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.

 

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.

 

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.

 

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.

 

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.

 

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

 

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

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.

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.

 

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.

 

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

 

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.

 

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.

 

Corner exit speed is worth more then straight line acceleration because very few tracks have long enough straights to allow a competitor to make up the corner exit speed difference before braking is required for the next turn.

If car A comes out of the corner with a 5 mph speed advantage, car B needs to:

1. Make up that speed difference to stop losing ground to car A.
2. Accelerate at a faster rate then car A to gain back the gap.
3. Pass car A (a lot harder then most people think).
4. Out brake car A to the next turn from a higher rate of speed.

All the above must be done within the confines of the straight and usually in less then 15 or 20 seconds.

 

John has a very important point that we should emphasize here. Assume you come out of Turn 9 at Willow Springs International Raceway at 100mph +, on to the front straight of one half mile length. You will reach a top speed in many cars at 145mph and in some cars at 170mph +. The straight will be consumed in less than 15 seconds at that range of velocities. A car with a 5mph advantage in corner exit speed, and the power that is required to overcome it.......tough to do. Especially if he is pulling you coming out of the corner. Unless you were passed right at corner exit....an almost unthinkable event given that particular corner, your chances of making up the difference are pretty slim even on a half mile straight, your best passing zone. Driving the corners is what HPDE is all about. It is why good drivers in spec Miatas beat modest drivers in Vipers and Vettes all day long.

 

Dave,
Yes, please bring your 550# springs. I don't plan to swap them there at the track, but would like to try them out if my camber and air pressure adjustments don't work out. I'll be back at Thunderhill with HOD on 9/19 (I think you were planning on doing this one too) and again with NCRC on 9/26. I should have plenty of opportunities to dial things in.

Yes, understeer from apex to exit, but enough that I think my front tires wear slightly faster or at the same rate as the rears. Any counter steering originates from my desire to alleviate excessive scrub to the front end. I thought this was normal until I got a ride in that Turner Motorsports 325i race car, then...I found out that my car is not behaving quite like that.

 

I mean... soften the front sway to work against undesteer.
I can understand putting stiffer springs if your front external wheel goes a lot down.. than you'll get understeer because a lot of weight is shifting there instead of staying in the rear.
to me that causes really sudden reactions. sometimes I miss the stock vlsd for how was easy to "turn" but then I remember how the car feels "floating" and I just get the next apex a little bit later
mine at -2 is eating the shoulder block and pretty even inside... I'll go at -2.5 (my previous Z was -2.7 F and -2.2 R and was almost an oversteer monster )

 

If this thread was started because your car doesn't handle like Turner Motorsport's world challenge car driven by a pro driver, than I vote to ban you

 

After reading my statement again, I feel like banning myself he he he...Yeah, I know it seems unfair to compare, especially since I'm running one of the most inexpensive suspension setups available, and is currently being tuned by a hack (yours truly). I probably should clarify myself...I just want grip to be a bit more neutral under throttle; vaguely similar to my experience in the Turner Motorsports car. Does that sound more reasonable?

BTW, After 10 years of owning a Specialized FSR mt bike, I finally got my suspension dialed in. Apparently, I needed a new front fork AND rear shock, and about 20 minutes of testing and tuning by going over sidewalk curbs. I don't know why I tried to live with the crappy OE fork and shocks...10 years. I certainly want to get this car handling right, and be done with the tinkering.

 

Let me hear your thoughts.

 

I ran one in my 951, good stuff. IF you can afford to wait, talk to Torvec - the stuff I've heard (and now seen in person, toured the place since they happen to be local to me) is AMAZING...