Temple

I'm about to add an LSD to my 993 and I was wondering what lockup percentage people would recommend. I've seen 25/65%, 40/65%, 40/80%, etc.

I drive my 993 C2S daily, and do a handful of DE events every year.

After reviewing the archives and talking to various folks, I've already decided to go with a Guard LSD and the clutch type (not the torque sensing/Quaife type).

But I have no idea what percentages I should purchase. Any thoughts or advice?

Greg Fishman

Why not go with a Torsen Bias diff if it is your daily driver. A clutch type diff will just induce more understeer and not give you as much grip under acceleration. Do you have a way to dial out more understeer?

David in LA

Temple - Which shop is doing the work, or is this a DIY? Just out of curiousity and for my future referernce in case I do this mod at some point.

TIA

chris walrod

I assume the first number is for accel and the second number is for decel. The 40/80 is more than likely the angle of the 'ramps' inside the diff that dictate how much clamping is applied to the clutch packs. So 40 on accel would be pretty agressive, while 80 on the decel would be more mild, or less pressure applied to the clutch packs. The more pressure applied to the clutches results in more understeer.

In most modern open wheel race cars, the ramps are reversable so tuning is possible. Of course this isnt so ideal for a road car as its a lot of work to change them around.

I would think the 40/80 would be the best choice. The best thing to do is decide what you want to do with the car, and speak to people that have used this type of diff.

Sorry to get carried away with this. Just want to share my experiences with this type of diff.

Martin S.

Written by Temple above, a person of great fortune living in the Mecca of Porsche High Performance Shops, Southern California. Temple writes, "I'm about to add an LSD to my 993 and I was wondering what lockup percentage people would recommend. I've seen 25/65%, 40/65%, 40/80%, etc.I drive my 993 C2S daily, and do a handful of DE events every year."

Now you have me wondering and I have gotten out the old <img border="0" alt="[soapbox]" title="" src="graemlins/soapbox.gif" /> . If you do a handful of DEs per year, there are a lot of other things you can do to get performance out of your car in contrast to adding a limited slip. Keep in mind, you'll be paying $1,500 to $2,000 just for the LSD, and 15 to 20 hours of labor to get it installed and set up correctly <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> . Don't take my word for it, poll shops in your area as to their estimate of the job, parts and labor.

If you want some zip around town, install a lower (higher numerically) ring and pinion gear. You get approximately 16% better gearing (better acceleration). You'll be a star at your local DEs pulling your colleagues out of the corners <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" /> . Your cost should be somewhere in the neighborhood of $3,500...with the change left over, buy a chip for your car, about $1,000 for approximately 15HP.

However, if you have decided to purchase and install a LSD...first get an education from an article mentioned below and seek out opinions of performance orientated shop owners whom you know and trust <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" /> .

If you want an education on Limited Slip Differentials (LSD) somewhere get a copy of the Porsche Owners Club Magazine, Velocity, February 2001. There is an excellent article on LSDs penned by Greg Brown, owner and head wrench at Precision Motorworks in Anaheim Hills, CA 714 879 9072 or Gregbbrd@aol.com <img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" />

IMHO, and in my research, for me, there are only two choices, the Porsche Motorsports LSD, a clutch pack style, with 45/65 stated in Greg's article. They are available for about $1,500 and approximately 20 hours of labor to install them correctly: This is what has been told to me by numerous mechanics. Mind Over Motorsports in San Diego (858) 693-9911 info@mindovermotorsports.com recommends that their customers employ the Porsche Motorsports LSD if they are inclined to purchase only "factory" products, but are the first to admit that the Guard Transmission (GT) is extremely rugged and well built, and recommend the Guard unit as well .

The Guard Transmission (GT) LSD, also a clutch pack style, available with dual ramp angles, according to GT, "allows a choice of two locking ratios. You can have a 40/60 // and/or a 50/80 set up with one unit, or a 50/80 // 80/80 set up with the other unit. Hergie at Hergersheimer Motorsports, Lake Forest, CA +1 (949) 458-7223 is a big proponent of the GT LSD . Paul Guard has a very large group of folks that swear by his product. It is extremely well built and rugged.

Why not the Quaife/Torsen? IMHO, I want a LSD that will lock up the rear end on trailing throttle. To my knowledge, if this happens with the Quaife, it is insignificant compared to the Guard or the Porsche Motorsports.

Also note as posted above, if you install a gut wrenching, rock solid LSD such as the Porsche Motorsports or Guard Transmission (GT) LSD, you will find that you may have a car with more pronounced understeer <img border="0" alt="[nono]" title="" src="graemlins/nono.gif" /> . You may need (probably will need) adjustable sway bars to dial out the understeer. Price out 993 adjustable sway bars: You are looking at a $1,000 + expense, plus installation <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> .

