Cool, glad you find it helpful

Back to my poor man's LSD test. If otisdog is right then Porsche finally fix the defective genes that plague the 911's since 996 generation. who knows, maybe they are using VW LSD in the 2010 GT3

Matt, thanks for jumping in to help clarify some LSD concept. I know my rebuild LSD works! ... contrast with what it did and did not do before - nervous rear end under hard braking and not very good "fast out" on exit turn

 

Hello,
As promised here are some pictures for your further review. I'll include captions on them all so it's clear what you are looking at.

This is a worn out plain plate from a 1997 turbo car. See the swirls the friction disc left behind. The following picture is a 996 GT3 that we rebuilt this week. 25k mi on it.

See how the tool marks are still present all in straight lines?
This next picture is the old style friction discs found in the 1997 turbo factory LSD:

Clearly showing wear and signs of biting. Compared to the friction disc from the same GT3 the plain plate came out of:

Practically no wear other than right at the edge.
And just for fun, here's what a Cup Car friction disc looks like (new):

Compared to ours:


Lastly, the other thing I will mention has to do with preload. We absolutely use the preload to assist in tuning the nature of the LSD. This is why you will read some many different numbers from different sources if you wander around the internet. A 914 LSD for a 110chp car gets a different stack and preload than a GT3 like Mike's. And if it's in a dedicated track car like a Cup Car it's a totally different stack and preload from that.

The factory Cup Car (996 version) LSD that I yanked that friction disc out of for the picture was etched with 171.1Nm(126ft/lbs). Compare that to Mike's street GT3 diff. That's 10 times as much preload!!! I sent out some discs the other day to one of our customers who races a 500whp twin turbo. It's a dedicated track car that's the real deal. He told me that he's been running one of our diffs for 4 years and this is only the 2nd time he's rebuilt it. He said he stacks it to 140ft/lbs when fresh and that given the power they are putting down, that they start to get wheel spin when it gets down to half that, at 70. That's when they rebuild. Just something else to think about when you see posts about how anyone can rebuild their own differential. Sure, you can rebuild it with stock OE parts and get stock performance out of it. Or, you can get it tuned. Every differential out of this facility is stacked to order based on what you tell us about your car and application.

Take care all and have a good evening. I'll check back in the morning to see if more questions have popped up.

MM

 

126 ft/lb in a Cup car and 140 ft/lbs in a TT ... OMG. Now that is super aggressive. Thanks for the useful information Matt. I will think twice before I buy a 997 Cup car

 

Very interesting post. Thanks for the write up.

 

I'm a little confused now. Why would you hesitate to buy a Cup Car?

 

Cup cars are over my pay grade at this juncture. It will be a blast but I like to work on my driving skill slowly... perhaps do the 24 hours of lemon next year lol

What is your ride for track?

 

Matt-

Great informative, no-BS info. Thank you very much.

So, I have a 2010 GT3RS coming in March. Do I just yank the LSD immediately and send it to you? Or is there the slightest chance it will be ok from the factory?

 

hmmmmm ... don't know if Matt has the answer. Someone mentioned the 2010 GT3 uses a zero preload LSD. I don't know if that is true or not. Matt??

 

Bump

 

Hello,
Sorry, I tend to hideout and not post over the weekends. I don't know about the 2010 ones. I'd just be guessing or making something up if I tried to answer, and that's not my style. I'm not much help on 2010.

 

A GT3 is a bit over my pay grade these days. I can't really "run" with most of the members of this forum. Though I should still go in and populate my "garage" just for reference. It's definitely not something I am ashamed of.

My DD is a 2008 WRX sedan. It's slightly modified with some bolt-ons and an ECU flash. Makes about 275chp and is my most powerful car. But it doesn't see much track time because it's just soft and sloppy.

The car I've got the most track miles on is a GC chasss 2.5RS Impreza. I bought it new and beyond the purchase price have about the purchase price once more invested in improving it. It's got a bit of brake and suspension work, but what really makes it go is the motor. I built it myself with high compression pistons, ported heads, Web cams, etc. etc. It makes about 240chp versus the factory stock 165chp. Given it's 2700lb weight it gives STi's and Mitsu Evo's a run for the money on a road course. It's got a short ratio JDM STi 5spd in it, and just needs a couple of our LSD's in it now. It's not very well known but we do Subaru stuff in addition to Porsche.

