At a glance, there's nothing that indicates Al Brodbeck's C5 Z06 is a capable of low-9-second e.t.'s. Apart from the racing wheels and tires, it looks stock and the Vortech YSI-trim blower generates little aural clue to the capability under the hood. But when this Corvette launches, time seems to stand still and all too soon the board lights up at the far end of the strip with stunning numbers. The best performance to date is a 9.04 at 159.96 mph-with what Brodbeck describes as a "lousy" short time in the 1.50-second range. More remarkable is this car squats, launches, and freight-trains down the track with little drama, all while still channeling its power through the C5's independent rear suspension (IRS). As impressive as Brodbeck's performance is, it's not an anomaly. These days, 9- and 8-second C5 and C6 Corvettes are regular sights at tracks around the country and, surprisingly, many aren't leaving chunks of half-shafts at the starting line. That's not to say these cars are performing their warp-speed e.t.'s through stock axles, of course, but the fact they're doing it through an IRS (at all) flies in the face of conventional drag racing wisdom.
"Those racers are really pushing the envelope, but with the right drivetrain parts and suspension, you can get an IRS-equipped Corvette into the 7s," says Rodney Massengale, founder and president of RPM Transmissions-and he should know. His Anderson, Indiana, shop has been on the front line of enabling C5 and C6 Corvettes to go quicker without shedding parts. "It's not just about a stronger differential and axles-although they definitely play a crucial role," says Massengale. "It's the whole drivetrain that must be strengthened to support this level of performance. It's like that saying about a chain only being as strong as its weakest link."
Of course, strength is a relative term, and what's strong enough for a 10- or 11-second street/strip car isn't as strong as the needs for low 9s and 8-second e.t.'s. As Massengale pointed out to us, there are options for every level of performance, from comparatively simple upgrades of the stock components to the complete-and, yes, expensive-replacement of essentially the entire drivetrain. He also told us the biggest killer of transmissions and rearends wasn't too high horsepower or torque channeled through weak parts, it was abuse and wheel-hop. "We've seen cars with only about 400 rear-wheel horsepower break the differential housing because of wheel-hop and we have customers who send twice that power through a basically stock manual transmission because they know how to launch correctly and shift precisely," says Massengale. "Once you've got the suspension dialed in and can launch without wheel-hop, you're half way there. But if you can't beat it or you keep missing shifts, the strongest axles in the world won't save you."
The really quick Corvettes we've encountered, however, aren't running beefed up stock parts; and because we were interested in how they were making it happen, Massengale walked us through the setup his shop put together for Ohio customer Mark Carlyle. At the time we finished this story, his Atomic Orange, single-turbo '07 Z06 is the quickest IRS C6 Z06 on record, running 8.15 at 173 mph during the 2010 season. "Starting at the engine, Mark's car runs a new flexplate and bellhousing, along with a new driveshaft and driveshaft couplers," says Massengale. "The transmission is a Turbo 400 and the differential is a Quaife set in a Z06 housing. And, of course, the output shafts are stronger and even the CV shafts and wheel studs are stronger. It's a complete system from end to end, backed up with the right suspension."
Starting at the front of the drivetrain, here's an outline of how and why the components are strengthened: