce friction. Lower friction and better overall fork action are keys to the new fork’s performance, and they are traits you’ll appreciate the first time you charge into a bump-infested corner at speed. Fork offset has also been reduced by a full millimeter for lighter handling and quicker steering response.

Out back, the rear shock incorporates revised damping settings that more closely match the SFF’s performance. The result is even more wheel and chassis control while ripping across a set of whoops or shrieking through that fast, rutted corner leading onto the front straight. Like the KX450F, the new 250F gets a reworked seat with grippier material along the sides for improved rider grip while standing when the action gets hot and heavy.

The rest of the package includes the same top-tier components that have put the KX250F atop the podium for years. The KX250F’s aluminum perimeter frame, with its lightweight blend of forged, extruded and cast parts, has the chassis balance, rigidity and durability experienced riders want and need, and locates the engine, rider and pivot points where they perform best.

Designed with rider ergonomics foremost in mind, the KX250F’s bodywork offers riders a slim interface and a natural positioning that make going fast a simple affair. The sleek bodywork components include one-piece plastic shrouds and side number plates. The upgraded seat provides excellent seated grip and rider mobility, and features firm urethane foam to hold its shape longer. Chassis protection bits include the large, resin skid plate, rear caliper guard and a redesigned chain guide with approximately 2.5 times more durability than the 2010 unit.

The KX’s 249cc, liquid-cooled, four-stroke engine is a veritable powerhouse, and features an electrofusion cylinder treatment on the cylinder bore, a crankshaft balance factor of nearly 60 percent (on par with Pourcel and Weimer’s factory racebikes), for reduced vibration and smoother power delivery, a highly durable yet slick-shifting transmission, stronger-than-ever crankcases and a level of reliability that’ll keep you out there and on-track all season long. It’s been rated the best engine in its class by various magazine editors, and you’ll understand their thinking after your very first ride.

The rest of the KX250F package is every bit as impressive as the engine and chassis. Aside from the sort of fit and finish you expect from Kawasaki, ther”s also a premium-quality Renthal aluminum handlebar included standard, black alumite-coated aluminum wheels that are both light and strong, a ribless rear hub and butted spokes that further reduce unsprung weight, and factory-style graphics that finish things off nicely and highlight the KX250F’s amazing on-track abilities.

Racers who ride their KX250F at designated events are eligible to receive support from Team Green, Kawasaki’s amateur racing support program. Each year, Team Green provides regional support vehicles and highly trained technicians at more than 100 events throughout the United States, offering technical information and assistance to those who race Kawasaki products. Kawasaki also offers a comprehensive contingency program for amateur and professional riders who place well at designated events.


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