I think with a stock tranny, you need a white 23 tooth gear (which you probably already have from your sig). I am not sure you can put another gear (for 3.90's) in a stock tranny w/o chewing it up. Anything above 3.55's take this gear unless you have changed the output shaft gear from what I understand. You can get one on ebay if you need one for around $10 plus shipping. Else you have to change the output shaft gear to get it wher you want it and that is out of my league, but I do remember a thread on it here somewhere recently.