Differential: RPM Transmissions upgrades stock differentials for cars mostly used on the street, using compressed carbon clutch packs in place of the stock bronze clutch packs, among other modifications. There are also a few aftermarket differentials that provide greater capacity than the stock diff, but when it comes to the quickest of the quick, the Quaife torque-biasing differential is the only option. Unlike other differentials, it does not incorporate clutch packs-it's strictly all gears inside, for maximum strength. Sets of floating helical gear pinions mesh to provide "normal" performance, but in the presence of wheel spin, torque bias is generated by the axial and radial thrusts of the pinions in their pockets. The friction forces that result and enables the diff to transmit a greater proportion of the torque to the appropriate wheel. According to Quaife, it's a progressive process and doesn't entirely lock the diff. It's not a cheap solution, but a bulletproof one.
Differential housing: C5 and C6 Corvettes have used a variety of differential housings, of different sizes and strengths. However, there are only two real choices for performance levels we're talking about in this story: C6 Z06 and ZR1, with the ZR1 offering the greatest strength. These housings are not only stronger than other Corvette models, they're large enough to swallow a greater diameter ring and pinion. The C5 housings are the smallest and weakest, and upgrading your C5 with the aforementioned Z06 or ZR1 housing means you'll also need to swap in the rear chassis cradle from a C6.
Output shafts, CV shafts, etc.: We're getting near the literal and figurative end of the drivetrain here, with the parts that convey torque most directly to the wheels. The output shafts from the differential need to be as strong as possible. Replacing the stock shafts goes without saying, but aftermarket shafts are not created equally. RPM Transmissions has had the best luck with shafts created in conjunction with The Drive Shaft Shop. They're stronger than 300M steel, with rolled splines that maximize their strength. After that, stronger CV shafts are needed and even stronger wheel studs. A pair of output shafts will run about $550, but the CV shafts are considerably more expensive. The Drive Shaft Shop's shafts run about $2,295 a pair. Again, not cheap, but that's the price of going fast.
There you have it-the basics of making an IRS-equipped Corvette deliver consistent and safe 8-second performance. And as Massengale mentioned at the beginning of our story, suspension factors must be matched with the stronger drivetrain parts, because they will all be wasted on the starting line if wheel-hop cannot be overcome. "It's amazing the numbers these Corvettes are running with an IRS," said Massengale. "You might be surprised by how little drivetrain breakage there is, but we've worked really hard over the years to find what works. If you can put the power to the ground without shaking the wheels off, the parts are available to make an IRS car run just about as quick as you want."
We'll be looking for 7s this season.