Been looking around at duffs and ratios that would be a bit taller than the 3.62 sierra unit I currently have.
I'm running a zzr1100 and it kinda revs out at around 95mph. Great fun getting there but it could just do with being a little taller to bring the revs down a bit at sensible cruising speed. (It's a bit "buzzy"

So ideally a 3.14 sierra diesel unit, but big money. What other options? Freelander?.......... I have found this: bmw 1 3 series diff 2:79 ratio
Anyone had any experience with BMW diffs?

Suppose a lot depends are you capable of welding in new mounts etc for a different diff?

If so you can use what ever diff will physically fit in the space.

If you are looking at paying someone to take on the job the price would soon pass the premium price of a sierra diesel diff which you could just bolt in.

A change of Sierra diff will only need the diff and some time.

A change to a BMW diff (for example) will not only require the diff but some modifications to the chassis and some changes to the drive shafts and prop shaft. The drive shafts may need to be hybrids if you want to keep your existing hubs/brakes etc so the cost will mount rapidly. As will the time needed.

I know a Sierra diff is not light by any means but is a BMW diff any lighter?

http://www.locostbuilders.co.uk/viewthread.php?tid=192986

I suspect still not enough if its topping out at 95 and 314 is your best bet?

I'd think a 2.79:1 BMW diff wouldbe a bit long.

Freelander is 3.21:1 ratio and lighter than Sierra. You'd need hybrid shafts and alterations to your chassis mounts though.

Simplest would be stick with Sierra. What about the 3.38 diff? That's a popular choice. Have a look at the SPREADSHEET in this thread. Plug your details in and see what speeds it gives you.

[Edited on 5/8/14 by adithorp]

dont know ratios but mx5 diffs are plentyfull at the mo? just a thought

Are you sure your speedo is accurate? According to the spread sheet you should top out at 114mph in 6th (zzr1100, 3.62 diff and 185/60/13 tyres)

195/50 15's
Welding isn't a real problem. Have done a little bit of that recently for another builder who had a slight argument with a lamp post.
Speedo accuracy.... Hmmmm? Maybe. But it's still way buzzy at 70.

I'm basically looking for a cheap solution until I can afford to start the new project. Just so I've still got a toy to play with while I'm building the beast.
It helps to keep the interest going.

Next project is gonna be 4x4 skyline power!