For 2011 Kawasaki has reworked the KX450F. The latest open-class KX motorcycle starts with the Supercross race-winning 449cc DOHC four-stroke single housed in an aluminum frame.
Last year, the KX450F featured a number of engine refinements, including the first ever production use of a bridged-box bottom piston, revised cam timing for better mid- and top-end performance and a reinforced cylinder sleeve and crankcase for durability.
This year there is more. The bridged-box bottom piston shape, for instance, has been modified to meld with the upgraded, higher-volume muffler, which is quieter.
The Kawasaki engine has 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.
The KX450F Digital Fuel Injection (DFI) automatically adjusts to suit track and climate conditions, and offers stable fuel metering even when landing motocross jumps.
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 60-micron fuel particles for smoother engine response throughout the rpm range. The ECU has been tweaked to provide a hotter and longer-duration spark for improved low-rpm response.
Changes in the chassis department include 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.
The 2011 Kawasaki KX450F 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 Kawasaki Uni-Trak rear suspension linkage below the swingarm provides a long rear suspension stroke and facilitates precise shock tuning.
Complementing the Kawasaki KX 450 F motocross 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 2011 Kawasaki KX450F 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.
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