DRZ - Forum

SUZUKI 440 RACE EDITION
6.30.2000


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.

Race Tech revalved the stock suspension and installed heavier springs in both ends. The conventional fork is super soft, but has potential. It isn't that different from Suzuki's last single-chamber RM fork, which was regarded highly in the motocross world. The tubes are even larger than the old RM version, so flex just shouldn't be a problem. Race Tech installed 0.44 kg/mm fork springs along with Gold Valves. In the rear, the revalving was matched to a 5.4 kg/mm spring.
We wanted a few more mods to bring the bike into race trim. The stock riding position is really weird. A super soft seat with a rearward slope makes you slide back. And the stock handlebar position keeps you there. BRP makes the best bargain in the handlebar clamp business--it moves the bars forward about 10mm. That, along with AFAM bars, gets rid of the big, fluffy trail bike feel.

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.
In the handling department, good suspension isn't quite enough. The DRZ was great in turns, but had a tendency to wander slightly in rough straights. Sound familiar? That's the same complaint that many riders have with the RM250 motocrosser.


STAGE TWO: GETTING SERIOUS

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.
Going to the next level in the chassis department was obvious: RM suspension. We started hunting for a set of upside-down forks and found a 2000 RM125 front end. Race Tech did the revalving and bumped the spring rates up to 0.44 kg/mm. The fork clamps were more of a challenge. Stock RM clamps will go right on without trouble. But the offset is much more than stock. That results in less trail and [more] twitchy handling. The bike already felt too twitchy. Steering geometry is a black art, anyway. Almost no one understands it. Years ago, we rode a bike with almost no trail--the fork offset was so great that the front axle was directly over the point at which the steering head center line hit the ground (think it through slowly). The front end wanted to flop from one extreme to the other. When you gave it throttle, the bike wanted to turn. When you let off, it could be straightened out (the opposite of everything normal). So we felt that a decrease in offset was what the Suzuki needed. The only company that would tackle the project was Factory R&D in Orange County. Factory R&D specializes in making lightweight clamps from a scandium/aluminum alloy. It's the only aftermarket clamp that's actually lighter than stock.

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.
In the rear, the stock shock is every bit as sophisticated as an RM shock so there was no reason to swap. We bumped up the spring rate again so the bike would be balanced with the more rigid front end. We finally landed at a 5.6 kg/mm spring. The final touches were a 19-inch rear wheel (an Excel rim with White Bros. RM spokes) and some DSP carbon-fiber goodies.

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.
We were worried about the clutch. The DRZ is a trail bike with a one-finger clutch pull. Now it had at least 10 additional horsepower and a 125 rider at the controls--we figured the clutch would burn out about halfway through the first moto. Surprise! It lasted all the way through the race and still looked great afterward. "I didn't need to clutch it at all! It pulls hard all the way from the bottom."
When the results were posted at the end of the day, there were three different brands of bikes in the top ten. As expected Yamahas won the race and a few KTMs made good showings. But in tenth overall, there was a lonely Suzuki. Mark proved that the Project DRX could run with the fastest four-strokes on earth. That was exactly what we set out to do, so we modestly have to give the project, and Mark an A plus. Is there a Stage Three in the works? Sure--running with the big boys is one thing. But beating them would be even more fun.

PROJECT DRX
Yoshimura pipe ... $669.95
Race Tech fork revalve ... $260
Springs ... $79.99
Race Tech shock revalve ... $235
Spring ...$89.99
BRP top clamp ... $149.95
BRP chain guide ... $69.95
Ceet foam ... $59.95
Ceet Gripper cover ... $69.95
AFAM Handlebar ... $74.99
Thumper Racing 440 kit ... $450
Used RM fork legs ... market
Custom Factory R&D fork clamps ... call
Hinson clutch basket ... $225
DSP fork guards ... $100

CONTACTS
Thumper Racing ...(903) 938-0570
Yoshimura ...(909) 628-4722
Race Tech ... (909) 594-7755
BRP ... (949) 380-1160
Factory R&D ... (949)425-8952
White Bros. ... (714) 692-3404
Hinson ... (909) 946-2942
Ceet ... (760) 599-0111
AFAM ... (714) 379-9040

noch einer mit der geübten rechten Maustaste....

Die müsste es jetzt noch mit translation geben....
das wär klasse.

Rainer