If you have been around third- and fourth-generation F-bodies for any length of time, you probably already understand that the stock 7.625-inch 10-bolt rearend isn't exactly the strongest unit on the planet. In fact, one could argue that the factory 10-bolt is possibly the least capable rearend GM could have used in these high-performance muscle cars. Besides being physically small, the factory rears seem to have an issue keeping teeth on even the stock ring and pinion, a problem that gets worse with every additional ft-lb of torque you throw at it. Replacing the ring and pinion can even make the problem worse, as a steeper gear (numerically higher) means the teeth have to be thinner, further weakening the rearend and making it even easier to break. To add insult to injury, most factory and aftermarket 10-bolts, even in working condition, can exhibit a nasty gear whine, the result of both subpar installations and distortion.
So, with all of that in mind, why would anyone choose to risk building a 10-bolt, especially in a car like the STi Killer that will be abused on the dragstrip, road course, and street? Well, first of all, the 10-bolt is very light and less weight means faster turn-in, better handling, and quicker acceleration. The 10-bolt is also efficient, which means it will help us put more horsepower to the ground, instead of soaking it up as drivetrain loss. Options for the 10-bolt have come a long way since the early days and many great companies now offer quality parts for these units at an affordable price. While a $2,000-plus 12-bolt rear was tempting, we just couldn't squeeze it into our budget, a phenomena that is becoming increasingly more prevalent in these tough ecomonic times. And last but not least, we realistically don't plan on putting an earth-shattering amount of horsepower or torque through our rearend and as such, we felt like a quality 10-bolt build would easily be able to handle the demands of our hopped-up GMPP LS6 engine, while offering many benefits over a big, overbuilt drag racing-oriented aftermarket unit.
So, where to start? For a build like this, with many different pieces and manufacturers, we turned to Summit Racing, a company you are no doubt familiar with. Sure, we could have ordered each piece separately, but the hassle and cost of shipping wouldn't have been worth it. With Summit, one phone call got us everything we needed at a great price and it showed up a couple of days later, all laid out and ready to go. Our biggest ticket item was a new Eaton Carbon Limited Slip differential (PN ETN-19599-010) that we hope will be able to quickly and accurately distribute power to the correct rear wheel, giving us maximum locking power when we need it and quick differential action when we get into the tight corners of an autocross course. Another bonus of the Eaton Carbon unit is that it is highly rebuildable, which means after a couple seasons of racing we can tear down the unit and replace what is worn without having to purchase an entirely new piece. Along with the 28-spline Carbon limited slip we also ordered a 4.10:1 ring and pinion assembly from Richmond Gear (PN RMG-6903221). Coming from a sluggish 3.23 or 3.42 factory gear to the 4.10 will help greatly improve our acceleration, both in a straight line and out of a corner, which is where we will need it the most. Along with the improved acceleration, the 4.10 ratio should also help keep us higher in our powerband around the road and autocross course, which means less downshifting and smoother power delivery out of the corners and onto the straights. Of course, we would never install a ring and pinion without a matching install kit and for that we chose to go with Richmond Gear's Mega ring and pinion installation kit (PN RMG-831016M). The Mega kit comes with everything you could ever need for a fresh rebuild, including all of the bearings, races, seals, gaskets, nuts, and marking compound for a complete installation. If you are going to tackle this install, it just makes financial sense to change all of the bearings and seals at once, since tearing the rear down later will end up costing you even more money. With our centersection taken care of, we splurged a little and ordered a new set of Alloy USA axles (PN ALY-17136) to replace our stock units. These Alloy USA pieces also need a new set of wheel studs, which we chose to upgrade with a set of ARP extended studs (PN ARP-100-7713).
Last but certainly not least, we had to find a qualified rearend expert to piece everything together. As it turns out, building a quality, long-lasting rearend is almost a black art and it requires a special someone with extreme patience, knowledge, and skill. We lucked out and found Bruce Ponti, right around the corner in Seffner, Florida, who works with our friend Greg Lovell at AntiVenom. Bruce has been building rearends since before I was born and definitely helped us learn a couple of quality tricks while putting our 10-bolt rear together. Follow along with Bruce and Greg as they work through a complete rebuild of our factory 10-bolt. The next time you see the STi Killer, it will be loaded up with all of its drivetrain goodies and ready to do battle.