mrace240sx

I coulda posted this to one of the other threads but felt I might be pulling off topic so here it is.
I keep seeing all these posts about people wanting LSD for their car etc etc. I am a bit confused by this since to me, LSD means that power is distributed to each wheel depending on how much grip the wheel has.
I keep reading that if you have LSD you will make 2 tire burnouts and such which I believe is wrong...

So, my burnouts on my '97 240sx coupe leave 2 tracks. I have jacked up my car and sure enough, the wheels spin in the same direction. Everyone I haved talked to has called this positive-traction, or posi-trac for short. They have told me LSD is where the tires spin in opposite directions which is contrary to what I am reading on this board where everyone seems to want LSD, from what Ive heard posi is much better for off the line.

So why is everyone looking for LSD? I can see if you are doing autocross you may want the added safety and grip for more control, but how in a drag race could LSD be better?
Is my terminology screwed up? My car is the base model with no ABS or LSD and yet my burnouts leave 2 tracks instead of one which everyone Ive talked to has said is much better. Ive been told that the only other late model car with posi-trac is the Dodge Viper... that it is extremely rare to find in a car.

So why is everyone going to LSD?
Please help a confused nissan enthusiast <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

LanceS13

I think you have an lsd.
lsd is positraction...they're one and the same.
The base 240 has an open differential. Open difs spin the wheel with the least resistance to spin. That means if one wheel is spinning and the other has traction, the spinning wheel will just spin faster.
The lsd available for the 240 is a viscous lsd. VLSD's have a fluid that gets thicker with heat. This fluid is between two plates connected to each output shaft. If one wheel starts to spin, it causes friction between the two plates, heating and thickening the fluid. The fluid gets thick enough, it locks the other output shaft to spin at the same, or close to the same, speed. In a turn, the difference in output shaft speed isn't enough to lock them, so handling is maintained. The disadvantage of the vlsd is that the torque transfer doesn't occur until after a wheel starts to slip...but it's better than having no transfer at all. This is cured in clutch type and Torsen difs. There are also locking difs (which I think is what you're calling positraction) that lock both axles together or unlock them with some sort of toggle. If you try to turn with a locked dif, the inside wheel will hop around the corner.
For more info, check out www.howstuffworks.com/differential.htm

(Edited by LanceS13 at 9:40 am on Aug. 29, 2001)

drifterx

LSD does not turn your other tire to spin backwards...
it will transfer more power to the wheel that grips...

Jeff240sx

Posi traction is very very bad to have. &nbsp;If the Viper has it, I would be extremely dissapointed. &nbsp;Unless you drag race. &nbsp;In shop class, my teacher requested that all project cars had a posi differential. &nbsp;This makes both wheels turn at the same time. &nbsp;He wanted posi because we went to the drag strip every weekend. &nbsp;
Anyway, the handling on posi is miserable. &nbsp;In a turn, the outer wheel will hop, because as the inner starts to spin faster, so does the outer. &nbsp;This is the reason that NHRA racers usually have to have their cars towed to the strip. &nbsp;This is like finding an old 3 wheel bike, and welding the 2 wheel shafts together. &nbsp;Sure, it makes cool burnouts, but to turn, you HAVE to get it on 2 wheels.
LSD is a good thing, because it allows you to put more power to the ground and to the car as you come out of a turn. &nbsp;
-Jeff

LanceS13

no...positraction is not a locked dif...at least not techhnically anyway. &nbsp;Posi is good to have...it's the same as lsd. &nbsp;A locked dif is very bad to have in terms of handling. &nbsp;I'm sure the Viper, being mainly a road course car, has a limited slip/posi--most likely a Torsen type.
And you got it backwards Jeff. &nbsp;With a locked dif, the inside tire will hop b/c it's trying to spin faster to keep up with the outside tire.

so in general, would everyone agree and an LSD is more for racing (not drag-racing) and probably wouldn't be the greatest thing for the street. &nbsp;I'm about to drop $$$ to install one, and I need to know if I'm making a mistake. &nbsp;I don't wanna round a corner and suddenly lose all traction....

LanceS13

No.
An lsd is actually safer b/c your less likely to loose traction. &nbsp;You don't want a locking dif on a street car or even a road course car...that's for drag cars only. &nbsp;There's a difference between lsd and locking dif. &nbsp;If lsd's weren't safe, no cars would come with them from the factory. &nbsp;If you want to learn more, check out the link I posted a few posts up.

Jeff240sx

Ok. &nbsp;I was under the impression that posi was locked. &nbsp;Anyway, in shop, we had locked differentials then. &nbsp;We took them around the parking lot a couple times, and shredded a set of rear tires in doing so.
-Jeff

so will an lsd cause both wheels to spin at the same speed around a turn, and therefore cause the inside wheel to hop?

LanceS13

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from vancouverS14 on 3:10 pm on Aug. 29, 2001
so will an lsd cause both wheels to spin at the same speed around a turn, and therefore cause the inside wheel to hop?</td></tr></table><span id='postcolor'>
NO!
that's why it's called LIMITED slip. &nbsp;It will slip when it needs to...like when turning. &nbsp;But it will &quot;lock&quot; when one wheel starts spinning significantly faster than the other(like in a one-wheel burnout). &nbsp;The difference in the speeds of rotation of the two output shafts isn't enough to thicken the viscous fluid to &quot;lock&quot; the dif when you're simply turning a corner...not enough friction between the plates.