Yoshimura Suzuki DR-Z450SM - The 12 Bikes Of XXXMAS

Throwing The (Wish) Book At A Street-Legal Supermoto

By Ari Henning, Photography by Scott Hoffman

Mention the name Yoshimura and even a knowledgeable enthusiast will think of exhaust systems. That's because most are unaware of the firm's deep roots in racing. From Hideo "Pops" Yoshimura's humble beginnings as an airplane mechanic in Japan, through his inaugural involvement in the 1976 Daytona 200 sponsoring Wes Cooley, to Mat Mladin's domineering exploits in the AMA Superbike Championship, Yoshimura Research & Development has been at the forefront of performance engineering for decades.

That said, the majority of Yosh's race-kit parts have been withheld from the general public, reserved for its factory confidants. Until now: The performance powerhouse recently created the Yoshimura Race Shop, an online storefront that gives public access to the company's complete catalog of parts and services. For racers, hardcore track riders and horsepower junkies, the YRS catalog is the ultimate Christmas wish book.

It's no coincidence that most of the go-fast goodies are for Suzukis, Yoshimura's primary focus for many years. Likewise, it's no surprise that the catalog contains more than a few pages devoted to the DR-Z400SM, the do-it-all, dual-sport-based supermoto that's been a big seller since its debut in 2005. To promote its mind-blowing array of wares, Yoshimura assembled the dream DR-Z shown here, fully loaded with every part in its catalog.

The first thing touched was the motor, fitted with a Big Bore Stroker Kit. Developed in collaboration with Suzuki's off-road racing team, the kit is designed to give the DR-Z some serious stomp, and is the same setup Kevin Schwantz used when he tried his hand at supermoto racing a few years ago. This punches out the bike's 398cc engine to 449cc by way of a 92mm piston (up from 90mm), Nikasil-coated cylinder and a stroked crank with a 5mm offset crankpin. A custom forged-aluminum piston features a repositioned wristpin to accommodate the new connecting-rod angles, and is stronger than stock to withstand dramatically increased piston speeds. The jug work boosts compression to a heady 13.5:1 (up from 11.3:1)-high enough for a significant power gain but still low enough to run on pump gas. Complementing the cylinder work are the billet ST-R high-lift cams and the Racing Igniter ignition module, which extends the ignition curve and raises redline to 11,000 rpm (stock is 10,000).

Also included in the Big Bore kit are heavy-duty clutch plates and springs, necessary to cope with the increased power output. With the clutch apart, the stock basket is swapped for a lighter, stronger, CNC-machined Hinson unit for improved performance and durability. Unfortunately, a slipper clutch is not yet available for the DR-Z, so it takes a deft left hand to back it in.

With the cylinder head removed, skilled hands massage the intake and exhaust ports to Stage One specs. The stock steel valves are replaced with larger titanium poppets that weigh about 40 percent less, permitting the engine to rev to its newfound rev limit quicker without need of stiffer valve springs. Valve guides and seats are replaced with beryllium-copper units (the same stuff used by NASA in rocket nozzles and nose cones). This costly alloy provides the thermal conductivity and hardness needed to keep the valves cool and resist the hammering seating action caused by the cam lobes' aggressive profiles. The DR-Z's hungry maw is fed by a 40mm Mikuni MJN (Multiple Jet Nozzle) flat-slide racing carburetor that offers optimal fuel atomization and supplies gas directly to the center of the air stream. An oversize BCM air filter replaces the stock element.

Tuned and tweaked to the extreme, the YRS-built engine is strong enough to stimulate even the most melancholy motorcyclist's salivary glands. But it doesn't stop there: Check out the RS-4 twin-pipe exhaust, a setup that was previously only available if your name was Schwantz and you were tight with the engineers. This beautiful 1-into-2 system is hand-made from stainless-steel and carbon-fiber and does wonders for the power curve as well as the bike's profile.

As you might expect, the modified motor lays waste to the stocker. Horsepower is up from 32 bhp at 7700 rpm to 53 at 8800, and torque jumps from a respectable 25 lb.-ft. to a whopping 36. Yet even so, in this state of tune the bike can be flogged in the canyons on Saturday, raced on Sunday and still be ridden to work Monday through Friday.

Considering that a supermoto bike as wild as this could only lead to Reckless Riding charges on the street, we took it to the Grange Motor Circuit in Apple Valley, California. The ultra-tight, .8-mile kart track made us roadracers feel like Shamu in the shallow end of the pool, but there wheelies, wheelspin and hacked-out corner entries are the norm.

The Yosh DR-Z truly is an extreme machine, and an entirely different animal than the stocker. Acceleration is instantaneous, sending the front tire skyward while leaving a dark smear with the rear. The motor is fantastic: Power hits like a ton of bricks off the bottom and, rather than peaking, plateaus before running up against the rev-limiter.

Navigating Grange's twisted layout was easy thanks to the DR-Z's upgraded suspension, completely reworked by Factory Connection and featuring a trick, black DLC (Diamond Like Coating) on the fork tubes for reduced friction. Slowing for the hairpin turns requires just one finger on the lever thanks to the Braking radial master cylinder, oversized 320mm wave rotor and caliper. Lighting up the rear tire at corner exits is as easy as twisting the quick-turn throttle, and the exotic isotropic super-finished transmission shifts smoothly while the bike wheelies toward the next turn. Despite its firm suspension settings, the bike still handled jumps well, although hard landings scraped the low-slung exhaust's mid-pipe.

The Yosh DR-Z's main limiting factor is its astronomical build price. All things considered, it's still a $20,000 single. And it's way more than anyone would ever need or want- unless you're a top-level racer or an eager enthusiast penning your plea to the big guy at the North Pole.

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