'66 Dart Wagon - Swapping out rear end for a 8 1/4 - gear ratios????

Hi All,

I am new to the Forum and a newbie to working on rear ends. I want to convert to front disc and go up to LBP wheels. So I am going to swap out the rear end and looking at 8 1/4.

I have found one for $500 (I am in Southern CA) that was taken out of a '74 Duster. It has a 4.10 gear. Looking at the specs of my Dart, the manual says it has 2.93 gear in the 7 1/4.

My dart is a 225 slant six. How will this 4.10 gear ratio affect overall performance of the car? Mileage, etc.

Any suggestions for a newbie.

Steck