(Courtesy of TurboVic) Gear choice depends on several things, it’s a trade-off. The more gear you get, the faster you can accelerate, to a point. The trade off is that your gas mileage will suffer with each step up on the gear chain.
Most civilian Crown Vics come with 2.73 gears, 3.27 in the performance and handling package (99-00 Vics with P&H get 3.55’s). Police interceptors get 3.27’s from the factory, which was upped to 3.55’s for 99-00.
All civilian Crown Victoria’s come with open differentials, which means you will only leave one mark when you try a burnout. 3.55’s should be the minimum you should consider to up the performance of the Vic. 3.73’s are a much better choice and are still very good with gas mileage. 4.10’s would be about as far as I would go on a modded Vic due to the fact you run out of revs at around 4250rpm.
Regardless of which gears you choose, consider it a good time to replace your differential at the same time, the labor is not extra when doing a diff and gears at the same time. Most shops will charge between $250-300 for installation, add an extra $100 if your bearings are shot.
You will need a 23 tooth speedometer gear to switch to any of these gears. With 3.55’s, your speedo will read about 3mph slow at 65mph. With 4.10’s, it will read about 3mph fast. 3.73’s will read about perfect. On the newer cars, you’ll need an electronic speedometer compensator, which is available from Abbott.