[CobraMarty]

Here are the available ratios- 3 Series - E9x

328i MT- 3.23, also 325i MT
328i Auto- 3.73, also 325i Auto
328xi MT- 3.38, also 325xi MT
328xi Auto- 3.91, also 325xi Auto

330 MT- 3.15 (i or xi)
330 Auto- 3.64 (i or xi)

335 MT- 3.08 (i or xi)
335 Auto- 3.46 (i or xi)
M3- 3.85
335d- 2.81

If you have a 328 2WD i version, you have all the different rear diff ratio options.
If you have the 328 AWD xi version, your diff ratio choices are limited because you need a matching front diff ratio. Available ratios are 3.08, 3.38, 3.46, 3.91.

I have a 328xi MT which has the 3.38 diff ratios.
Yesterday I scored front and rear diffs from a 328xi Auto with 3.91 diff ratios for $300 shipped complete with drive shaft and axle flanges.

I am going to swap out the front and rear diffs with the 3.91 ratio diffs.

No LSD at this time. The 328 is HP limited (compared to 335) and no real rear traction problem especially with the xi front diff/traction.
If traction does become an issue, I will install a Quaffe or Wavetrac diff in the rear. $$ VAC gets $2200-2500 to rebuild the rear diff and add the LSD. Not going to spend that money now.

[stewey]

Thanks for the list. You might want to add entries for the 330 and 325.

[mike-y]

the 325i shares the same ratios as the 328i.

Not sure about the 330i vs 335i tho.

[CobraMarty]

I have a 328xi, but I added the 325 and 330 for you guys.
But for what fits what, IDK.

I expect my '07 328xi MT 3.38:1 will accept the '08 328xi Auto 3.91:1 diffs, just bolt in.

[Jashley73]

Good to know. Thanks for posting!

[CobraMarty]

Originally Posted by vha27

Correct, for a RWD only. XI version is a little different.
http://www.bokchoys.com/differential/GearRatios.htm

Here is where I found the info. Thanks and credit to vha27.

It was this info that gave me the idea to swap the 328xi auto 3.91 into my 328xi MT 3.38.

[CobraMarty]

Got the 2 diffs yesterday UPS. Both in one box 105 pounds total. The front is surprisingly small and light, rear obviously cast and bigger and heavier.
I will look closer at them later.

[328XIdiot]

Any update? Rear diff swap seems easy, but the front?

[CobraMarty]

Haven't started yet. Need to install the lift in the garage first.

[328XIdiot]

Well...a lift should help a lil

[bmwstandfor]

Originally Posted by CobraMarty

Here are the available ratios- 3 Series - E9x

328i MT- 3.23, also 325i MT
328i Auto- 3.73, also 325i Auto
328xi MT- 3.38, also 325xi MT
328xi Auto- 3.91, also 325xi Auto

330 MT- 3.15 (i or xi)
330 Auto- 3.64 (i or xi)

335 MT- 3.08 (i or xi)
335 Auto- 3.46 (i or xi)
M3- 3.85
335d- 2.81

If you have a 328 2WD i version, you have all the different rear diff ratio options.
If you have the 328 AWD xi version, your diff ratio choices are limited because you need a matching front diff ratio. Available ratios are 3.08, 3.38, 3.46, 3.91.

I have a 328xi MT which has the 3.38 diff ratios.
Yesterday I scored front and rear diffs from a 328xi Auto with 3.91 diff ratios for $300 shipped complete with drive shaft and axle flanges.

I am going to swap out the front and rear diffs with the 3.91 ratio diffs.

No LSD at this time. The 328 is HP limited (compared to 335) and no real rear traction problem especially with the xi front diff/traction.
If traction does become an issue, I will install a Quaffe or Wavetrac diff in the rear. $$ VAC gets $2200-2500 to rebuild the rear diff and add the LSD. Not going to spend that money now.

I bought the 328xi Auto- 3.91, now try to fit on my 328i 2wd 6spd but I found out that triangle piece not same as my differential, mine is the circle one, how can I fit it on? anyone can help?

[GTKrockeTT]

Originally Posted by bmwstandfor

I bought the 328xi Auto- 3.91, now try to fit on my 328i 2wd 6spd but I found out that triangle piece not same as my differential, mine is the circle one, how can I fit it on? anyone can help?

get the input flange swapped out between the two.

[bmwstandfor]

Originally Posted by GTKrockeTT

get the input flange swapped out between the two.

so after I swap the input flange that centre silver steel piece not stick out anymore? Because my diff dont have anything stick out from the centre

[GTKrockeTT]

i don't recall that section protruding from either of the diffs i had.

[E90_slides]

Originally Posted by CobraMarty

Here are the available ratios- 3 Series - E9x

328i MT- 3.23, also 325i MT
328i Auto- 3.73, also 325i Auto
328xi MT- 3.38, also 325xi MT
328xi Auto- 3.91, also 325xi Auto

330 MT- 3.15 (i or xi)
330 Auto- 3.64 (i or xi)

335 MT- 3.08 (i or xi)
335 Auto- 3.46 (i or xi)
M3- 3.85
335d- 2.81

If you have a 328 2WD i version, you have all the different rear diff ratio options.
If you have the 328 AWD xi version, your diff ratio choices are limited because you need a matching front diff ratio. Available ratios are 3.08, 3.38, 3.46, 3.91.

I have a 328xi MT which has the 3.38 diff ratios.
Yesterday I scored front and rear diffs from a 328xi Auto with 3.91 diff ratios for $300 shipped complete with drive shaft and axle flanges.

I am going to swap out the front and rear diffs with the 3.91 ratio diffs.

No LSD at this time. The 328 is HP limited (compared to 335) and no real rear traction problem especially with the xi front diff/traction.
If traction does become an issue, I will install a Quaffe or Wavetrac diff in the rear. $$ VAC gets $2200-2500 to rebuild the rear diff and add the LSD. Not going to spend that money now.

So if I wanted to buy a M3 e92 MT rear diff and slap it on my 328i MT RWD it will bolt right on?

[E90_slides]

Originally Posted by bmwstandfor

I bought the 328xi Auto- 3.91, now try to fit on my 328i 2wd 6spd but I found out that triangle piece not same as my differential, mine is the circle one, how can I fit it on? anyone can help?

that's because you bought an xi (AWD) differential. AND its and automatic and you said you have a 6sp MT? wouldn't fit anyways and you're downsizing in performance. get a MT rear diff RWD and you should be cherry. I've been looking at hundreds of pictures comparing stock 328i MT differentials to other stock MT diffs from other models. looks like I'm going to buy an m3 T LSD for $800

[drw1710]

Is it possible to swap the rear diff as a complete unit from an E9XX into an e46?. I am new to the BMW scene but not to hot-rodding and this seems like the perfect platform for the swap. Also, do any of these cars have an LSD option to look for?

[Phil325i]

OP, just for completeness as a guide for diffs, it's worth pointing out that your figures are for the US market. Diff ratios are different in Europe. For example my E92 325i manual with the N53 direct injection engine (which is quite torquey) has a diff ratio of 3.07.