Flexplate: The stock flexplate is composed of two pieces of stamped steel bolted together. Under high load, it comes under stress at the fastening points. Also, the relatively thin steel plates can crack or tear. Failure of this part is messy and dangerous, so replacing it with a thicker, tougher single-piece flexplate is essential. RPM Transmissions matches the stronger flexplate with a billet steel cone that replaces the stock cast part. Flywheels (for stick cars) aren't nearly as fragile, but also a great upgrade and part of many quality clutch upgrade packages.
Bellhousing: RPM Transmission uses a spun steel bellhousing that is SFI-approved for maximum containment strength. For the quickest cars, the factory aluminum bellhousing is not only inadequate, it's not allowed.
Torque tube/driveshaft assembly: IRS or straight axle, a stronger driveshaft has long been a basic drivetrain upgrade. C5 and C6 Corvettes, however, incorporate a pair of rubber couplers with the driveshaft, inside the torque tube, which simply weren't designed for the rigors of 8-second drag racing. When put under extreme loads, the couplers tend to grow and rub themselves against the wall of the torque tube. Typically this chews up and destroys them. Replacing them with stronger polyurethane couplers is required.
Transmissions: Stick-shift trannies seem to be the hardest things to reconcile with IRS. Only a small handful of people have managed to go fast while rowing their own gears, even though there are plenty of modifications that can be made to enable the T56 and 6060 to handle gobs of power. Instead, specially built 4L60E, 4L80E, and even Turbo 400 transmissions seem to be the ways to go for drag racing. They're built to handle exceptional torque levels, while offering greater consistency. Mark Carlyle's Z06 runs a Turbo 400, while Massengale's personal Z06 runs 9s with a 4L60E. C5 and C6s were offered with 4L60E transmissions, so swapping one into a stick or 6L80E car is relatively easy. Going with a 4L80E or Turbo 400, however, requires surgery. Each is a few inches longer and taller than a 4L60E, so tunnel modifications are required, as well as a shortened torque tube and shorter driveshaft. It's a serious commitment to step up to one of these transmissions, but they're strong and dependable.
"The 4L60E is great for cars running from the 11s into the 9s, as I can personally attest," says Massengale. "If you're aiming for bottom 9s or the 8s, you'll probably want to go with the 4L80E or Turbo 400." And when it comes to deciding between the two, the Turbo 400 is ultimately more adaptable, with a greater range of gear ratios to select. It also offers a faster transbrake and there's no lock-up converter, which the 4L80E has in addition to a fourth (overdrive) gear. In short, it's a true racing transmission. So, what about a Powerglide? There is some debate in the community about whether the two-speed trans is a good option for the C5/C6. Massengale, however, favors the TH400 as he says the 'glide doesn't have the optimal gear ratio for the larger 3.42 ring gear of the Z06 or ZR1 differential. Without the ability to change gear ratios, while running the stronger diff, it would certainly be hard to optimize whatever combination you are running. Case in point, the two fastest IRS cars to date both ran RPM-built Turbo 400s.
Pfadt solid transmission mounts are typically matched with these upgraded transmissions to help minimize drivetrain flex, which translates to a reduced chance of wheel-hop. Of course, a torque converter must be matched with the vehicle's specific combination. Precision Industries or Coan Racing seem to be two very popular brands among the Corvette community.