Imagine if you could significantly improve both the acceleration and fuel efficiency of your Corvette without even touching the engine. In theory, the approach is fairly simple: Divvy up the powerband with a close-ratio, semi-automatic, eight-speed gearset. This would give the car much more torque and horsepower through the gears, since the engine would drop only half the rpm on each shiftùand there'd still be a top gear with overdrive for low-rpm, long-range cruising.
In practice, however, the realities of corporate politics ended up stifling this significant performance modification for the C5. Even so, it serves as an intriguing behind-the-scenes story of a technological groundbreaker, one that dramatically demonstrates what can be done to optimize the power delivery of not only Corvettes, but of restomods and muscle cars as well.
To set the stage for this insider account, look back to the era of the C4 Callaway Vettes. Those twin-turbo models had way too much power for the factory drivetrain to handle, so Hydramatic supplied a stouter Turbo-400 trans with a Gear Vendors overdrive.
For those not familiar with Gear Vendors, this company is well known in the muscle-car ranks for enhancing those vehicles' crude-but-stout transmissions with bolt-on overdrive systems.
Truck and RV enthusiasts use gear splitters as well, but mostly for lowering revs at cruising speed for better fuel economy and reduced engine wear. (For instance, one of this author's personal vehicles is a one-ton diesel dualie, and it runs down the highway at 70 mph while turning only 1,800 rpm!)
Getting back to Corvettes, while Gear Vendors makes aftermarket upgrades for earlier models, in 2002 company president Rick Johnson and Jon Moss (GM's special projects manager at the time) hatched an idea to apply this versatile technology to a C5. Not one to miss a potential business opportunity, Johnson figured this project car might lead to a long-term contract for an OEM option using Gear Vendors products.
Looking to debut the car at the SEMA show, which was only a few months down the road, he prevailed upon Bob Kern of GM to supply Gear Vendors with a new C5. Kern obliged, also providing extra torque tubes and transmission assemblies for mockup and engineering work.
Gear Vendors received an Electron Blue automatic coupe and began making the components. The car's drivetrain layout meant that the overdrive would need to be located directly behind the engine, a significant departure from the company's typical bolt-on transmission arrangement. As a result, there were a number of parts to design and fab.
It took about 30 Gear Vendors employees working feverishly to engineer, test, and install the new systems in the Corvette over the next five months. They came through in the nick of time, finishing by the October 31 deadline, and Johnson delivered the car to the Las Vegas convention center so Moss and GM Performance's Mark McPhail could do some hands-on testing. Both were elated with the car, comparing it to driving an F1 car in a videogame: "Just too much fun!" was the expression they used.
Why so? Comparing the stock and Gear Vendors drivetrain configurations is telling. When in factory form, the C5's 4L60E four-speed has only two underdrive ratios, plus a Third-gear direct drive and a Fourth-gear overdrive. With the gear splitter, it now had four close ratios of underdrive, a direct drive, and two overdrive gears.
In addition, all those extra gears were available at the push of a MasterShift paddle shifter mounted on the steering wheel. This trick setup uses Gear Vendors programming information to make a truly versatile dual-paddle, two-button system. With the paddles you can pull the right side for close-ratio upshifts through eight speeds and down through the same on the left. The button on the front of the paddle allows for stock four-speed wide ratio changes as well as a stock Drive mode. Virtually any car with a Gear Vendors unit can make use of the system.
As noted at the outset, translating all these extra choices into the driving experience means the car has much more power on demand as you work your way through the gears, since the engine drops only half as many revs on shifts. So rather than experiencing a precipitous "gear gap" between each shift (anywhere from 30 to 47 percent), with the Gear Vendors unit it's largely between 10 and 22 percent.
In other words, what you notice when driving is a switchblade-quick shifting experience. You actually enjoy hitting a series of stoplights just so you can accelerate through the gears again. And fast corners on two-lane blacktop feel really racy, with just the right gear always available for good braking into the turns and acceleration out. It can make an average driver much better, and a good one possibly great.
Add to that a significant improvement in fuel economy. Although Gear Vendors switched the differential gear to a Unitrax 3.90:1 (stock was 3.15) to enable a monster launch, in top gear with the overdrive, it's as if the car has a 3.04 rear cog, which improves mileage by five percent in cruise mode.
The shorter gear also increases torque multiplication by 23.8 percent, the final result being a 4-12 percent improvement in virtually all acceleration criteria, while also achieving gains in both city and highway mileage. Overall, the package met all of its objectives and was a great success at SEMA, where it took home a Best Engineering Award.
Summing it up, Moss noted that, "The eight-speed semi-automatic was a ball to driveùa real enthusiast's transmission with the tight ratio spread that makes [it] a real joy through the gears, and yet still cruised down the road with low rpm when that was what you wanted. You could see this one car pleasing both the automatic- and manual-transmission guys."
Given the success of the project, why didn't it ever become a production-car option on the Corvette? Not for lack of effort or investment, that's for sure. During the months leading up to SEMA, Gear Vendors had been given OE proprietary pricing on the torque tubes, driveshafts, lower-durometer rubbers, and bigger components of the manual car from GM supplier Unidrive in Australia. The orders had been placed for a 1,000-unit run, but just after the show, Johnson got word that the order had been cancelled and GM would no longer allow the supplier to deal with Gear Vendors directly.
"What the hell?" was the obvious question. Well, unbeknownst to Gear Vendors during the project build, Hydramatic was working on the six-speed automatic for the upcoming C6 Corvette. Johnson surmises that GM felt it was counterproductive to bring out an eight-speed, limited-edition gear setup ahead of its own factory offering.
Looking back on the whole deal, how does Johnson view it? "My experience with GM [was like] shaking hands with a friendly dinosaur 100 times your size," he relates. "When the giant turns around to shake hands with someone else, his tail wipes you off the face of the planet and he doesn't even know it."
But why not offer it as an aftermarket upgrade for the C5? With a target price of $4,000 for the kit, the project became impossible because all the beefed-up GM hardware that was to be included would now cost more than $3,500 on its own.
Alas, within two short months of finishing the project, the entire enterprise was mothballed. How expensive was it for all the engineering, testing, prototypes, tooling, manuals and press books, and more? "It was up there, something near a million," Johnson admits with a wince, trying to remain philosophical. "I really try not to think about itùjust a good lesson."
What remains is a car that's a complete blast to drive. And there's some satisfaction to be had when pedestrians on the sidewalk and drivers in the next lane yell out (after spotting the "8-Speed" badging on the car), "Is that really an eight-speed?" It sure is, as they soon learn when the car accelerates away through twice the typical allotment of gears.
Other eye-catching mods include a set of Colorado Custom Slater wheels, specially made for desired offset and wrapped in Goodyear Eagle F1 rubber (265/35ZR18 front, and 275/35ZR19 rear). The car was lowered by just over an inch using the factory adjustable leaf settings to give it a more aggressive stance.
What are Johnson's plans for the car? "I drive it to work once in a while or out to dinner, but try not to put many miles on it so it can stay pretty," he laughs. "I would like to see it go into a Corvette or GM collection where it will be preserved."
The eight-speed C5 is fully documented and DOT legal, so unlike some one-offs, this one loves to be driven. It's an interesting piece of history, and while GM may someday offer its own eight-speed Corvette, this one will always be the first.