SUZUKI 440 RACE EDITION
The Suzuki DRZ isn’t a motocross bike. Just ask anyone at Suzuki. But if you ask us, it could be–all the parts are there. Could the DRZ be as good as a YZ426? Now there’s a challenge. And we’re never afraid to take on a challenge. For our July issue we started researching the project. We started off with a kick-start version of the Suzuki. It’s ten pounds lighter to start with, weighing in at about 266 with all the lights, kickstands and trail stuff. Then we got down to business with Project DRX.
STAGE ONE: THE BASICS
Before going crazy, we wanted to see how the DRZ would perform with just simple modifications. So we raced it several times with all the enduro junk stripped off, and with exhaust and suspension modifications. The Suzuki’s engine is awesome to start with–it makes more power per decibel than any bike we’ve ever had. But a race bike doesn’t necessarily need to be quiet. So we installed a Yoshimura titanium exhaust system and bumped the main jet up to a 165. Between stripping off the enduro gear and installing the Ti exhaust, the bike lost over ten pounds. That’s about as far as we wanted to go with weight loss, though. It still isn’t as light as a Yamaha, but it’s within a few pounds and that’s close enough.
The seat was a more difficult problem. The reason that it slopes rearward is because of the big, tall fuel tank. Suzuki was trying to smooth out the transition. We figured it would be better to deal with a poorly shaped tank than with a poorly shaped tank [and] a poorly shaped seat. The people at Ceet make new foam that’s lower in the front and taller in the rear. In other words, they made a pocket for the rider to sit in, sort of like an XR.
REPORT CARD #1
We’ll give our stage one project a solid B. The bike became a decent race machine that can win against the best stuff out there. The power delivery was excellent and the suspension was better than we had hoped. But the bike had limitations. First of all, it was still a little down on power. The bike makes great low-end, but in a full-on, corner-to-corner drag race, you don’t need that much torque. You need horsepower, and the Suzuki didn’t have the sheer acceleration to outpull the average 250cc MX bike. The engine had the potential, but the ignition had a low rev ceiling. Just when you thought it was going to make serious holeshot power, the bike started missing.
The obvious next step would be to find a way to make the DRZ rev. At 10,000 rpm the advance curve retards radically. A YZ, on the other hand, keeps going all the way to 11,500 rpm. Unfortunately, Suzuki never built the engine with revs in mind. If you replace the advance curve with one that lets the bike scream, the valve train can’t take it. She’ll blow up. We’re not saying it might blow or could blow. It [will] blow. If you were determined, you could use Ti valves and springs and maybe redesign the buckets and shims, but there’s an easier way to make the bike perform: displacement. As it turns out, the piston construction is very similar to a YZ’s (imagine that!). But the Suzuki has a longer stroke. So if we could stick a YZ426 piston into the DRZ, the resulting displacement would be 436cc.
But more problems: the 426 is a five-valve; the DRZ is a four valve, so the valve pockets are all different. Plus, the DRZ has a larger wrist pin. Luckily the guys at Thumper Racer were way ahead of us. They had already taken a Wiseco piston blank and remachined it to use as a prototype. There’s a dedicated piston in the works. So Thumper sent us a prototype piston and resleeved our cylinder. The result is the DRZ440. With more displacement, the engine won’t need to rev out–it will peak earlier.
With more power, the weak spot is the clutch. Hinson was already making a basket, but no one has beefier springs yet. There are companies out there working on the project; KG clutch factory and Barnett, for example. But nothing yet. All we could do was use the old spark-plug washer trick to increase the preload on each spring by about a millimeter. Luckily, KX500 clutch plates go right into the new bike, so there’s no shortage of plates.
We decided that the clamps should have about 3mm less offset than a stock RM (bringing the measurement to 21.5mm), and R&D guys went to work. In two days they produced a set of clamps that were virtually works of art.
REPORT CARD #2
The proving ground was the White Bros. Four-Stroke World championship at Glen Helen. DB test rider Mark Tilley twisted the throttle in the Pro class (it took about 15 seconds to talk him into it).
As you might expect, the White Bros. race was a sea of Yamahas with a sprinkling of KTMs. It was a horsepower track with tall hills and loose dirt. Tilley would have his work cut out for him. We knew that the Yamahas and KTMs would have more top end and were lighter. We hoped that Project DRX’s torque advantage would pay off somewhere.
Tilley was pumped. ‘I can pull Yamahas on the big hill,’ he reported. We weren’t sure if he was hallucinating, but we smiled and nodded. Since Stage One, the Suzuki had changed a lot, but it was still the same bike with the same rev ceiling. The handling slowed down considerably, and Mark said that it felt a little heavier. The flip side was that the front end got much better traction. As for power, it was more than a match for anything on the track on the bottom. The 440 was a torque monster. On top, it still hit the rev limiter early, and that’s where the Yamahas and KTMs had an advantage. Mark’s strategy was to upshift like a madman and keep the revs low. He’s normally a 125 rider so it certainly didn’t come naturally.