Grass-Roots Racebike

Grass-Roots Racebike

From showroom to Suzuki Cup

THERE’S NO SUCH THING AS A box-stock racebike, not if you want to hang with the frontrunners in Suzuki Cup racing. Rules allow a certain number of alterations from stock, and Cycle World took advantage of them when building our Project GSX-R600.

Tom Houseworth of Houseworth Power Service was enlisted to prepare our Suzuki’s engine. Houseworth’s Supersport motor prep included blueprinting the bottom end; boring the cylinder to 1mm oversize; a racing valve job; slotting the cam sprockets, timing the cams; and installing a Dyno-Jet carburetor kit. Labor came to $1200 plus $400 for Suzuki pistons, rings and gaskets. A Kerker Kseries exhaust system capped off the motor work.

With cam timing set for the tighter circuits, the engine gained as much as 20 horsepower over stock in the midrange, with peak power of 86 horsepower at 9500 rpm-16 more than the stocker at the same rpm. The trade-off was significantly less power on top, down some 15 horsepower at 12,000 rpm. With cam timing degreed to better suit ultra-fast Road Atlanta for the Cup Final, we got peak power of 85.5 horsepower at 1 1,500 rpm, with a 4 to 7 horsepower increase over stock at all revs above 7000 rpm.

In both cam-timing configurations, quarter-mile performance was nearly identical, with a best run of 1 1.20 seconds at 123.45 mph. That’s considerably better than the stock GSXR600’s 11.92-second/l 14.79-mph showing, though it should be noted that the racebike, shorn of all street equipment, was 35 pounds lighter than stock.

Replacing the stock 530 chain and sprockets with 520 components gave us a reduction in unsprung weight and drivetrain drag. We fitted RK’s GY520XO gold sprint-racing chain, which easily handled five weekends of racing and dragstrip testing with no stretching after initial break-in. Armed with a selection of 13/14/15tooth countershaft sprockets and 44/45/46-tooth rear sprockets from Sprocket Specialists, we had a wide range of final gear ratios. The company’s Titan Tough aluminum rear sprockets showed no visible wear after hundreds of racetrack miles.

Fox Factory supplied a Twin-Clicker Racing Shox to insure consistent damping under racing conditions. The remote-reservoir shock has adjustable spring preload, compression and rebound damping; it also features a threaded lower clevis for altering rear ride height, so the GSX-R’s steering could be quickened if needed, along with increasing its already superb cornering clearance.

To fend off tankslappers, especially with the rear ride height raised, we fitted a Storz GCB steering-damper kit, which retained full lock-to-lock steering. This was a simple bolt-on installation, and the GCB damper is beautifully constructed, but on a very hot day at Willow Springs Raceway, it began to seize, causing the bike to weave. The damper was sent to Storz for inspection and a part was found to be out of tolerance. Once corrected, the damper performed flawlessly for the rest of the season, including two more late-summer scorchers at Las Vegas and Phoenix.

Brakes were upgraded with Galfer Kevlar pads and teflon steel-braided lines. With these in place, brake performance was excellent, remaining firm and fade free, though four race weekends are the outside limit before the pads need replacing.

In roadracing, tires are all-important and that’s an area where the GSX-R’s 5.5-inch rear wheel gives it an edge over the competition. The Suzuki is the only 600 that can run the new Dunlop D364 Sport Radial, which is available in a 180/55ZR17 size only. Though expensive, the D364 totally dominated AMA/CCS 750ec supersport racing this year, and I’ve never raced on a better DOT tire. Up front, we used a Dunlop Sportmax GP Radial in a 120/70ZR17 size,

which provided excellent grip and steering characteristics.

Add up the costs of bike, parts and services, and figure on spending about $10,000 to bring a competitive GSX-R600 to the grid. The good part is that Suzuki will gladly reimburse you for good showings at the racetrack. Just ask Kurt Hall. Don Canet

SUPPLIERS

Dunlop Tire Corp. R0. Box 1109 Buffalo, NY 14240 800/828-7428 Rear D364 Sport: $290 Front Sportmax GP: $144

Fox Factory, Inc. 3641 Charter Park Dr. San Jose, CA 95136 408/269-9200 Twin Clicker damper: $495

Giocar America Inc. 104 San Federico Ave. Santa Barbara, CA 93111 805/967-2726 Galfer brake pads: $33/pair Brake lines: $85 front

Houseworth Power Service 205 W. Harbor Blvd. Santa Ana, CA 92703 714/554-1486 Engine work: $1200

Kerker/SuperTrapp 3910 Seaport Blvd. West Sacramento, CA 95691 916/372-5000 K-Series exhaust system: $380

FTM & Associates 1240 Rancho Encinitas Dr. Encinitas, CA 92024 619/756-9461 RK racing chain: $284

Sprocket Specialists Rear sprockets (3): $142 Countershaft sprokets (3): $56.50 Available from local dealers

Storz Performance 1445 Donlon St., #18 Ventura, CA 93003 805/654-8816 GCB steering-damper: $225