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2005 4-Stroke MX Shootout

Sunday, June 12, 2005

To decide on the best MX 4-stroke, we had to take it outside, so we could determine the worthiness of these three high-performance machines.
Over the past few years motocross technology has come on like gangbusters. Of course, Yamaha sparked the competition-based thumper revolution in 1998 when Doug Henry legitimized the four-stroke by winning the Outdoor Nationals aboard a YZ400F.

Over the next few years, Yamaha would go on to develop the YZ426F and then YZ450F with little competition from the other Japanese manufacturers. However, Honda soon entered the high-po four-stroke motocross market when it introduced the CRF450R. It didn't take long before Ricky Carmichael put the official stamp of approval on 4-stroke technology in 2004 when he piloted the CRF450R to a perfect AMA Motocross season, something that's only been achieved once before (by RC, of course). Now it seems, a rider is at a disadvantage if they are on anything but a fire-breathing four-stroke.

Suzuki is the latest player to enter the competition 4-stroke market. While the RM-Z450 didn't hit dealer showroom floors at the exact moment originally slated, the RM-Z did arrive and Suzuki picked a great year to do so. Whether it was luck or just good planning, Suzuki opted to introduce the RM-Z in a year when Honda and Yamaha did little to change their respective machines.

This trio joins long-time four-stroke specialist, KTM and Husqvarna as the leaders in the market, however we were unable to procure a bike from either European manufacturer for our shootout and we will have to wait until next year. We'll keep our fingers crossed and hopefully for 2006 we'll be able to make it a six-bike competition - don't forget the arrival of the KX450F.

For this test we opted to combine our track and trail notes and then designate an overall winner with a heavy emphasis on track performance, since that's what this trio was designed for. We split time between our local MX track, Rogue Valley Motocross Park in Medford, OR, and on the rugged trails of John's Peak, where we could determine the worthiness of these three high-performance machines in less WFO areas.

Remarkably, the internal components on this trio are quite similar, but a closer look reveals small philosophical differences in the respective engines. Bore and stroke are nearly identical on all three, as is compression ratio. However, Suzuki opts to utilize the dual overhead-cam configuration with four valves, while Yamaha utilizes five titanium valves in a DOHC configuration. Honda, always looking to do something different, actuates four valves with its patented Unicam configuration, which is designed to reduced overall engine height, keeping the center of gravity as low as possible.

For this test we opted to combine our track and trail notes and then designate an overall winner with a heavy emphasis on track performance  since that s what this trio was designed for.
Kawasaki was absent for our shootout, but will likely be present for our 2006 four-stroke MX extravaganza.
The internal components come together to form a trio of 449cc liquid-cooled, 4-stroke, single-cylinder engines. Not one mill seems to have any significant design advantage over the others. However, somehow the engineers of each respective manufacturer managed to give their bike a distinctive personality. One was louder and more obnoxious than the rest: the YZ450F.

Twist the throttle and the engine roars to life like a exorcised demon. Stay on the throttle and the YZ keeps dishing out power by the fistful. In fact, the engine was routinely rated with 10s on our scorecard, and while that seems to make the YZ the horsepower winner, it only tells one side of the tuning story. It offers brute strength but it comes at a price, as it revs through the middle of the powerband rather quickly and reaches the top of the rev range in a hurry. The bottom line on the YZ450F is that it hits like Chuck Liddell but lacks some of the refinement and stamina of Randy Couture.

"The YZ450F would probably benefit from more flywheel weight," said Mikey Horban, one of our fastest testers. "It hits really hard off the bottom, but almost too hard. It's nice to have a lot of power, but you want it to be manageable and smooth."

The YZ's low-end prowess was even more noticeable on the trails of John's Peak. Ride it in first and you'll probably end up on your keester, especially on steep hills. A more demure hit on the bottom would ultimately make it a better machine to ride in the woods.


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