Getting an xr diff for my ef futura this weekend and I.had a few questions. I'm getting it with the xr control arms too, as I heard that this would help with the new diff and the car being lowered. I don't know much about this yet, but there are two control arms, upper and lower? What do these do essentially and what are the advantages of the xr ones? Do I want both lower and upper? do I need to get a tune or alter the speedo with the new 3.45 diff gears? What if I got something like 3.7 gears, then would it need playing with?
Any help/advice to these questions would be much appreciated. Dont mean to sound newby, just dont want to learn this s**t after diff goes in and bad stuff happens.