What do you guys know about LSD's?

[dnguyent]

Here's an interesting article about LSD's:
http://www.guardtransmission.com/velocity.htm

Sorry it's mostly geared towards rear engined Porsches, but I found the article very interesting, and it confirms how little I understand about how these units affect handling.

FYI, I went from the OE viscous unit to the Cusco RS set at 1.5 way and 80% locking. I think Porsche would call this a 80/40 LSD setting (80% locking under acceleration/40% locking under deceleration), which seems to be vastly different than what they spec their track/race cars with (45/65, 50/80, and 80/80).

A couple things I noticed when I upgraded to the Cusco unit:

1. More consistent lockup on exit, especially noticeable on sharper turns.
2. More understeer on throttle application. I'm trying to find a way to reduce the amount of understeer with alignment/sway bar adj/different springs/track width as I'm already running a square tire setup.
3. Very stable off throttle and under braking. In fact, the car no longer responds to throttle steer. I'm also considering changing my driving style a bit to take advantage of the cars resistance to off-throttle spinning like braking further into turns.

[Slow*Jim]

Good read, thanks for sharing.
Once you get the suspension dialed in, post up your specs and settings! I'm sure your lap times will improve quite a bit.

[betamotorsports]

Power on understeer means you need to increase grip in front.

[Eagle1]

Originally Posted by betamotorsports

Power on understeer means you need to increase grip in front.

Especially if you are running same tire size all around.

Try to increase the amount of negative camber you are running up front as well, if you have not done that already. -2.5 degrees might be a good starting place.

[Gsedan35]

Originally Posted by Slow*Jim

Good read, thanks for sharing.
Once you get the suspension dialed in, post up your specs and settings! I'm sure your lap times will improve quite a bit.

Last time I heard he was running OTS Koni Yellow's with Tom Motorsports coilovers 500/500.

[Gsedan35]

Originally Posted by dnguyent

Here's an interesting article about LSD's:
http://www.guardtransmission.com/velocity.htm

Sorry it's mostly geared towards rear engined Porsches, but I found the article very interesting, and it confirms how little I understand about how these units affect handling.

FYI, I went from the OE viscous unit to the Cusco RS set at 1.5 way and 80% locking. I think Porsche would call this a 80/40 LSD setting (80% locking under acceleration/40% locking under deceleration), which seems to be vastly different than what they spec their track/race cars with (45/65, 50/80, and 80/80).

A couple things I noticed when I upgraded to the Cusco unit:

1. More consistent lockup on exit, especially noticeable on sharper turns.
2. More understeer on throttle application. I'm trying to find a way to reduce the amount of understeer with alignment/sway bar adj/different springs/track width as I'm already running a square tire setup.
3. Very stable off throttle and under braking. In fact, the car no longer responds to throttle steer. I'm also considering changing my driving style a bit to take advantage of the cars resistance to off-throttle spinning like braking further into turns.

Thanks for posting, especially your owner comments about having the Cusco RS. I've been considering that LSD.

[daveh]

I suggest you take yours apart 3 times like I did to change settings

One thing that helped me realize the effects of a limited slip was driving on track in the rain. I really felt the on-throttle understeer with the limited traction of the front tires.

Perhaps the 45/65 numbers the article (that I haven't read) refer to are ramp angles. BMW's commonly use ramp angles of 30/90 to tame understeer. It's a different feel than our lsd's in that it takes much more torque to get to full lockup. Different ramp angles are the equivalant to a 1 / 1.5 / 2 way as the japanese lsd's. I'm sure different platforms work better with different ramp angles and breakaway settings.

[mw9]

nice info, thanks for the post

[Eagle1]

IF you are going to be running NA, and go to the track only occasionally, you might want to consider a torsion sensing (Torsen) screw type lsd. They are very quiet and smooth, and thus in daily driving applications very civilized. The clutch type mechanical lsd unit, like a Cusco or Nismo, is a "bad boy" that will chatter and chirp and grab in slow speed tight turns in parking lots and intersections. For the hard core high power application, however, I would not recommend it. Quaife makes a nice unit that fits our cars, if that is of interest.

