Yoshimura Dr-Z450sm

YOSHIMURA DR-Z450SM

A Schwantz Replica that trumps Revvin Kevin's racer

YOSHIMURA RACE SHOP HOPES TO HOT-ROD MORE THAN MAT MLADINwannabe GSX-Rs. Yoshimura R&D of America’s new partsand-services division is also selling hop-up engine and chassis components for the dual-purpose DR-Z400S and supermotoinspired DR-Z400SM.

The Yoshimura-modified DR-Z450SM pictured here is an evolution of the machine that 1993 500cc World Champion Kevin Schwantz raced during the early days of the AMA Pro Supermoto Championship. Schwantz supported the revived sport both as a competitor and a member of the AMA Pro Racing board. He viewed the series as an opportunity for dirttrackers, motocrossers and roadracers alike to compete against each other at new, unique urban venues without the “ton of funding” often associated with other forms of top-level racing.

Starting point for Schwantz’s original racebike was an offroad-only DR-Z400 (13 pounds lighter than the later electricstart E-model). A bored-and-stroked 450cc engine package had been developed several years earlier with the help of four-time AMA Motocross Champion Mike Kiedrowski, among others, in the AMA Grand National Cross Country and West Coast WORCS series. The latest version of that kit ($2695) consists of a 92mm (plus 2mm) forged aluminum piston, 5mm-stroked crankshaft, bored and Nikasil-plated cylinder, billet camshafts, high-rpm ignition box, heavy-duty clutch, plus head and base gaskets. Yoshimura Japan designed the special Mikuni MJN 40mm flat-slide pumper carburetor ($1170). Schwantz also raced a prototype of the low-mount, RS4 “twice pipes” exhaust system ($1049) now in production. Peak output, according to Yoshimura, is 54 horsepower and 36 foot-pounds of torque, up from 32 hp and 25 ft.-lb. stock.

Schwantz prefers an RM-Z450 for motocross, but he feels the DR-Z was a better choice for supermoto. “It’s hard to pinpoint a difference between the two engines because Yosh did a good job getting a bit more than 50 horsepower from the DR-Z in the 450cc configuration,” he said. “The biggest thing I noticed is how much smaller and lighter the RM-Z engine feels in the new chassis. But the RM-Z, with its aluminum chassis, was just that much more rigid. The DR-Z, with its heavier steel-tube frame, had a bit more flex. That made it nicer to ride on pavement.” While Schwantz’s racebike was equipped with Öhlins suspension and rolled on hand-cut 16.5-inch Michelin slicks, Yoshimura’s catalog creation is fitted with Showa suspenders modified by Factory Connection and 17-inch DOT Dunlops.

Other differences? Suzuki accessory bodywork, the combination fairing/front fender and sculpted sidepanels in particular, gives this DR-Z a look of its own. The custom “Low-Boy” IMS gas tank-another Kiedrowski holdover-carries an even 3 gallons of fuel, .4 more than stock. A 320mm Braking front rotor is actuated by a Braking 16mm radial front master cylinder and Braking Supermoto caliper with dual 32mm pistons. A 220mm Braking rear rotor is pinched by the stock single-pot Nissin caliper.

Highlight of Schwantz’s supermoto career was winning the Copper Mountain, Colorado, round of the AMA series in 2003, in which he topped fellow racing greats Scott Russell, Jeff Ward and Jeremy McGrath. Curiously, Schwantz didn’t favor the tail-swung-out corner-entrance riding style used by many supermoto racers.

“When I got the back of my bike hung out, ass beside the front, I wasn’t able to skid the back wheel to a stop as efficiently as when I had the front end properly weighted,” he said. “I may not have had the exit speed that I needed, but I was able to get the bike into the corner better.”

Schwantz’s interest in supermoto began to wane with the introduction of steel jump ramps. “I envisioned more of a midEighties Superbikers-type course,” he said, “with a TT jump, a dirt-track corner, a roadrace corner, maybe a rhythm section but not frickin’ steel ramps!”

Lump-in-the-throat leaps aside, Schwantz has good memories of his supermoto racing. “The DR-Z wasn’t the fastest thing out there,” he admitted, “but I felt that if I got everything right, or even close, I could run with just about anybody.”

Now, thanks to Yoshimura, you can, too.

Matthew Miles