My other track toy is a 1973 Porsche 914 2.0l. It's got a mildly hot rodded motor in it with the typical Euro P&C's, Web cam, Weber 44's. etc. It's also been regeared with short gears and a GT TBD. But I took it down a couple of months ago for rust repair, restoration and maybe an STI engine swap. I don't expect it to see the light of day for 2 years. It's getting the full monty; GT widebody, bare metal respray,5 bolt conversion, big brakes, roll cage, fire suppression, fuel cell, coilovers, etc. etc. It will be ready to run NASA events when it's done.

I've also got a '74 914 Can Am Limited Edition, called a Bumble Bee as well as a low mile Euro market '68 911T coupe. The Bumble Bee is listed on the Can Am registry. Those are more showy cars than racers. Though I I'm thinking about doing some "Sport Purposes" mods to the '68, mostly just some fiberglass body panels with an ST spec. 2.4L with 5spd. I've got the gearbox and core engine and if by 914 is down for a while I will definitely want something I can at least take to PCA track days and DE's.

With 996 prices plummeting, the wife is hassling me for a 996 C4S. We'll see how sales go through the Spring. The economy has really tightened up business with a lot of racers putting off gearbox work as long as possible. But I suspect she'll get her way. She usually does. She just needs to take a couple more courses here and get some more track time in relatively uncrowded circumstances before she'll be comfortable with a car like that.

Kind of a novel there, and normally I don't go so far OT, but it's your thread and you asked.

 

Wow Matt, I thought I was bad when it comes to car collection. You got some nice project coming in the next couple years with your 914. Impreza can be one fast car especially when you lighten the car and make it more powerful. I am sure you make your track days count when you are at it

996 C4S will be a fun "wife" car especially when you live in the snow country. It's good to start your wife slow when it comes to driving on the track. I just throw my wife in my RS and let her go at it People really treat female driver at the track well because there are so few of opposite gender.

Here is my wife with my RS

 

My wife has her own 2.5RS that's got a few things done to it. It's what she tracks and has done a class with Michael Petiford at GO4IT Racing. She's pretty comfortable on the little private track where she's got half a dozen days. But last month we went out to High Plains Raceway and it was like day 1 all over again. She's really intimidated by cars that are faster than her and doesn't know how to read apexes. If she can trail a good driver and learn the line she does all right but she doesn't know who to "read" a track yet. She mostly needs more time on more tracks with more variety.

As for my "collection"? She made me sell a few cars before she let me bring the '68 home. I had a '66 912, a '76 912E and a '71 914 that I got rid of within 30 days of buying the '68. I've got a bad habit. I don't drink or do drug. I don't gamble or chase women. I just bring home old tired P cars.

 

That's fantastic that you and your wife can do track talk at dinner. I too appreciate the fact that my wife kind of understand why I do the mods to make it go fast. Variety of track experience is the key to build confidence. I am still trying to cut the umbilical cord between wife and I. She will not go on the track without me giving her instruction. She got mad at me the other day when i stop telling her what to do at Infineon ... but she was going too slow to cause any trouble

Now those are some nice "old and tired" P cars. I don't have the patience to nurse a geriatric P car back to health but hats off to you for doing so. alcohol, gambling and drugs are over rated anyway. You can't beat working on your cars and make it fun and fast!

 

With Mikymu's great detailed post I was able to get my differential out in a little over 1 hour. (no wood blocks though, I have a low rise lift). Off it went to Matt who turned it around in 2 days. I went with a 6 plate configuration with a preload of about 90 pounds. The ramps are 50/80.

The fact that he can rebuild the stock diff with greatly improved parts is fantastic. When I put a Guard LSD in my previous 993, I had to have the rack to pinion spacing set by my local shop. They removed the transmission to do that and it cost well over $1k along with the cost of the LSD itself. By rebuilding the stock unit and reusing the factory cage, no spacing changed so I was able to do all the work myself at no cost other than the LSD rebuild. This is one very easy and relatively low cost improvement.