The cabs are generally the same as the auto's, 3.46. However, the 330 cab is 3.07. BMW makes up for the extra weight of the cabs and the slush box in the autos by shortening the gearing. This keeps the 0-60 and 1/4 mile times somewhat consistent.
All non-M E46's use the exact same differential, just different internal gear ratios. The ONLY exception to this is the 330's input AND output flanges. However, if you are doing a differential swap, you can also swap out the flanges. The flanges on the differentials are completely interchangable. Therefore, you shouldn't have to buy any new parts. The input flange is removed by simply unscrewing a 30mm nut and popping off the flange. The output flanges just pop out...no nuts.
The M3 uses a completely different diff and it won’t bolt up to the subframe of a regular E46 without serious modification.
Garrett, if you have a 330Ci manual, you could go to a 3.15, 3.38, or a 3.46. If you have an automatic, you would need to go to a 3.46. I went from a 2.93 to a 3.46 and I noticed a huge gain in acceleration. However, I also lost top end speed. After the swap, I am at 4000 rpm's at 80mph in 5th gear. It seems like a high rev to cruise at. That was on my 17's. Now, my 19's have made it a little better and I am extremely happy with my 3.46. Keep in mind that bigger wheels will manipulate your gearing as well.
It seems you are knowledge on the issue of changing the flanges during a diff swap. I have a manual 330 with the 2.93 diff. If I go to the 3.46 from the 325 auto (I believe), I will need the input and output flanges from the 325 to make it fit? If I go with the 3.38 from the 330 auto, would I need the input and output flanges from the auto since they are the same make (i.e. 330)?
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