Hey guys just bought a 95 z28 a4...at 60 mph I'm at around 1800 rpms...is this stock gearing? How much would 3.73 increase and therefore theoretically how much faster assuming power is laid to the pavement?

 

Stock 3:23 ??

 

Yes, that's the RPM you would see at 60MPH, with an A4 in O/D, stock tire diameter and 3.23 gears. You can also look at the service parts label (end of drivers door or in glovebox) for RPO code "GU5" which indicates 3.23's. The base gears on the V8 A4's were 2.73 (GU2). If the car was ordered with the "performance rear axle" option, the gears were 3.23.

If you swap in 3.73 gears, the RPM at 60MPH will inrease to 2,080 RPM. At any given speed, the RPM will increase by 15.5%. You will also feel like you added 15.5% more torque at the rear wheels on launch, but of course your trans will be shifting gears at 15.5% lower MPH.

PCM needs to be reprogrammed for the gear change.