So what exactly is the benefit of getting your LSD rebuilt with custom lock up rates? Can someone explain how that works? With a stock LSD for our cas locking at ~25% from what I've read here, how exactly does that affect my rear wheels? And how would that compare to having a diff with let's say a 40% lockup?
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Claus Luthe is my hero.
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Hopefully I can answer correctly...
LSD is inbetween an open and solid diff. Many racers will actually weld their diffs solid so they have an even amount of power going to each wheel. Opposite that, an open diff takes the power coming into the diff and puts it to the one driven wheel while the other just rolls. So in a solid rear end you have two driven wheels, if (for easy round numbers I'm making up 100#) you have 100 # torque coming from the driveshaft, in an open diff one wheel gets 100% or 100# (the driven wheel) and the non-driven wheel gets 0% and just rolls along. A solid diff takes 100# from the dshaft and evenly distributes it to the driven WHEELS and puts 100% or 100# to each wheel (in theory you could put a torque wrench on the input & output flanges and measure this)
So a LSD is somewhere inbetween the open at 0% and the solid at 100%... To do this BMW uses clutch plates inside the diff, they are designed to hold up to a certain load, just as you hear folks saying "my clutch wont hold up to my high HP motor". Say for simplicity the clutch pack inside the diff was designed to hold 25# torque and you have 100# coming into the diff from the dshaft, you would see 100# torque at the driven wheel and since the LSD's clutch holds up to but not more than 25# the non driven wheel would put 25# to the road and slip anything over 25#... giving you 100% at the driven wheel and 25% at the non driven, hence a 25% LSD. Say for example you used two or doubled up two 25# clutch
packs you would have 50# of holding force, if you put 100# into the diff you would see 100# at the driven wheel and 50# to the non-driven, giving you a 50% lockup or 50% LSD.
Diffs are different so to bump up the % lockup sometimes we use one stronger clutch and sometimes we double up the clutch packs. BMW's diffs let us simply add another clutch pack, and with a little machine work we bump up to ~40% - 50%. The benefit is that you put more power to the road so in corners or accelleration you get more power on the pavement...
Hope that helps! -
great explanation! thanks a lot!Claus Luthe is my hero.
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