[jgsrna]

i just got a set of gears of 3.55 for my 66 mustang 289! was that a good choice or should i have gotten 3.90! how much would it cost to install? would i feel a differnce now with the 3.55?

[jerryt]

3.89 gear ratio is the the best for that year car, you feel the diffrence, i used the same rear in my 66 back in 69, with a 289 eng that turned 8500 rpm.

[Vortex]

better gears you'll def feel improvement. 3.55's will give you a step towards a stronger while still maintaining fuel mileage on highways. I don't think you'll be sad if you put them in.
I didn't have time to install my 3.55's so I took it to a shop and they charged me under $100 but I also brought them the gears, and a full differential rebuild kit (spacers, bearings, seals, etc) that I got from Summit.