LSD experiences
 

Now before you hippies start telling tales about the 60's read the questions...

My new 915 gbox with Quaife torque sensing LSD is nearly ready to go in my 2.7RS replica track car.

1. My understanding of the Quaife set up is it will lock under acc'n and release under braking - is this correct or over simplifying things?

2. Would you alter your driving style in any way when using an LSD?

3. Would you alter your car set up in any way (sway bar settings/ alignment etc)?

4. Tips?

Cheers - Ryan

1)It's definitely overly simplistic, but not untrue. I believe that it only locks up as necessary ...

2)Yeah, I'd use more right foot.

3)Yes, but only as necessary. Drive it without changes to see how the new LSD affects the car's overall tendencies ... then make adjustments as needed.

4)Don't take the brown acid ... "It's not poisoned, just poorly manufactured."

Correct, but lock is too strong a word, limit the differential action is more like it. For the track you would also want to do this under braking, as a conventional clutch type ZF will. An 80/100 PMS trans can actually go to full lock under braking, this is good! The Quaife are better suited to A/X than to track use because they don't work on trailing throttle

Under power there will be more understeer, you will need to compensate.



See item 2 above the chassis can be set up to compensate for the understeer which is more pronounced at lower speeds.

Just try to be in a relaxed state of mind when you do it, and in a location free of sirens and stuff. It can really enhance your performance.

Oh, and you'll like the Quaife too.

I've had mine for about 6 months. During normal driving (street), you won't know it's there. I only notice a substantial difference around turn 7 at Road Atlanta and during Auto-x. I expect to notice an improvement at Barber next month coming out of the hairpin and corkscrew. Anywhere you're on hard throttle coming out of a tight corner, you'll appreciate it. I do not notice any appreciable increase in understeer.

Thanks guys - I'll report back when its fitted and given a run.

Cheers - Ryan

Did you do the LSD installation yourself? I was previously given 'thread response' instructions but would appreciate if there is actually a manual/written documentation I could acquire.

Thanks!

Cab - nope, I bought a gbox with a LSD in it, pulled it apart, then gave it to my mech and said "pls put it back together with whatever new bits it needs" It is soon to be swapped for my existing gbox

Cool thing was I assumed it was a ZF (and paid accordingly) but ended up with a Quaife!

Tune in...turn on...er, forget the last part. ;) Given the choice of keeping my orignal ZF or installing a Quaife, no price diff. to me? I kept the ZF, but that's just me...

Once had a lawnmower talk to me. Said my hand was doomed? Now that's LSD!

FTY - A Quaife is not a Limited Slip Differential but rather a Torque Biasing Differential. Both terms are pretty accurate about describing their effects vis-a-vis each other. I agree with the descriptions given above, so I'm not going to repeat them.

None of us can remember the 60's (or 70's and early 80's).
Thank you Mr. Leary.

What? Huh? Had a picture on the wall play cello once. He was playing the overture from Tommy.

Agree, more understeer, you'll just use more gas to compensate. Also agree that the Quaife and their ilk are more suited to autocross than track use. Clutch type is better for a track than autocross.

My understanding is that clutch one is marginally better on trailing throttle and braking but it also wears with time and gradually loses it's diff-braking ability where Quaife unlocks on braking but doesn't have clutches that wear out. Now White Rabbit is probably the best if you can find one...

I agree with Mike above. I swapped out my open diff for a quaife at the same time as a dose of hp upgrade to the motor. I really notice it when stepping on the throttle out of a turn. It really dig's in now.

ZF type LSD's come in different flavors of lockup. The earlier ones only locked up under acceleration. The later ones lock up under acceleration and deacceleration to varying percentages. Depending on the Hp output of your car is how much lockup you want to use. For example, the 917's use a spool thus eliminating a diff. Now for a regular car that would be a waste since most cars don't have the Hp to take advantage of this. ZF's will decrease tire life but if used correctly will drastically reduce laptimes. The added advantage of locking under deacceleration gives the benefit of more stable trail braking in a 911 which in turn allows you to go into a corner deeper. In many ways a Diff should be considered part of the suspension and will need to be considered in the setup.

Cheers, James

Exactly, though I've never heard of a ZF that operated on acceleration only. Lockup %s of from 20-80% are common the former is more street oriented the latter for track only. The newest twist that I alluded to is the different factors on acceleration and decelereation that are available in the G50 and newer diffs. 40/60, 80/100 20/40 etc. are even better on the track.

While it's true that the ZF clutchs do wear, the Quaifes have their own reliability issues. Carrol Smith has advised agaist them for track cars in his Tuning series. Though I think that they are fine even desireable for A/X and street use.

I would go with the ZF because I am a fan of OE ... Quaife might be better, but I personally don't care. JUST MY IDIOTIC OPINION.

Also, the White Rabbit is highly overrated ... I am a BIG fan of Alien Juice (it's a modern thing, don't ask how I know) or Window Payne <-- a friend's mom had some left over.

Also ... tune in, turn on, drop out. http://www.pelicanparts.com/support/smileys/rainbow.gif http://www.pelicanparts.com/support/smileys/explode.gif

Here is an excellent article addressing Porsche Limited Slip Diffs.



Limited Slip Article

Cheers, James