LSD Options

[Russwhitehouse]

Gents, I would appreciate your opinions on this. I am looking to fit a LSD to my tarmac rally car to be. It is a 1969 2 litre 911 and nearing completion of its conversion from track car to rally car.
ZF units seem to be impossible to find although my local Indy Porsche specialist, who is carrying out the work and has many years of racing experience, rates them as his first choice.
Kaaz don't appear to manufacture anything for a car that early although I might be wrong.
Drexler Motorsport make a unit which can be fine tuned and adjusted in situ, sadly with a price tag to match.
Quaife make a unit using helical gears as opposed to friction plates which looks to be ideal and not too pricey, but is it any good?
I throw the question open to the crowd. If you were fitting an LSD what would you go for and why?

Edited by Russwhitehouse on Saturday 10th January 19:58

[Yellow491]

I am running a swedish diff,its amazing,way better than porsche and others.Its a finer more refined diff,not cheap but worth the money,perfect for rally.
Is your box 901 or 915

[Russwhitehouse]

901.

[Yellow491]

Try xtc in exeter,not cheap but the best.

[Russwhitehouse]

What are their contact details?. I can't find them online with just XTC Exeter to go on.
Cheers.

[Yellow491]

Exe-tc.co.uk
I thought you would know them if you are into rallying

[Russwhitehouse]

Not unless they have a branch in the south of France. That's where I live and play.

[V8KSN]

997 GT3 Tarmac Spec LSD from Exe-Tc is £2600

You will have to check with them what the locking ratio is though

[ASM993]

what about these guys?
http://www.guardtransmission.com/

[Russwhitehouse]

ASM993 said:

what about these guys?
http://www.guardtransmission.com/

Already emailed them, no response yet. No european agent either which is going to mean wallet rape by the French in taxes.

[Yellow491]

Sorry did not realise you were out of the uk
Try xtc,better than gaurd.

[wfarrell]

Wavetrac also good option if you don't fancy maintaining a plate LSD

...their design also provides a locking effect on overrun / braking - an advantage over the Quaife

[NJH]

I can't see how it can personally as when both wheels are moving at the same speeds the wavy plates (hence wavetrac) are not going to mesh with each other, the design infers that they only doing anything when there is a speed differential between the two wheels. It should however stop an unloaded inside wheel from spinning up and wasting all the power.

[wfarrell]

NJH said:

I can't see how it can personally as when both wheels are moving at the same speeds the wavy plates (hence wavetrac) are not going to mesh with each other, the design infers that they only doing anything when there is a speed differential between the two wheels. It should however stop an unloaded inside wheel from spinning up and wasting all the power.

Ignoring fully open or locked type differentials, any LSD 'locking action' is a function of relative torque (or rotational velocity) across the LSD output shafts - this is true of plate, wavetrac, or torsen types - although the slip/locking characteristic can vary greatly for each type or application.

Both the plate and wavetrac differential provide a locking effect for both positive and negative torque conditions - this can help prevent individual wheel lock-up under braking and provide enhanced chassis stability, in addition to maintaining traction under acceleration whilst cornering or, if like you it, oversteer :-)

Edited by wfarrell on Tuesday 13th January 23:59

[thegoose]

A guy I know researched this when prep'ing a 915 3.2 for speed events and found a company in Stoke On Trent who made what he wanted (he spec'd it, partly from experience e of his 964RS, he went for some thing a little different to that car's 80/100 (I think) % lock up under acceleration/braking) for a reasonable cost. Their products were only marketed in the USA (not as Guard though) but being local to Cheshire was quite handy for him, particularly as he could go and see them and discuss what he wanted (he's a very particular guy, an engineer himself, so he really liked the consultative approach). I'll see if he has their contact details if you like?

Also, Hartech had diffs made to order for their race cars, they might not want to tell you who by (it was certainly confidential to begin with in 2012) but it's worth calling and asking.

[NJH]

wfarrell said:

NJH said:

I can't see how it can personally as when both wheels are moving at the same speeds the wavy plates (hence wavetrac) are not going to mesh with each other, the design infers that they only doing anything when there is a speed differential between the two wheels. It should however stop an unloaded inside wheel from spinning up and wasting all the power.

Ignoring fully open or locked type differentials, any LSD 'locking action' is a function of relative torque (or rotational velocity) across the LSD output shafts - this is true of plate, wavetrac, or torsen types - although the slip/locking characteristic can vary greatly for each type or application.

Both the plate and wavetrac differential provide a locking effect for both positive and negative torque conditions - this can help prevent individual wheel lock-up under braking and provide enhanced chassis stability, in addition to maintaining traction under acceleration whilst cornering or, if like you it, oversteer :-)

Edited by wfarrell on Tuesday 13th January 23:59

The wavetrac design has plates with a wavy face which don't come into contact with each other unless and until the two sides of the differential are moving at different speeds. In a conventional LSD the plates are pushed together by spring washers (belleville washers) which means there can be considerable meshing of the plates even when the LSD is doing nothing, one can see this when an LSD has stacks of preload because you can put a bar on the output from the gearbox and try and turn it, you may need to put quite a bit of force in to get the thing to break free. In this regard if the wavetrac does indeed provide resistance across the two sides isn't it going to be a bit like a conventional LSD with zero preload?

There are some videos on the net showing the wavetrac doing a convincing job of not chucking all the power into the unloaded wheel which is the thing which really counts, for my own use case I spent 4 years getting the handling to a place where I like it so I specifically do not want the increased understeer under braking which a conventional LSD provides (opposite to 911s who all seem to want this).

[Russwhitehouse]

thegoose said:

A guy I know researched this when prep'ing a 915 3.2 for speed events and found a company in Stoke On Trent who made what he wanted (he spec'd it, partly from experience e of his 964RS, he went for some thing a little different to that car's 80/100 (I think) % lock up under acceleration/braking) for a reasonable cost. Their products were only marketed in the USA (not as Guard though) but being local to Cheshire was quite handy for him, particularly as he could go and see them and discuss what he wanted (he's a very particular guy, an engineer himself, so he really liked the consultative approach). I'll see if he has their contact details if you like?

Also, Hartech had diffs made to order for their race cars, they might not want to tell you who by (it was certainly confidential to begin with in 2012) but it's worth calling and asking.

I appreciate the thought, thanks very much, but how much use my input would be is doubtful. I'm not an engineer and am a long way from Cheshire. Still, might be worth phoning them to listen rather than speak.

[ras62]

I think Marcus is referring to Elite Racing.
http://www.eliteracingtransmissions.com/products/p...

[thegoose]

ras62 said:

I think Marcus is referring to Elite Racing.
http://www.eliteracingtransmissions.com/products/p...

That must be them, saved me a job researching it, thanks.