Yamaha YFZ450R
In 2004, Yamaha took the sport ATV world by storm with the release of the YFZ450. This was the first true sport-performance ATV in its class that featured technology straight from the popular YZ-F dirt bike. Soon after the debut, many other manufacturers joined the bandwagon with their own versions of high-performance 450cc-based machines and tried to compete for this extremely popular market share. Not only did this machine attract many of the top ATV racers in the nation, but it also drew a huge customer base that wanted a high-performance machine. Since its release, it has been the hottest-selling sport-performance ATV on the market.
Trying to one-up the YFZ450, other manufacturers have produced performance sport ATVs with more racing-inspired design by increasing the width to 50 inches and adding race-specific 18-inch-tall rear tires. Sure, these machines were great for the track, but for those riders who didn't want a motocross-specific quad, they were left longing for more. This is where the engineers at Yamaha have significantly stepped things up with once again another new groundbreaking machine for 2009. After extensive market research, they learned that the average YFZ customer wanted race technology but very few of them actually raced their machines. The customers wanted an aggressive trail machine with all the performance of a pro-level racer while still remaining affordable. Yamaha took all of this feedback back to the drawing board, and what it came up with is the all-new 2009 YFZ450R.
The Specifics
Typically when a company comes out with a new-and-improved unit, there are subtle changes in suspension, engine and "bold new graphics." Such is not the case with the YFZ450R. The first and most noticeable differences to the eye are the engine and frame. The new frame is made from cast aluminum that is 15 percent lighter than the old steel frame and, with its zero weld design, is extremely strong. To keep a low center of gravity by having the engine mounted as low as possible, the only parts of the frame that remained steel were the lower frame rails. This resulted in a crank position that was 6.4mm lower than the competition's engine placement with similar frame design. The three-piece sectional frame and removable subframe are very similar to the Raptor 700 design, which has already proven itself very durable in any conditions.
Stuffed into the aluminum frame sits the technical masterpiece that is the YFZ450R's new fuel-injected engine. With the old and new engines side by side, it is easy to see that the YFZ450Rs powerplant is new from the ground up. The process of making power starts at the 42mm Mikuni throttle body which houses a 12-hole Denso fuel injector. Here both air and fuel are mixed and sent to the newly designed cylinder head which has a new intake port shape for better unrestricted fuel delivery into the cylinder. Also inside the head are the camshafts, which have new profiles for increased overall performance and power.
The lower end of the engine has cases that are stronger than the previous model and house a new crankshaft that has been beefed up as well for increased durability. The connecting rod features a lower end bearing that has a 2mm larger ID and 3mm larger OD and is 2mm thicker in that area as well. In conjunction with the crankshaft, the engine counterbalancer has been improved for reduced engine vibration and reliability. The finishing touches in the bottom end are the new gear ratios throughout the transmission and an internal oil tank, which makes for a simplified design and more compact centralized engine mass that helps improve the overall handling of the machine.
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