[betamotorsports]

OS Giken also make a nice clutch pack unit. Its very adjustable (out of the car) and has two basic settings - S (Standard) that has a lower preload for street driving and another setting (don't know the term) that is more race oriented. The diff is basically a 1 or 1.5 way but that's completely adjustable.

I'm running one in my 350Z at the race oriented setting and its much smoother in power application then the Nismo unit I ran previously.

[dnguyent]

Originally Posted by Eagle1

IF you are going to be running NA, and go to the track only occasionally, you might want to consider a torsion sensing (Torsen) screw type lsd. They are very quiet and smooth, and thus in daily driving applications very civilized. The clutch type mechanical lsd unit, like a Cusco or Nismo, is a "bad boy" that will chatter and chirp and grab in slow speed tight turns in parking lots and intersections. For the hard core high power application, however, I would not recommend it. Quaife makes a nice unit that fits our cars, if that is of interest.

I plan to keep my engine NA and relatively stock (powerwise). The car sees the track ~20-25 days/year and is no longer used as a DD due to a growing family and its inability to carry my road bike (my true daily driver). If I wasn't taking this car to the track, I would have sold it by now. I don't even bother swapping in street pads and tires anymore. For the price and the car's intended use and power levels, the Cusco RS/Nismo units are hard to beat.

I've been very happy with the engagement of the Cusco RS unit. Yes, the tires chirp in slow sharp corners, but the unit doesn't chatter. It might be due to the WPC treatment of the clutch discs prior to installation. I'm also running the Motul 90PA fluid. When I was using the Valvoline High Performance Gear Oil, the LSD was a bit more jerky.

I've upped the front-end negative camber from -2.6 to 3.0 to see if I can get a bit more grip out of the RA1 tires. The rear seems to be gripping and wearing well at -2.2 camber. We'll see how it goes this weekend. If the changes do not work, I'll stiffen my front Hotchkis sway bars from med to stiff. This step puzzles me because it should technically decrease my front end grip, but a few respectable individuals have had success with running a stiffer sway setting up front.

If that doesn't work, I'll increase my rear ride height to add some rake into it. It is currently adjusted for equal static height as measured from the ground to the chassis seams. I'm thinking that rear squat under acceleration is causing the rear end to be lower thereby adding a bit of front end lift under med/high speed corners. OE calls for a slight rake (~1/2" higher in the back). The car exhibits a nice 4-wheel drift on slower corners (ie T14 at Thnderhill), so maybe aerodynamics is coming into play here.

If that doesn't work, I'm going to increase my front springs to ~600#. This step comes from a Carrol Smith book, AND it works well for daveh. If that doesn't work, I'll add a front splitter. And, if that doesn't work, I'm going to take Daveh's suggestion and take apart the LSD to change the settings --->60% locking (eek!). This is my last step because it seems that rear end grip is very good, which is causing front-end problems....but in the end, I prefer a balanced and well sorted car over one that has the more overall grip but pushes.

G35Sedan is right, and I'm using OTS Koni Yellow with Tom Motorsport springs (500/500). These spring rates are 'published', but not verified. I'm maxed out on rear end rebound, but have some more rebound adj on the front if I need to add more.

[mw9]

What Carrol Smith book are you reading this from, I saw he had a few. On your cusco Rs, how hard is the install and changing settings on it.

[Ataru074]

Originally Posted by dnguyent

If that doesn't work, I'm going to increase my front springs to ~600#. This step comes from a Carrol Smith book, AND it works well for daveh. If that doesn't work, I'll add a front splitter. And, if that doesn't work, I'm going to take Daveh's suggestion and take apart the LSD to change the settings --->60% locking (eek!).

Let us know.. because looks like all those suggestions goes in the opposite direction.
the first I'll try would be to soften the sway bar. even before touching height, springs....

my cusco is at 100% and I have a pretty nice push.. but as I put a stiffer springs in the rear it's working better... than I made the mistake of lowering the front... more understeer.. so, put the rear at the same height... better.

if you have aftermarket swaybars I'd try also to lower the front camber a little bit.. (back to -2) maybe you just can't "load" the wheel before having that angle start working.

for me is working pretty well for the added stability.... brake more into the corners, go to the apex a little bit later and than use the full traction to exit as a rocket and is incredibly easy to control if the rear gets a little loose in 3rd gear.

