Hows things guys I have a question in regards to diffs.
I have a s4 stage two extend port micro tech ecu and lots of other goodies its putting out 323 houses at rear wheels, It currently has a auto lsd diff 4.10 ratio.
Would it be better to run a manual lsd 3,909 ratio? The car is mainly used as a weekender and for the odd drag day etc.

 

Do you want taller gearing? Using a 3.9 rear end will reduce acceleration & increase top speed. Since 5th gear on a j-spec transmission will top out around 150 mph using a 4.1 rear end, there's not much point to aiming higher. The only real benefit would be slightly lower cruising RPMs.

 

Not to worried about top speed, would like better times when I take it out to drags but have trouble withtraction as it is.