"A lot of Corvettes suffer...
"A lot of Corvettes suffer from bad clutch fluid, due to the seals. It's an inherent problem, even in low mileage cars-this one has 8,500 miles," says Tanner. Synthetic fluid offers a higher boiling point, which helps for open-track days because of the lines run by the headers. The downside is that synthetics are bad for the seals. Tanner therefore recommends using the factory fluid and changing it whenever it gets really dirty.
GM's LS-series small-block engines pack a powerful punch in their various forms, from the base Vette's LS3 to the king LS9. Better still, increasing horsepower and torque in any LS platform is almost too easy. The market offers dozens of cylinder heads, camshafts, intake manifolds, exhaust mods, fortified internals, nitrous oxide, and several types of supercharger and turbocharger systems. As a result, a street-driven 1,000-rwhp Vette is no longer a topic for science-fiction movies. The unfortunate reality is that drivetrain durability under such extreme conditions will unavoidably suffer. Thankfully, racing technology has trickled down to the streets, and the latest dual-disc clutch systems can handle almost anything an LS engine is capable of throwing at it.
The dual-disc clutch was born from the high demands in certain racing arenas, particularly circle-track competition. By spreading the clamping force over two clutch discs, these units provide superior holding power without significantly increasing pedal feel. Dual-disc clutch technology spread to other racing disciplines and eventually found its way to the street crowd, albeit with a few mods to make these setups friendlier in everyday use. (While chatter plagued some early aftermarket dual-disc clutches, most companies have since modified their designs to provide a silk-smooth feel.)
The trickle-down effect continued, and last year the ZR1 Corvette brought dual-disc clutch technology to the GM parts bin. Realizing that none of their existing single-disc units could properly harness the LS9's 604 lb-ft of torque, GM engineers were forced to get creative. Their solution came in the form of a dual-disc system with twin 260mm discs. (To put that into perspective, the C6 Z06 utilizes a single 290mm disc to back the naturally aspirated LS7.)

The old single-disc is re...

The old single-disc is removed.

The ZR1 clutch is stacked,...

The ZR1 clutch is stacked, and a separator plate (or floater cage and plate) goes between the two discs.

This yellow Z06 didn't receive...

This yellow Z06 didn't receive the ZR1 clutch combination, but its low 10-second performance certainly makes it a candidate for one.

Our test C6 was slated to...

Our test C6 was slated to receive an Edelbrock E-Force TVS supercharger. Redline Motorsports decided to add a ZR1 clutch in preparation for the new blower. The Redline crew begins by liberating the rearend and cradle, the transmission, the torque-tube, the headers, and the X crossover.

The rear suspension cradle...

The rear suspension cradle is removed to gain access to the rearend.
We've watched several high-profile ZR1s pound out 10-second passes on the dragstrip and lay down scorching runs on the chassis dyno without a hint of clutch problems. That's quite an accomplishment considering the LS9's TVS-style supercharger, which is known for its big, aggressive torque curve. (Rumor has it that GM engineers have actually tested this clutch up to a staggering 800 lb-ft.) We should note that the ZR1 isn't the only OEM vehicle to offer a twin-disc clutch setup: Its archenemy, the Viper, has one behind its V-10 powerplant, and the V-8 Challenger does as well.
Thanks to the aftermarket's ingenuity, ZR1 technology is no longer limited to the top-of-the-line Vette. We recently road-tripped to Redline Motorsports in Schenectady, New York, to follow along as the shop converted a base C6 Vette from a single-disc clutch combo to a ZR1 dual-disc setup. The conversion is relatively easy, thanks to a combination of parts from GM and Lingenfelter.
Redline's list of components for this swap show a ZR1 slave cylinder (PN 24237569, $237.34 from local dealer), a ZR1 clutch (PN 24237568, $624.54), and a Lingenfelter Performance Engineering flywheel (PN L360010105, $824.95 from Redline Motorsports). The guys at Redline did suggest that a pilot bearing might be required for Corvettes with high mileage or hard use.
Our test subject was an '09 Corvette whose LS3 had been warmed over with a custom Redline Motorsports camshaft, CNC-ported factory heads, American Racing Headers long-tubes and exhaust, a cold-air kit, and a custom Redline ECM calibration. In this trim, the Vette spun the shop's chassis dyno to an impressive 506 rwhp and 455 rwtq. The stock clutch had been holding up fine to the torque output, but with a new Edelbrock E-Force TVS supercharger on the way, the car's owner and the Redline crew felt an upgrade was in order. Shop owner Howard Tanner estimated that rear-wheel power and torque would swell past the 600 mark with a modest 5-7 psi of boost. "This C6 definitely needs an upgraded clutch with the forthcoming Edelbrock blower," he said.

