Manual swap Differential

[Itsnotme1988]

I have most of the parts I need for my 5-speed swap into my 525iT. What differentials will work? If it will work, I am considering the 3.46 from the manual 535i. Or would it be better to just get a 3.23 from a 525i?

Also, how bad will the revs be on the stock 4.10, if it will bolt right up?

I'm hoping this will be my summer break project

[ILoveMPower]

3.46 might be a little low for the M50, might be perfect

4.10 will be at like 4500 on the highway

[Itsnotme1988]

4.10 will be at like 4500 on the highway


Holy hell! That's outta the question then:p

[John B.]

5th gear in the 525 5 speed is 1.00. In the 535i tranny it's .81 making the 525i 19% lower. With the same (3.46) rear diff the 525i is going to rev much high. If you do much highway cruising you might want to stick with a stock 525i manual diff.

[Anton CH.]

5th gear in the 525 5 speed is 1.00. In the 535i tranny it's .81 making the 525i 19% lower. With the same (3.45) rear diff the 525i is going to rev much high. If you do much highway cruising you might want to stick with a stock 525i manual diff.
But that most likely means no LSD.

[John B.]

But that most likely means no LSD.

Why? None of the 5 speed 525i models came with LSD?

[Itsnotme1988]

Okay, I've been crunching numbers on an engine calculator and found this out using the 3.23s and 3.46s on a 1:1 transmission output on a 25.5in OD tire (roughly a stock 205/65-15)

Rearend 3.23 3.46 4.10

60mph 2550 2750 3250rpm
70mph 2990 3200 3800rpm
80mph 3400 3650 4325rpm
100mph 4275 4550 5425rpm

So I don't think the 3.46 will be too extreme, if it will be a direct bolt in swap. Will the acceleration difference be highly noticable over the 3.23?