The smallest part can often be the source of biggest gain regarding Pontiac power. Evidence can be found in the ring-and-pinion gear swap. Pound for pound, dollar for dollar, this change can provide you with more usable performance than many more expensive and complex modifications.
When considering a rear-gear swap, start with an overall view of the intended use for your Pontiac. For instance, your daily driver is not going to make you happy if you stuff in a set of 4.10:1 gears and hit the freeway. You're also going to be disheartened if all you do is drag race, and your car leaves the line like it's mired in molasses because of 2.56:1 cogs that were intended for highway and economy use.
The parts for our swap included...
The parts for our swap included the GM 10/342 ring-and-pinion gear set from Precision Gear and the Ratech RAT-301K installation kit. After examining the Ratech kit, we opted to buy a Fel-Pro RDS-55028-1 differential cover gasket rather than use the paper-style one supplied.
Selecting our gear set was done via a mathematical formula and tempered with a good dose of common sense. The formula for the rear-gear ratio is (rpm times tire diameter)/(mph times 336) equals the rear-gear ratio. For example, (3,000 rpm times 26 inches)/(65 mph times 336) equals 3.57 for the rear-gear ratio. This calculation allowed us to select an rpm range we thought we could live with on the highway and still run the tallest gear that was practical for a street/strip setup.
The subject of our gear change is a '74 462ci Trans Am. It was originally equipped with air conditioning, which mandated a 3.08 gear set from the factory. The closest applicable gear offering for the 8.5-inch, 10-bolt rear is the 3.42 ratio.
After some discussion with Bryan Blocker of Blocker's Performance and Restoration in Vilonia, Arkansas, we decided to replace the carrier bearings and pinion bearings while doing the swap. His reasoning was that the OEM bearings had more than 30 years of wear. Even if they passed a visual inspection, it would be foolish to disassemble the rearend without replacing the bearings. The axle bearings had been replaced a few months before.