LT1 Formula Upgrade - Putting Your Rear In Gear Part II - Tech

In our last installment, you may remember that the 100,000-mile stock 4L60E in our LT1 Formula project car was swapped for a TCI Super Street Fighter. With the help of the TCI Saturday Night Special torque converter, MaxShift tranny fluid, and trans cooler, the Formula was pretty well set for an all-out assault on the pavement; however, just to be safe, the torque arm and rear-lower control arms would also need to be upgraded with the help of BMR Fabrication. Additional power and an increase in weight transfer from the BMR suspension components meant the stock 7.625-inch 10-bolt and 2.73 gear were sure to betray the Formula at any moment. Thankfully, TT Performance in Passaic Park, New Jersey, went the extra mile in beefing up the stock 10-bolt rear with Moser 28-spline axles, an Eaton posi, TA Performance girdle and studs, and Motive 3.42 gear to bring the LT1 into its powerband.

It doesn't take long for the stock posi to go, as the familiar one-wheel-peel has become popular at test and tune night at the dragstrip. This is easily amended with an Eaton posi, which happens to be one of the strongest, most reliable, and streetable differentials on the market. Its open-style limited slip allows chatter-free power transfer to both axles via super strong carbon-disc clutch packs. The 10-bolt's most infamous downfall, however, is its small ring gear, which is only fully amendable by forking over more than $2,000 on a 12-bolt or 9-inch. Those looking to save $1,000 or so by utilizing the 10-bolt would be wise to replace the worn stock ring gear, which also provides the perfect opportunity to install a more performance-friendly ratio than the 2.73, 3.23, or 3.42 gear Fourth Gens come with. This Formula is unfortunately adorned with the worst of the three-the 2.73 ratio-which put the LT1 out of its powerband for most of the quarter-mile, barely shifting into Third before reaching the stripe. With the help of Motive Gear, we could increase the ratio to 3.42. Though 3.73s or 4.10s would better suit the LT1, the 3.42s were much more ideal for maintaining gas mileage with the everyday highway time the Formula sees.

Though the stock GM 28-spline axles have never been known as particularly weak, we ordered up a set of Moser 28-spline forged steel C-clip axles to cover all the bases. I thought perhaps one day the Formula might exceed the NHRA's 10.99 ET limit on stock axles. To do so, we'd need a prayer and a TA Performance Rear End Girdle. In addition to increasing the fluid capacity of the rear by about 1/2 pint, the 356 aircraft-grade T6 aluminum cover also provides support to the main bearing caps. Last but certainly not least, a set of Nitto NT555R DOT-approved drag radials provide the grip. At 245/50R16, the Nittos are 25.67-inch tall, and won't eat up too much of the modest 3.42 ring gear, while still keeping a decent contact patch with 9.80 inches in width. The soft race compound has proven itself quite sticky in past builds with a good smoky burnout, and it also serves well during normal street driving because of its tread pattern and depth (though not appropriate for those in wet or cold climates). With these tires bolted up to a used set of SLP 16-inch ZR1-style rims, we were hoping to break into the low 13s-or possibly even high 12s with decent air at Englishtown.

	In our last installment, the TCI Super Street Fighter 4L60E install was finished up by securing it with a TCI polyurethane trans mount and hooking up the TCI trans cooler.
And now it's time to enlist the help of BMR Fabrication, which hooked us up with a set of adjustable chrome-moly lower control arms (PN MCA002), weld-in control arm relocation brackets (PN CAB001), an adjustable torque arm (PN TA001), and a driveshaft safety loop (PN DSL001) to plan ahead for our future 11-second NHRA legal timeslips. Note that the torque arm and control arms come with polyurethane bushings perfect for street-driven hot rods like the Formula.