If you are going to add a LSD, do it because you want more dig out of the corners, you want to eliminate excessive wheelspin and you want the car to be solid upon deceleration. For most of us, seldom will we encounter a situation on the street where you will be confronted with these situations, to the extent that it makes sense to drop $4,000 into a LSD.

Adding a LSD may serve to solve some problems, but while in the process, create new problems that require expensive solutions. There are no cheap fixes on a 993 car .

Do your research and be certain the LSD is what you REALLY want. I know I do, however I will not install one until I have adjustable sway bars and a new coil over suspension, ouch!!!

Paul

The various lock-up figures are defined by Porsche as "percentage of anti-slip effectiveness". They are just relative figures --- nothing precise. The shallower the ramp angle, the more easily the crosshafts slide up spreading the pressure rings, thus corresponding to a higher lock-up figure.

40/60 is probably the most popular selection for a NA 993, while the GT3Rs prefer 50/80 or sometimes 80/80.

While most marques use reversible ramps, Porsche design specifies a one-way-only installation, almost always opting for greater lock-up on deceleration.

DJF1

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Martin S.:
<strong>
Also note as posted above, if you install a gut wrenching, rock solid LSD such as the Porsche Motorsports or Guard Transmission (GT) LSD, you will find that you may have a car with more pronounced understeer <img border="0" alt="[nono]" title="" src="graemlins/nono.gif" /> . You may need (probably will need) adjustable sway bars to dial out the understeer. Price out 993 adjustable sway bars: You are looking at a $1,000 + expense, plus installation <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> .

</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I will confirm what Martin says... I installed a Porsche Motorsports LSD on my race car and the car understeers like a pig! <img border="0" alt="[grrrrrrr]" title="" src="graemlins/cussing.gif" /> Still playing with the sway bars, tire pressures, spring rates etc. No wonder I was scratching my head why on earth I was slower with the race car than with the cabrio. I just could not figure out what so went wrong and the car understeered so badly compared to the first outing of the car in early march... Now I know <img border="0" alt="[grrrrrrr]" title="" src="graemlins/cussing.gif" />

Paul

Yes, unless you're prepared to stiffen and tune the suspension, you're probably better off with the torque-biasing differential.

Temple

Wow, good stuff so far. Guess I should have given some more background in my initial post. Sorry for the long-windedness, but maybe this will help others that are thinking of going down this path...

Recently, my transmission began to leak. Every day I've got a bigger puddle of oil under my parking spot at home and at the office. So now I have to pull n' reseal my tranny.

So I searched the trusty rennlist archives and have seen what folks recommend to do once you go through this fairly expensive procedure (e.g., replacing various sensors).

Of course, once the tranny is pulled it appears there are all sorts of potential fun, uh, what's that word . . . oh yeah, UPGRADES!

So for the past few weeks I've spoken to Weiner, Andial, Hergie, various rennlisters, and searched the archives (incl. the perf. & mod. and 993 turbo archives as well). I've priced out RS clutch/LWF packages, euro trannies (thanks Harald!), R&P, LSD, custom gearing, etc.

At the moment, I plan on upgrading with an RS clutch/LWF, adding new 3-5th Guard gears, and an LSD.

I have shied away from the R&P as most seem to believe it is useful if you do it in conjunction with new gears, but as a stand-alone upgrade it a) doesn't address the RPM drop between gears, b) renders 1st fairly useless, and c) might create some noise issues. I do have a C2S, so I know this is a valid option on my car but I don't know of anyone that has done solely a R&P swap so I'm hesistant to choose that over new gears (especially with so many folks counselling against it).

The weak dollar is effectively making a used g50/21 tranny an uneconomical option compared to new custom gears. I have driven Viken's car and definitely noticed it felt much stronger (it has a euro tranny and RS Clutch/LWF). So while I won't get a new 2nd gear, 3-5th will be much tighter and more aggressive. I'm still debating whether to move my stock 5th to 6th or retain my 6th as is -- I'm leaning toward leaving my 6th gear alone as an overdrive for highway cruising (even if it makes for a large gap between 5th n' 6th).

What else? RS/LWF -- I have a 97 so my computer should take care of stalling issues, and I'm prepared to live with (hopefully enjoy) the 'chatter' at idle in exchange for quicker reving. I could go another 40K miles, probably, on my current clutch, but, again, figure I might as well do what I can while the tranny is out.