Hotaling then unbolts the...

Hotaling then unbolts the torque tube, the transmission-cooler lines, and other hardware. He lowers the drivetrain down in one piece and then unbolts the bellhousing.

Bruce Hotaling of Redline...

Bruce Hotaling of Redline removes the rear axles and begins unbolting the differential housing.

Here's a comparison of the...

Here's a comparison of the two clutch discs. On the left is the factory C6 disc, which checks in at slightly larger than 11 inches. On the right is one of the ZR1 clutch discs, with a diameter of 10.2 inches. But because there are two discs in the ZR1 unit, the overall surface area is far greater-meaning more grip.

Over the years, the surface...

Over the years, the surface material of clutch discs has evolved. Not only does the latest material offer better grip, it also lasts longer.

The ZR1 clutch is stacked,...

The ZR1 clutch is stacked, and a separator plate (or floater cage and plate) goes between the two discs.

A ZR1 pressure plate is also...

A ZR1 pressure plate is also included in the GM clutch kit.
The installation was quick and fairly straightforward, and the result was a factory-like clutch-pedal feel, but with extra grip. "We add this clutch setup to C6 Vettes, as well as to the DeNooyer Chevrolet HTR-edition Camaros," said Tanner. "It's a great clutch with a factory feel to it. Many of our Vette customers are concerned about the clutch, but also want the power. They don't want something that has too heavy of a pedal feel for everyday driving."
Thanks to the extreme environment of racing, the street enthusiast can now build the wildest engine combinations and have a clutch capable of holding the torque and horsepower-without getting calf implants just to step on the pedal.

On the left is the stock flywheel,...

On the left is the stock flywheel, and on the right is the new Lingenfelter steel unit. The Lingenfelter piece is 5 pounds lighter than stock.

Hotaling adds Loctite red...

Hotaling adds Loctite red to the flywheel bolts and torques it down to 74 ft-lb, using a stepped process and alternating bolts as if he were tightening wheel studs.

The ZR1 clutch stack is taller...

The ZR1 clutch stack is taller than its single-disc counterpart, so a ZR1-specific hydraulic slave is required. It's on the left, while the stock C6 slave is on the right.

Lining up the clutch is crucial...

Lining up the clutch is crucial with both the twin-disc and single-disc setups. Redline uses an input shaft for this purpose. The pressure plate is then bolted to the flywheel using 37 ft-lb.

One of Redline's tricks to...

One of Redline's tricks to getting the bellhousing back on is to loosen the front cradle and ball joints, and relieve the bottom shock nuts. The parts can then hang freely without being removed completely.

Loosening those parts allows...

Loosening those parts allows enough room to squeeze the bellhousing back on. It's torqued to 35 ft-lb.

The torque tube is bolted...

The torque tube is bolted on, and dowel pins are used to line it up with the bellhousing.

The rear differential, the...

The rear differential, the transmission, the torque tube, and the trans-cooler lines are bolted back into the Vette. The rear axles are slid into the differential, and the rear cradle is reinstalled.

With the drivetrain back in...

With the drivetrain back in place, the ARH headers and exhaust system are reinstalled.