winsome

anyone heard of the 20:80 lsd? how does it compare to the 40:60 lsd?

which one is more suitable for track use?

many thanks!

Winsome

Bill Verburg

LSDs can go from 0:100 to 50:50, the first # is lock up under acceleration and the second in under braking. Which one you want iis variable. Most track setups seem to be 40:60 to 30:70

Geoffrey

C2 production LSDs are 25/65 and C4 are 22/40 lockup. The Motorsports LSD and RS street are 40/65 and Guard Transmission sells 50/80 and 80/80 locking diffs.

samscotts

LSD ratios.
This answer comes from the UK where we race on, as you will already know, tracks with many twisting and varied bends. and some longer ond shorter straights.
I have spent a number of years racing and different tracks need different LSD ratios.
Where longer tracks, which require higher speeds on some straights, a lower geared LSD is preferable and on shorter tracks a higher geared ratio is preferable.
It really is a bit of a suck it and see thing and I have carried up to 4 diffs. with me to various tracks.
Of course a higher geared diff. gives faster off the line speed so it is down to track, tyres, driving styles and reliability variables.
I hope this helps but I'm guessing you all know this already.
Regards. Sam.

Megatron-UK

The 20/80 was also fitted to the 964 Turbo 3.3, the 964 Turbo 3.6 used a slightly different one I believe.

Bill Verburg

Guard also sold 40/60(I have one as a spare/backup) the newer ones are adjustable so you can buy a say 40/60 and later change it.

The 964 turbos w/ g50/52 used 20/100 as did the g50/10s used in the RoW 964RS

911CabSteve

I am currently getting my LSD re-built.. I asked my wrench about the Guard unit and he said the stock 964 unit was very comparable regarding longevity (not sure exactly which 964 LSD model he was referring to)..

He also said the stock 993 LSD clutch pak is not as robust as the 964 unit, the 993 clutch pak being made of a different, fibrous material which flakes off and eventually contaminates all the viscous oil (my situation). Apparently, my mechanic has replaced several track oriented 993 LSD clutch paks with the 964 units with very good, long lasting results, FYI..

Bill Verburg

Stock 964 and 993 LSD has 1 externally splined friction disk sandwiched between an inner concave washer and an internally splined outer plate. The friction coating(2 sides) on the plate is extremely ephemeral. The Porsche Motorsports LSD has 2 externally splined friction disks/side w/ an inner concave washer, outer and middle internally splined plates creating 4 friction surfaces. The friction disks come in various thicknesses. So you can beef up the non PMS LSD by adding disks. You do want to limit preload as too much can induce other problems.

Guard has even tougher plasma coated disks and an even tougher steel alloy case.

The desirable asymmetric lock up was only available on 964 g50/10(RS) and g50/52(turbo) trans and all the 993 transmissions. Porsche achieved this by changing the symmetrical ramps on the thrust rings by cutting a shallower angle on one side allowing the thrust rings to move axially putting extra pressure on the contact surfaces

viperbob

Guard as two units. One that can be 40/60 or 50/80. And another that is 50/80 or 80/80. They have to be removed from the diff and the center section rotated to make the switch. Changing the settings it not something most street drivers really need (and few track guys). The units themselves are unreal and very worth the money.

Megatron-UK

Hah! Well that's me told I knew there was a 20 in there somewhere though