Suzuki Casts Off The Carburetor And Launches The First Mass-Produced, Fuel-Injected Motocrosser
The unforgiving motocross environment demands simplicity and durability, factors that have so far kept fuel systems locked in the last millennium. Until now, that is: Suzuki designed a fresh electronic fuel-injection system for its latest RM-Z450, based on GSX-R streetbike technology, which performs better than a carb and can still take a beating.
The first mass-produced, fuel-injected Mxer is newsworthy enough, but the 2008 RM-Z450 is a completely new motorcycle with a redesigned frame, upgraded suspension and a list of other engine and transmission upgrades. How does it work on the track?
First, the EFI system gets smooth, progressive power from the 449cc, four-stroke single. Slam the throttle open and the motor responds instantly, without complaint. Rev its brains out and the RM never falters, it just immediately barks, no matter what.
The bark-to-bite ratio is right on. Meatier low- and midrange power output (the result of higher compression, a reworked cylinder head and revised cam timing) works better at slow speeds. A rising-rate throttle body linkage that opens the butterfly more rapidly as you approach wide-open throttle helps build power in a way that greatly enhances traction. A properly spaced five-speed tranny replaces the track-only four-speed of the past, giving the bike legs to carry this new power.
Peak horsepower numbers are less important on-track than power that builds smoothly to maintain traction. The RM-Z delivers smooth power from the first crack of the throttle, with good thrust across the rev range. It can be ridden easily or aggressively, though the '08 runs through the revs quicker than we'd like. The easy solution? Shift early and use the clutch to keep the motor in the meat of the power. Don't worry about bogging or hesitation out of the corners running a gear high-EFI makes lugging easy.
Instant throttle response and ample traction make the RM-Z a capable partner in deep ruts or tighter, harder-packed tracks. The heavier flywheel required to charge the uprated electrical system aids that buttery flow of juice to the rear tire, which brings us to the downside: EFI requires lots of electricity to run the fuel pump, injector and computer. And since there's no battery, the RM-Z's electrical system has been beefed up to make more juice-at the cost of more crank inertia.
A stronger, 18-pin magneto handles the load with more magnets pulling against your leg, making the RM-Z a bear to kick over at times. Come up on compression in the wrong spot, with the magnets all lined up, and you're in for a workout. It takes a few taps of the boot to budge the kickstart lever, and then it's business as usual. This doesn't happen all the time, but it can-and probably will.
Bodywork is new for '08, and suits the now-moreaggressive character.
The new RM-Z450 shows Suzuki did its homework in the handling and chassis department. The best way to describe the bike is "planted." Earthbound, the RM-Z has a solid, super-balanced feel, biting into corners with confidence and lofting the front wheel on the way out. It's quick turning, like a traditional Suzuki, and at the stock settings (sag in the 100-105mm range) carries itself all the way through an apex without blowing through the suspension stroke, unlike past RM-Zs. Braking bumps disappear, along with small chops and square edges.
It bottoms too easily, but doesn't feel like the heaviest 450 (claimed dry weight is 224 pounds) out there, especially not in the air. Airborne, the RM-Z450 baffles you with a superlight, very un-450-like feel. The bike is almost feathery in the air, flickable and easy to maneuver-an unexpected complement to its planted character displayed on terra firma.
The '08 RM-Z is certainly a contender, with a confident chassis, solid suspension and some of the most usable power we've experienced. yank the throttle and you'd never know there's not a perfectly tuned carb under the tank. It's an excellent bike for anyone who hates jets, and it proves-at last-that fuel injection works in the dirt.
Suzuki's top MXer bins its carb in favor of electronic fuel injection and gets a fifth gear too.
Hard-core, big-bore four strokes: Honda's CRF450R, Kawasaki's KX450F, KTM's 450 SX-F and yamaha's yZ450F.
|Price: ||$7199 |
|Engine type: ||l-c single |
|Valve train: ||DOHC, 4V |
|Displacement: ||449cc |
|Bore x stroke: ||96.0 x 62.1mm |
|Compression: ||12.2:1 |
|Fuel system: ||Keihin EFI |
|Clutch: ||Wet, multi-plate |
|Transmission: ||5-speed |
|Claimed horsepower: ||na |
|Claimed torque: ||na |
|Frame: ||Aluminum double-cradle |
|Front suspension: ||Showa inverted fork, adjustable for spring preload, rebound and compression damping |
|Rear suspension: ||Single Showa shock, adjustable for spring preload, rebound and compression damping |
|Front brake: ||Two-piston Nissin caliper, 250mm wave-cut disc |
|Rear brake: ||Single-piston Nissin caliper, 240mm wave-cut disc |
|Front tire: ||90/100-21 Bridgestone M403 |
|Rear tire: ||120/90-19 Bridgestone M404 |
|Rake/trail: ||25/30 in. |
|Seat height: ||37.6 in. |
|Wheelbase: ||58.3 in. |
|Fuel capacity: ||1.6 gal. |
|Claimed dry weight: ||224 lbs. |
|Color: ||Yellow |
|Available: ||Now |
|Warranty: ||na |
Contact: American Suzuki
3251 E. Imperial Highway
Brea, CA 92622
Agile in the air and solid on the ground, the easyriding RM-Z proves EFI works in the dirt too.