Z4 3.0i change differential to shorter

[feket663]

Hi Community! I have a 2005 Z4 3.0i with M54 engine. I don't care about top speed, but I'd like faster acceleration. I found a relatively cheap differential in good condition from 2.5i. Unfortunately, European 2.5i models are equipped with a 3.23 gear ratio differential. Will this make a noticeable difference or should I look for a diff with 3.46 ratio?
The original ratio is 3.07.

Thanks for help!

[grannyknot]

You may notice the difference between 3.07 to 3.23 but it won't be much, a jump to 3.46 will be noticeable and will give you a nice kick on take off.
If you can locate a 3.64 which are common, at least here in North America, then that would be better.
You may be tempted to go 3.91 or 4.10 but just remember that your gas mileage will suffer when you're in 5th or 6th on the highway as the revs will be higher.

You pay for at the top end what you reap at the low end and vice versa.

[Steeler]

I have run the gambit, looking for my perfect ratio.
From 3.23 all the way to 4.44. yea that was just an experiment.

I decided the 3.91 was the right fit for me.

You are not limited to E85/86 diffs.
Most of the shorter ratios I sourced from E83 X3.
Also some E46 will fit.

Do your research.

https://web.archive.org/web/20200622...GearRatios.htm