10 bolt axles have 3.23 gears, while our 9 bolt axles have 3.27 gears. The GTA's and IROC-Z's could have a 10 or 9 bolt axle depending on the engine\trans combination. A friend of mine used to own an '89 GTA 5.0L TPI with a 5 speed, dual cats, and a 3.45 geared 9 bolt. It was a quick car for a GM 5.0L...