[dnguyent]

Originally Posted by mw9

What Carrol Smith book are you reading this from, I saw he had a few. On your cusco Rs, how hard is the install and changing settings on it.

The Carrol Smith book is actually a small reference guide: "Engineer in Your Pocket"

[dnguyent]

Originally Posted by Ataru074

Let us know.. because looks like all those suggestions goes in the opposite direction.
the first I'll try would be to soften the sway bar. even before touching height, springs....

Actually, from what I've read, softening the rear is supposed to add more grip to the respective end.

Originally Posted by Ataru074

my cusco is at 100% and I have a pretty nice push.. but as I put a stiffer springs in the rear it's working better... than I made the mistake of lowering the front... more understeer.. so, put the rear at the same height... better.

Yeah, that's certainly opposite of what I was intending on doing. But, maybe lowering the front end, thereby lowering the roll center, causes understeer. I'll have to check on that before I mess with the ride height.

Originally Posted by Ataru074

if you have aftermarket swaybars I'd try also to lower the front camber a little bit.. (back to -2) maybe you just can't "load" the wheel before having that angle start working.

for me is working pretty well for the added stability.... brake more into the corners, go to the apex a little bit later and than use the full traction to exit as a rocket and is incredibly easy to control if the rear gets a little loose in 3rd gear.

At -2.0 at the front, the outside shoulder blocks of my tires shows quite a bit more wear. No doubt braking will be affected, and I'll just have to see if the added lateral traction is worth the loss in braking prowess.

[first350]

I also have the Cusco RS 1.5way @ 80% lock - I absolutely love it! I run BSP for autoX, so my application is a bit different compared to track days...but I would say it's been one of the best additions to my Z - I only wish I did this as my first mod rather than my last!

*if you're worried about understeer, go w/ a 295 R-comp up front

[Eagle1]

Originally Posted by first350

I also have the Cusco RS 1.5way @ 80% lock - I absolutely love it! I run BSP for autoX, so my application is a bit different compared to track days...but I would say it's been one of the best additions to my Z - I only wish I did this as my first mod rather than my last!

*if you're worried about understeer, go w/ a 295 R-comp up front

Adding more rubber up front will give more grip, but only to a point. There are other factors to consider when you get to those extreme sizes, including the unsprung weight impact on acceleration, braking, turn in, and your spring/damper settings, ride quality (transmission of NVH), and the certainty of your having to install a power steering cooler if you run that much tire up front on a road course car. On a twisty track you will almost certainly start boiling your PS fluid with tires at 275 treadwidth and above, when driven hard on the Z and G.

[Lawn Dart]

Power on understeer means you need to increase grip in front.

With the LSD, he has too much rear grip. He also needs to increase his rear tire pressure.

[first350]

Originally Posted by Eagle1

Adding more rubber up front will give more grip, but only to a point. There are other factors to consider when you get to those extreme sizes, including the unsprung weight impact on acceleration, braking, turn in, and your spring/damper settings, ride quality (transmission of NVH), and the certainty of your having to install a power steering cooler if you run that much tire up front on a road course car. On a twisty track you will almost certainly start boiling your PS fluid with tires at 275 treadwidth and above, when driven hard on the Z and G.

that makes sense to me...since I have a set of dedicated autoX tires, I dont' have to worry about most of those things - my main concern was being able to get enough heat in them. IMO lots of setting can be sharted between autoX and track days for dual purpose cars...but when you start to get focused on 1 application, settings need to be taylored to what you're doing.

I run a F295/R315 for autoX...I would assume that on a track, I would have slower times b/c the gain in grip for the corners would not out weigh the penalty in the straights.

[daveh]

I wasn't totally serious about taking apart your lsd. 80% should be good for track use. I just wanted someone to feel my pain

I think you're on the right track beginning with camber (and making only one change at a time). I'll be at the track this weekend and can help you take some temps to attack this more scientifically. I can bring some of my spare front springs too if you really want to get dirty.

Also after reading your complaint about push upon throttle application, this describes understeer from apex to exit - correct? A little of this is ok in my book unless it's too excessive since it's happening in the unwinding phase of the turn.