And, finally, the LSD. I've read the Velocity article on LSD (claiming its worth an average of 2 seconds on most tracks) and everyone seems to think I'd be better off with one than without. The general impression I've been given so far is that the quaife/torsen type are for autocross/street but that those who installed one and went on the track eventually 'upgraded' again to the clutch-type. Advantages of the quaife/torsen are a) no maintenance, b) no effect on current handling setup. Disadvantages are no assistance under braking -- it only kicks in when you are on the gas.

The clutch-type (which is more expensive, btw) does require some maintenance, and will add understeer to your car, but does provide lockup under braking so its much better for the track. My concerns on this type of LSD have been how much maintenance is required (so far, doesn't sound that serious) and how much it affects handling. I guess one of the reasons for my initial post is that I was thinking maybe certain percentages will lessen the understeer impact. Frankly, y'all are making me think that if I go with the clutch-type LSD I'm about to reverse all the nice handling improvements I've made with bigger sway bars and find I've got an understeering pig.

Given that my larger sway bars are nonadjustable, maybe I would be better off with simply a quaife/torsen type LSD. Or, and this is my bank account insisting I ask this, maybe I can skip an LSD altogether. Has anyone installed either type of LSD and decided it really didn't do much?

Finally, I'm getting my work done by Tony at <a href="http://www.callasrennsport.com/" target="_blank">Callas Rennsport</a>.

Thanks again for all the advice! <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

tom_993

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Martin S.:
<strong>
If you want an education on Limited Slip Differentials (LSD) somewhere get a copy of the Porsche Owners Club Magazine, Velocity, February 2001. There is an excellent article on LSDs penned by Greg Brown, owner and head wrench at Precision Motorworks in Anaheim Hills, CA 714 879 9072 or Gregbbrd@aol.com <img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" />
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">That article can be found here: <a href="http://www.porscheclub.com/pdf/2001/february.PDF" target="_blank">http://www.porscheclub.com/pdf/2001/february.PDF</a>

There are some more (basic) LSD articles here:
<a href="http://4x4abc.com/4WD101/limitedslip.html" target="_blank">http://4x4abc.com/4WD101/limitedslip.html</a>

and here: <a href="http://auto.howstuffworks.com/differential.htm" target="_blank">http://auto.howstuffworks.com/differential.htm</a>

Tom
'95 993

Martin S.

After reading above,"At the moment, I plan on upgrading with an RS clutch/LWF, adding new 3-5th Guard gears, and an LSD."

If you are "investing" that amount of cash in repairs, just drop in the PSS9s and RS sway bars while you are at it. The PSS9s are 9 way adjustable. You can set them on the softest setting for the street .

With the tranny upgrades and the PSS9s, your DE events will be very enjoyable ...you mantioned only doing a few per year. I suspect if you set the car up as described above, the "Hook" will be set and you'll do more than a "few" DEs annually.

The tranny "repairs" you are doing, and the suspension are 2 out of the 4 biggest payoff "repairs"/modifications you can do. Don't forget a (3) racing seat with the 5 or 6 point belts and a (4) set of sticky tires on 18" wheels. This would be a home run in L Production class in POC. Couple all this with a little driving skill, you could be <img border="0" alt="[king]" title="" src="graemlins/r.gif" />

Good luck with your "repairs". It is clear you have done your homework...now I had better do some work or I be out on the streets <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" /> !

Tom W

Temple,

About 1.5 years ago I had a tranny problem and took the oportunity to upgrade while everything was pulled apart -- regear 2-6, Porsche LSD, RS LFW. This was all just before I started autocrossing.

I think I now know why my car subsequently understeered like a pig. It was so bad that no matter what we tried I could not get the car to trail brake and release the rear end (of course since I had never done it before, it was difficult for me or my instructors to understand why not).

I recently upgraded to PSS-9's and RS bars and a more aggressive alignment (RS spec). At first I left the RS bars set in the middle and still had bad understeer for autox and my first DE. I subsequently firmed the rear sway and found I have a whole new car -- the understeer is gone and I actually can get the *** end around in tight corners. It took about 5 autox runs before I started to get the hang of the new handling. I'm looking forward to Thunderhill in two weeks to see how it does on the track with this suspension setting.

So, my advice is that the mods you are considering will be fun, but will fall short of what you probably want until you add the suspension and sway bar change. By the way, my car is also a daily driver that sees autox and some DE. The improvements are noticable when compared to stock cars (hell, for that much money, they better be).

{edit} My LSD is the one that could be ordered as an option for our cars (I believe it's 40/60). I added it instead of a Guard clutch type due to expense - it was cheaper.