Now that you guys helped me understand why more clutches results in more lockup, can you share what you've found to be a good setup on track? What ramp angle and what locking factor do you run? What are the positives and negatives (too much entry understeer?)?
Thanks!
That is a VERY open ended question- any sort of remotely educated guess will require a lot of info. Car? Venue? Weight distribution? Suspension setup? What else can/have/will you change? Handling behaviour prior to diff changes?
My immediate reaction upon looking at your car in reader's rides is your proiority should be strength, and whatever LSD setup that nets you can be tuned around with suspension changes after the fact.
I understand, I'm not looking for a particular solution for myself, I'm just curious to observe what works for people and their specific car. I've heard anecdotes about guys having success with anything from an open to a full spool.
For what it's worth, my car is an E30 with a lot of goofy modifications like 335 slick rears, 780whp turbo motor etc. But before all that as an S52 swapped track car, it was hopeless at putting power down out of the slow stuff but that was with an old E28 diff.
EDIT: re: strength, yeah that's why I'm building up a reinforced subframe with a 210mm 2.93 LSD. Not sure how far to go with the clutches though. 2 is trivial, 3 requires simple machining, 4 will require professional outsourcing.
In simulators the setup I like is basically a 1-way LSD with just enough lockup to prevent silly amounts of wheelspin. It acts like an open diff unless you're on the gas which keeps the car agile. But then I usually drive cars that are bigger on grip and downforce than power.
IRL an open diff is all I can afford for now 
but I'd go with a similar setup for my FWD 'rolla.
BigD wrote: For what it's worth, my car is an E30 with a lot of goofy modifications like 335 slick rears, 780whp turbo motor etc. But before all that as an S52 swapped track car, it was hopeless at putting power down out of the slow stuff but that was with an old E28 diff.
It depends much on the specific type of clutch pack diff.
I can tell you that the stock trac-lok in my mustang became an open diff after a few years and most people change the packing order to increase the number of clutches in the pack, but still rebuild frequently.
I went with an Auburn, which worked pretty well, while it survived, which was only 2 years.
Mustang has almost 60% front weight distribution.
That said, 780hp? seriously? Pics and specs please.
For track only, I would think about a spool with that much power.
Thanks guys, please keep 'em coming!
Apexcarver wrote: It depends much on the specific type of clutch pack diff. I can tell you that the stock trac-lok in my mustang became an open diff after a few years and most people change the packing order to increase the number of clutches in the pack, but still rebuild frequently.
Is that just due to the clutches being undersized? Would cooling help prolong their life? I intend to add a diff cooler with a pump.
Apexcarver wrote: That said, 780hp? seriously? Pics and specs please. For track only, I would think about a spool with that much power.
It's actually about 780 to the wheels so more like 900 :)
I've got some pics in my "garage" but this video tells most of the story:
http://www.youtube.com/watch?v=E94HqnpHZjM
BigD wrote: It's actually about 780 to the wheels so more like 900 :) I've got some pics in my "garage" but this video tells most of the story: http://www.youtube.com/watch?v=E94HqnpHZjM
Holy sh1t! 
In all probability cooling would help, however I would need to look to see if its legal for my class (SCCA ESP)
Is the 210mm axle a BMW axle? I am surprised that an axle that size can take your power.
Its really hard to answer your question without knowing the specifics of what components you are talking about. BMW? axle with an OS Gliken or quaife or what? What I mean is that different clutch type designs load the clutches differently and have different surface areas of engagement. Even still, you probably want to talk to the LSD manufacturer and see what they suggest doing.
(Yeah, I know that the quaife isnt a clutch type, just throwing out an example of name of unit)
Regarding the mustang stock piece, I am talking about an alternative packing order of CSCSCSC instead of the stock CSSCSSC where clutch = C and S = Steel for the packing discs.
BTW, please post a thread to the "Build Threads" section. Very interested to hear about your build there
Actually even the 188 "medium case" diffs hold up to 600whp without too much issue. They take more but the ones that fail tend to be due to people doing many wheel-hoppy launches - as air tools have taught us, static load holding doesn't translate to how much inertial hammering things can take. But I haven't heard of a single 210mm unit breaking. These are used on the 1000-1200whp drag cars on slicks and nitrous. My car will never see the strip but I'm doing this for the long haul.
The stock diff is a Salisbury type, with 2 clutches from the factory. The 188mm version will take one extra clutch/plate pair with no changes (there's a spacer inside which you ditch, clearly meant by the factory to leave an option to run 3 clutches for a performance version. Or machine down the case cap to fit 4 (2 extra pairs).
The 210mm version doesn't have room for more, and requires machining - to fit 4 requires machining the inside of the carrier and cutting new oil passages... eww. One option I am looking at that's in the works right now is an unsprung 4 clutch upgrade. This would eliminate the Belleville washers and lose much or all of the preload lockup... which sounds like a good idea for a road racer - no adverse effects on turn in, and more clutches for greater lockup under power.
The stock ramps are 45 degrees and I've been reading that a good upgrade is to machine the power side down to 30.
RE: build, I'm not big on publicizing stuff too much but I do have a build thread where it has gone largely unmolested/unnoticed so that's where I've kept all updates from when I first got the engine build internals:
http://forums.bimmerforums.com/forum/showthread.php?1509062-E30-S52-turbo-track-toy-build
I also have every photo from when I first got the car as an eta in Vancouver here:
https://picasaweb.google.com/111848488207101572298/BimBimRacecarProject
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