Racers are a funny breed that usually fall into one of two categories. The first only care about the act of riding. On or off the track, their thoughts are focused on themselves and what they can do to be better riders. The second kind of racers derive as much fun out of crafting the machinery they race as they do from riding. For them, construction and creativity are as important as the physical activity. Cedric Smith, whose Hayabusa-powered GSX-R750 appeared in the June 2001 issue of Sport Rider, falls into the latter classification.
After racing a Gixxer 750 for a couple years, Smith tried racing a stock GS500 in 1991 and discovered he liked how light and flickable the bike was. In fact, Smith liked the GS so much, he stopped racing his 750 to concentrate on the Lightweight Twins class. Being an incessant tinkerer, Smith happened to have his GS apart at the same time he was working on a GSX-R750 at the shop where he was employed. He didn't see any harm in laying the 750's head gasket on the GS's block-just to see. Well, what do you know? Everything matched up almost perfectly. The journey had begun.
This front end should look familiar since it is a stock GSX-R750 unit. The wheel is a PM Chicane. The fairing is more sultry carbon-fiber. | 
The braided steel hose exiting the head drains the excess oil back into the bottom end. Look for a matching hose on the right side of the engine. | 
Immediately behind the banana bend to the swinger, the rear disc can also double as a cheese grater. The pipe is hand-constructed titanium, and the bodywork is carbon-fiber. Sexy stuff. |
Off-the-shelf parts...well, sorta
Not surprisingly, Smith had friends in the 750 class. So, when a buddy fragged his superbike, Smith took the damaged, but nicely ported, polished, big-valved 1989 GSX-R head (modified by Kelly Roberts at Racing Engine Components in Texas), cut off the two outside cylinders and mounted the remainder onto his GS. Next, he bolted some plates on the end of the engine and was ready to rock. But Smith didn't stop there. The fancy head needed some hefty displacement to feed. To that end he ordered a set of Cosworth 85mm pistons which would normally find their way into a GSX-R1340 kit. Carillo rods made the connection to the OE GS crank. Smith said he chose all these standard parts so that when something failed, he wouldn't have to wait for custom replacements. Still, he had to delve into some specialized items, like Megacycle cams with custom lobes.
Just because Smith wanted to use readily available parts doesn't mean he wasn't thinking outside of the box. A quick look at the bottom of the engine reveals the finned housing for a secondary oil pump, which is driven off the output shaft on the countershaft sprocket side of the engine. Yep, he made sure the expensive head got plenty of lubricant at speed. Said Smith, "There's tons of room in the bottom end for the pump." To handle the extra oil flowing down from the head, he fabricated drain back tubes on either side of the engine to move the oil to the bottom end.
Don't think that this GS650 project was a slam dunk. It suffered quite a few growing pains. The most prevalent was a propensity to break crankshafts. The OE crank simply wasn't designed for the forces the big pistons were putting out. About three times per year, Smith had to replace the motor's shattered backbone. In desperation, he mounted a fluid damper to control the crank's harmonic vibrations. Although the time between failures lengthened, Smith "got tired of throwing cranks at the thing." Not to mention the cases previous crank failures occasionally took with them. Smith turned to Moldex for a billet steel crank with bigger diameter journals. Since the fluid damper was paid for, he mounted it to the monster crank. Now, he's managed more than four seasons without a failure.
The rest of the equation
The remainder of the power output comes courtesy of a pair of Keihin 39mm CRs and ram air. Since Smith didn't want to go through all the R&D required to pressurize both the airbox and float bowls, he simply put the entire carburetor assembly inside the airbox. The manly powerplant exhales through a handmade titanium exhaust system that weighs in at a mere three pounds-including the canisters and packing! This phenomenal weight savings was achieved through the judicious use of some ultra-thin Boeing surplus Ti tubing. The system's cost was only $18-plus 50 hours of labor.
An RGV250 swingarm holds the Performance Machine wheel in line. Note the hand-crafted, lightweight aluminum sub-frame supporting the rear section. | 
Compared to the left side, the engine's right side is relatively mundane...until you notice the pressurized airbox and special head. Any guesses what CSXR stands for? | 
Trickery abounds! From the auxiliary oil pump on the bottom to the tiny battery tucked just rearward to the fluid damper mounted to the end of the crank, this GS struts its stuff. |
The stock ignition powers a set of Dyna coils. The OE GS500 clutch basket holds a set of Barnett Kevlar plates that last half a season, even with the beefed up power delivery. The constant-loss electrical system is powered by a small battery tucked under the countershaft. Although the GS500's frame is fairly stout, the rest of the stock rolling gear reveals the bike's bargain roots. Not wanting the increased power to turn this bike into a flexing, wobbling beast, Smith grafted a 1991 GSX-R750 front end to the frame and an RGV250 swingarm with a Fox shock in the rear. To these stiffer pieces, a set of Performance Machine Chicane aluminum wheels took up residence. Dunlop slicks keep the shiny side up.
The bodywork is all carbon-fiber, consisting of an RF900 fairing and a TZ tailsection. The fiberglass tank tips the scales seven pounds less than stock. Smith says the whole shebang weighs just 320 pounds with enough gas to start the engine.
Smith's efforts in constructing the GS650 paid off for several years by allowing him to dominate the Lightweight Twins class in Washington Motorcycle Roadracers Association's events. That is until the SV650 made its debut. Although the newer Suzukis may have taken the crown, we're certain none of the competition display the creativity and technical expertise Smith has wrapped up in his CSXR. Now, you need to figure out what those letters stand for.
This story was originally published in the October, 2001 issue of Sport Rider.