LSD or Open Diff for trackday car?

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GuyM
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Wed Jul 25, 2007 2:52 pm

I have a good LSD on at the moment which does the job fine on my '87 325i Trackcar.

Considering a 4.45 Open Diff offered by another zoner but just want a bit of advice/input.

I'm not too worried about top speed (can't get beyond about 110mph on most straights anyway) but would a 4.45 make a significant/noticeable difference to my acceleration - or would i not notice it that much and lose out significantly on top speed?

also are the driving characteristics of the car going to change much - and if so how? (eg corners/wet/sliding etc)

any advice much apprecieted - i'm a bit of a novice at this!
karaokebykris
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Wed Jul 25, 2007 3:04 pm

Acceleration will be greatly improved with a 4.45 diff, I have really noticed the difference since going from a 4.45 to a 3.64 slipper acceleration wise. Car seems less raw now if you know what i mean....

traction wise i could not comment as I have not driven it in anger since having the lsd in there
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JungleGus
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Wed Jul 25, 2007 3:10 pm

what ratio is the LSD?

defintely stay with the LSD...open diffs suck

the 4.45, is it a med or a small case? (4 v 6 bolts) i can show if someone posts a pic up i dont have any handy

if it is a medium (what your LSD likely is) you can swap LSD centres

4.45 is a decent ratio, a mate has one on his race car, quite short but it works well..i think he locked it if i remember rightly. it is v short for the road though, i found 4.1 short on the road when i tested one...so depends how much road driving you do as well
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GuyM
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Wed Jul 25, 2007 6:28 pm

the car is just for the track. the only road driving i do in it is to and from the track!

karaokebykris - yes its your one for sale that i'm thinking about!....i think you said it was a small case so i am hoping i can just swap it for my LSD - and always go back if i'm not happy!

My current LSD is a 3.64 (off a 325 sport I think) and feels good, so what handling differences will i notice if i go from an LSD to an Open Diff?
1an
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Wed Jul 25, 2007 6:49 pm

LSD will be much better on the track, i.e you will have more grip, with an open diff you are more likely to spin the inside wheel
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Wed Jul 25, 2007 8:23 pm

if you have a good setup i dont think you will notice alot of diff as weight balance will be good.. my open diff e36 will still 'step out' unda acc out of a bend..

i have a low miles 4.45 :wink: :lol:
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skidmark
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Mon Jul 30, 2007 9:45 pm

Hiya .... I am running a 325i track day car with a 4.45 LSD. The ratio is excellent and being very standard in the engine, it doesn't run out of revs at Donington(even with quite low profile slicks).
The thought of running with an open diff scares the bejesus out of me 8O ..... the car gets very good traction at present and with the LSD locking very positively, there is no doubt that the rear end is going to stay where you put it. I have done the Ford Atlas modification where you add another set of plates ...... this is very recommended and in fact usually quite necessary as many used/secondhand LSD have worn to the point that they will often act like an open diff. We have set the breakaway point to about 70lbs.

Hope that helps.
CHEERS
MARK
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