What sized slipper for Cinderella?

[doggydoo2000]

Hi,

I've looked through the posts but just want to check with someone who really knows - which lsd is best for 4 door 325i for track & hill climbs?
I believe from the posts its the 3:91 - can anyone with experience confirm or advise

Thanks

[doggydoo2000]

anyone?

[Brian28]

It depends. You are aiming for a ratio that will give you the right gearing for the corners, ie something that gives you good drive out of a corner and there is a "right" gear for each corner, rather than finding out that a corner is a bit too quick for 3rd but not quite quick enough for 4th etc, something that lets you drive out of a corner and get straight again before you need to change up, etc. Lower gearing (higher number on the diff) will give you better acceleration off the line, but isn't necessarily the best for the track layout you are using. Trial and error, unless anybody else with an E30 is doing the same tracks and can advise on how the car is geared and if higher/lower would suit better. Even then it would probably be different unless the cars are set up the same, similar torque curve etc. Back to trial and error

[doggydoo2000]

Cheers Brian. Well its not for any particular track/hill climb but I can see the value now in certain tweaks that you can do for specific tracks etc.

So for general track & hill climb should I plumb for 3:91 or a 4:10

Anybody got any experience or recommendations?

[Brian28]

4.10 would be my choice, better accelleration overall and its very unlikely that you will be topping out.

[DAV3]

I have just replaced my 3.64 open diff for a 3.91 lsd in my 325i sprint car,(standard se gearbox) and have to say it's bang on reducing my lap times at Curbrough sprint circuit to within 0.30 of the 3.0lt E36 M3's and matching or beating the initial acceleration of most in the paddock.

Dave

[doggydoo2000]

so 1 vote for each! I like the sound of the 4.10 quick off the mark but what are the drawbacks?
Any more voters?

[DAV3]

Download the speed calculator from http://www.quaife.co.uk/, helped with my decision

Dave

[doggydoo2000]

what did you plumb for dav & why?

[Brian28]

so 1 vote for each! I like the sound of the 4.10 quick off the mark but what are the drawbacks?
Any more voters?

On a track with a fast corner leading on to a long straight, the car may top out (be revving past the useful rev range in 5th). Not many tracks where this is likely tho, possibly Snetterton, possibly Thruxton? But Thruxton seldom do track days anyhow.

[DAV3]

I chose the 3.93 to get the best comprise between acceleration and top speed in a given gear particularly 2nd and 3rd which are well used in the sprints I do. My mildly tuned 2.7 SE was quicker off the line than the 3.0 & 3.2 E36 M3's and a new E92 M3 at yesterdays sprint at Curbrough . I just need less weight more power, as well as some more negative camber to beat them around the rest of the circuit!

Dave

[gareth]

afaik, the only standard E30 4.1 LSD will be a small case jobbie. i'd go for a medium case (stronger) 3.91. both are interchangable.

[doggydoo2000]

Thanks guys

Yep Gareth thats what I'm going for - the 4:10 sounded worth a try just for fun tho!