Best diff for economy?

[German-Whips]

I've recently bought a 325i cab which started it's life off as a 318i.

I'm assuming the diff is still the original 318i diff, as I'm not aware of it having been changed.

What is the best differential to go for if I'm looking for fuel economy? I'm not too worried about performance at this stage, as it's a daily driver.

How would the 318i diff currently in the car perform in terms of economy and general driveability?

Any recommendations?

Thanks

[Speedtouch]

http://www.e30zone.net/e30zonewiki/inde ... fferential

The highest gear (3.46:1) fitted to a 325i, is my guess.

[e30rapidic]

first thing you need to do is check out and see what ratio you actually have in there. 318's came with 4.45, 4.27, 4.10, 3.91 and 3.64 ratios.

[daimlerman]

Diff size is important as well!

With a 325i,you really need a medium case diff,318i came with a small case version.
How to tell the difference?

Slide under the rear end and count the bolts on the rear cover,small has six,medium has eight bolts.

Best ratio?
3:64,gives 73mph at 3000rpm,with a manual 'box.

[jon-m42]

A good post this:

Not to take over but staying on topic id like to ask ...:

My question here is being it a standard m42 would the 3.91lsd alone improve the economy over a 4.10lsd?

I presume I at present have a regular open 4.10 diff not lsd.

Thanks
Jon

[Grrrmachine]

LSD or not won't make a blind bit of difference to the economy. The difference between 3.91 and 4.10 might make some negligible difference on long drives, but since it blunts acceleration you may find your fuel use goes up, since you'll need to rev the car a bit more at each traffic light.

As for the 325i, I was told to avoid the old diesel diffs (3.45, 3.25) as they'd be too blunt even for the mighty M20B25.

[pacerpete]

3.73 is a good allrounder in a heavy convertible . 3.64 will theoretically give you slightly better economy on longer journeys at higher speeds but few use a convertible for that.


RE M42 freak above

Unless your original diff is goosed, there is no point swapping in a 3.91, the theoretical fuel savings will take several years to pay for the diff swap !

[hongkongfuey]

I have a 373 in my touring its good all round like pete said

[jon-m42]

RE M42 freak above

Unless your original diff is goosed, there is no point swapping in a 3.91, the theoretical fuel savings will take several years to pay for the diff swap !

I am sure you have much more knowledge then me around these motors and I am also sure you have been around these cars way more then I have had hot dinners however I can assure you I am not as much of a freak as you pal.

Cheers

[pacerpete]

RE M42 freak above

Unless your original diff is goosed, there is no point swapping in a 3.91, the theoretical fuel savings will take several years to pay for the diff swap !

I am sure you have much more knowledge then me around these motors and I am also sure you have been around these cars way more then I have had hot dinners however I can assure you I am not as much of a freak as you pal.

Cheers

YOU have an IS , the end