lsd help..

[lodgy]

thinking of fitting a lsd but all the adverts list differant ratios and im not sure which would be best. its going on a 320i e30

all help appreciated

Edited by lodgy on Tuesday 16th September 07:29

[crofty1984]

Depends on what you're after.

First find the ratio of the diff that's on your car at the moment.

If you like it the way it is, then buy an LSD that matches the ratio exactly (or as close as possible)
If you'd like more accelleration at the expense of top end speed (and fuel economy when cruising) then get one with higher ratios (ie 1:1.75 is higher than 1.5)
If you'd like a higher top speed (or perhaps more relaxed cruising) then get a lower ratio diff.

I'm afraid I don't know what is available for your car specifically, but that's the engineering behind it.

[lodgy]

thanks thats helped alot

next question, how do i find out what mines running at the moment and if i get a lsd diff with a high ratio like 4.10 how much will it affect my top speed???

Edited by lodgy on Tuesday 16th September 10:38

[E30M3SE]

lodgy said:

thanks thats helped alot

next question, how do i find out what mines running at the moment and if i get a lsd diff with a high ratio like 4.10 how much will it affect my top speed???

Edited by lodgy on Tuesday 16th September 10:38

If you look at the diff on the car at the moment there should be a metal tag on it with a letter & numbers eg, S 3,64 844, this means. S= LSD, 3,64 is the ratio.

Take into account the wheels and tyres that you are using.

[lodgy]

so what does the ratio actually mean???

[E30M3SE]

lodgy said:

so what does the ratio actually mean???

It's the number of turns of the pinion v's the crown wheel.

The 320i's have 4.10 ratio diff, so that is what you need to find with an LSD if you want everything to remain as it is.

[crofty1984]

top speed?
Max revs x top gear ratio x diff ratio = rotations of the wheel (you REALLY should use SI metric units for this!!)
For every rotation of the wheel you will cover Pi x d where d is the outside diameter of the wheel and tyre.

From that info you can easily convert m/s to MPH

(showing off now)
That's of course assuming the engine produces enough torque at that point.

Tw=Te x (transferred moments of inertia)

[crofty1984]

lodgy said:

so what does the ratio actually mean???

If I remember correctly (and it's possible I don't!) The reason you have a diff at the back with ANY ratio that's not 1:1 is so that you can have a thinner propshaft, so your propshaft will turn 4.1 times (with a 4.1:1 diff) with low torque and a more delicate propshaft, that will turn the wheels with a greater torque (and therefore more sturdy shafts) once.

[gizlaroc]

Loads always for sale on www.e30zone.net forums.