Hello, i'm mario, i just purchased an 03' Z4 2.5i 5-speed and am currently waiting for it to be shipped over. As i anxiously await delivery I'm already planning out some mods to install once it gets here. The only thing is i'm having a REALLY hard time finding stuff/info for the z4. I come from a honda/lexus/subaru background and those had plenty of parts and websites. Not so much for the Z4. i did try searching when applicable but not much info is out there.

Suspension mods are done already, i have sway bars and springs on the way from H&R. I also have a short antenna on the way too. Those were easy to find.

I know the 2.5i is the same engine in the 325, so engine mods should be the same (i.e pulleys, intake, headers) correct?

I also read about retrofitting an OBC and CC stalk, i have the part number for the CC stalk but not the OBC, any help?

Differential swap: the 5-speeds come with a 3.46 rear gear and it doesn't seem worth it to swap over to a 3.64 as there isnt much change. what about the 3.91 from an x3? Dinan seems to sell a 3.91 lsd diff for the z4 for 1200 so the 3.91 must be somewhat acceptable for daily driving. any thoughts?

thanks for reading!

$1200 limited slip from dinan????? I retails for $2500. Where are you getting that price from???

Here's the full cost data for the 3.91 rear end, all following copy is taken directly from the Dinan website:

Part #: D773-0460

Price: $2499.00
Labor Hours: 5.80
Emission Status: 49 State Emission Legal
Point Value: 2


The shorter 3.91 gearing takes advantage of torque multiplication for a substantial 8% increase in torque delivered to the road. The improved acceleration comes with only a minor increase in engine speeds at cruise and no effective reduction in top speed potential.

The Dinan 3.91 Limited Slip Differential delivers what is perhaps the greatest "bang for the buck" in terms of improved and more immediate acceleration.

yeah i double checked it and was way off (looked at the wrong column).

Man by the time you're done spending, you probably could have bought yourself a nice MZ4 BRAND NEW.

believe me i thought bout it, but the insurance and maint would be pretty high.

at this point i just want a fun lil car to drive.

believe me i thought bout it, but the insurance and maint would be pretty high.

at this point i just want a fun lil car to drive.

Really? Maintenance is the cheaper for the MZ4 because it's free the first 4 years, 50,000 miles. The 2.5 is already out of free maintenance period.

Insurance isn't any higher for my MZ4 Coupe than my Z4 3.0. Unless you're 25 and younger it's not that much more...The only difference is the Z4 would be at least 4 years older and less in value, hence "cheaper" for insurance.

But there are ways around it. :D

I couldn't imagine a higher ratio diff in the 2.5 it is already geared so high. The car needs a 6th gear badly.

this is a good starting point for finding modifications. Understeer carries a lot for the Z4, for example: http://www.bimmerforums.com/vendors.php

Differential swap: the 5-speeds come with a 3.46 rear gear and it doesn't seem worth it to swap over to a 3.64 as there isnt much change. what about the 3.91 from an x3? Dinan seems to sell a 3.91 lsd diff for the z4 for 1200 so the 3.91 must be somewhat acceptable for daily driving. any thoughts?


The 3.91 diff Dinan sells is for the Z4 Ms, not the standard cars. No way would I try a 3.91 on a 5-speed anyway, though you're right that the X3 auto's diff will fit.

What about the 3.0? How would the Dinan 3.91LSD do in my otherwise stock 3.0? Its either that or the 3.46 E46 M3 LSD it seems like.

What about the 3.0? How would the Dinan 3.91LSD do in my otherwise stock 3.0? Its either that or the 3.46 E46 M3 LSD it seems like.

Let me be more specific: NO! Neither of those diffs will fit. :)

The Dinan 3.91 diff is for M cars, the E46 M3 3.62 diff is for M cars, and an M car diff WILL NOT FIT a Z4 2.5/3.0/si wthout replacing the entire rear subframe. I've seen it done once, by someone building a dedicated race car, and he only went to all that trouble and expense because BMW had said there would never be an Z4M. :rolleyes

Your options for an upgrade diff are a non-LSD 3.46, 3.64, and 3.91 from standard non-M BMWs like the 325/330/X3. You can add an aftermarket limited slip from Turner Motorsport or Diffsonline. The whole enchilada will likely run close to $3000.

I couldn't imagine a higher ratio diff in the 2.5 it is already geared so high. The car needs a 6th gear badly.

this is a good starting point for finding modifications. Understeer carries a lot for the Z4, for example:


ah thank you, i was wondering what changes the 3.91 would have on the speed/rpm of the 2.5i now.

thanks! i guess i'll stick to handling and creature comforts first before power, i'll learn the nuances of the car first. thansk all!

I have an aFe Z4 CAI for sale, PM if interested.