Differential swap

[Cody318]

I bought a mid-84 318i parts car for my early 84 318, and while inspecting the differentials of each i found the parts car to be equipped with an "S 391", meaning a limited slip with axle ratio of 3.91:1 while the early 84 has "364", representing a 3.64 open rear end. Living year-round in Minnesota, would it be a good idea to install the 3.91 lsd? and would the rpm difference be a worry? Thanks.

 

[epj3]

I bought a mid-84 318i parts car for my early 84 318, and while inspecting the differentials of each i found the parts car to be equipped with an "S 391", meaning a limited slip with axle ratio of 3.91:1 while the early 84 has "364", representing a 3.64 open rear end. Living year-round in Minnesota, would it be a good idea to install the 3.91 lsd? and would the rpm difference be a worry? Thanks.

I would find out what the stock ratio is supposed to be - is the car with the 3.91 an automatic (or vice versa?) The 3.91 will lead to a bit worse fuel economy but it should feel peppier.

 

[Cody318]

My daily driver (which would receive the 3.91) is equipped with a 5 speed ZF and 3.64, while the parts car has a 3 speed auto and 3.91. I think the trade-off will be worth slightly lower fuel economy for a limited slip with much fewer miles and better acceleration.

 

[andreyiv]

Sounds like you'll get the best of two worlds; slightly better acceleration, an LSD and slightly lower fuel economy.

 

[echothreezero]

I wouldn't even be thinking about it - the LSD would of been in the car yesterday!

Hop to it - better traction, better control when the car gets tail-happy, and better acceleration. Slightly worse economy on long trips - so what!

 

[equate]

I drove my 325i in MN winters 2 years, it sucks balls. I got stuck every day. I would definatly put a LSD in if you plan on driving in snow.

Where in MN are you?

 

[scrood]

here in Australia, we have NSD (no slip diff)...

we just weld 'em up...



(sorry for hijacking)

 

[frolf]

I drove my 325i in MN winters 2 years, it sucks balls. I got stuck every day. I would definatly put a LSD in if you plan on driving in snow.

Where in MN are you?

you disappoint me

 

[echothreezero]

here in Australia, we have NSD (no slip diff)...

we just weld 'em up...

Hah! we have those too except they are reserved for two types of cars:

Those owned by race-car drivers

Those owned by retards

Welding your diff for street use is plain stupid - you wear out all your other components faster and it makes your car a bitch to steer at low speeds. Good for burnouts tho.

Put the LSD in. Snow or no snow - regardless, LSD is the superior option.