What's the difference between LSD and Posi differential?
 

How much improvement would different gearing help in the 1/4 miles? I know it's a compromise that I would have lower my top speed to get improvement in the 1/4 mile ET. But how much improvement are we talking about?

Posi-traction was a brand name for particular type of limited slip differential back in the day. Now a lot of people refer to any kind of LSD as "posi."

I thought LSd was thought of as how we have it in the I30t where it grabs when the other wheel is not etc like cornering. And I though "posi" was generally thought of as basicly both wheels spin together at all times. I know this was the setup with my old Delta and thought the term was kind of a divider for those two setups?

SuDZ

No, both wheels spinning together at all times is a closed differential, and is pretty much only used for serious off-road vehicles because it makes turning suck and kills your tires. The other end of the spectrum is open differentials, which most cars have. Then there's LSDs, which come in many types: viscous, torsen, clutch, etc. Different implementations for essentially the same result.
As always, I suggest to anyone who's interested to read HowStuffWorks: Differentials.

A differential that turns both wheels at the same speed all the time is called a "locker", pretty much only used in drag racing.

A torsen, or helical differential such as the Quaife or the 2k2 optional diffy are not technically LSDs. LSDs are limited slip, in other words..they sense slip and then have a delay while either clutches engage or disengage or while there is a fluid transfer. The formentioned torsen and helical (quaife and 2k2 max) differentals are ATB (Automatic Torque Biasing) differentials. They have no delay time at all and are constantly changing torque sent to each wheel. The ATB differentials are infintely variable in how much torque they can give to each wheel while LSDs are not.

As for the gearing of our cars...I don't think you'd see much gain by changing the final drive. Mabye a little on an AUTO...but not on a 5-speed.

Here's some CarTest2000 sims.

Stock 95 GXE Automagic

w/OE 3.62 gears, w/hypothetical 4.10 gears
0-60: 7.62, 7.22
1/4 mile: 15.85 @ 88.8, 15.69 @ 90.5
Redline in 3rd: 128, 112
Redline in 4th: 187, 164
60 mph in 4th: 2150rpm, 2450rpm
70 mph roll-on to 0.5 mile: 18.95 @ 113.06, 18.81 @ 112.31
70 mph roll-on to 1.0 mile: 34.07 @ 123.9, 33.78 @ 126.40
70 mph roll-on to 1.5 mile: 48.22 @ 129.9, 47.65 @ 132.44
Top Speed: 136, 137

=============

The hypothetical 4.10 gears look pretty darn good to me! :)

3rd gear is shortened to the point where you're no longer bogging through the last few hundred feet of the 1/4 mile and you can actually get some decent pull. Gains of almost 0.2s/2mph. The other big thing is that even though redline in 3rd is cut back all the way to 112 mph, 4th gear is now shortened enough that it would probably actually pull not unlike 5th gear does in the 5spd's. From the 70 mph roll-on tests at longer distances, 4th gear, even with the 4.10's, keeps pulling pretty good. So instead of only 3 useful gears with the OE 3.62's, the hypothetical 4.10 gears would allow all 4 gears to be useful.

Not a bad mod (even if it's only hypothetical) if you ask me :)

Re: What's the difference between LSD and Posi differential?
 

You know you want an LSD like mine :D

It would be a nice mod, if I had the bolt pattern diameter of the auto diff. I could check it vs my se-r diff with the 4.17 gear. Imagine a 3400-3500rpm stall convertor, 4.17 gears, slicks and n2o + boost. Can you say consistant 12 sec car on almost any given day :eek:.

So with a LSD it would improve performance overall, not just at the launch?

Well, once you get traction the LSD is of no benefit in a straight line. But before I got the diff, I could break the tires loose from like 20mph, not anymore. And the cornering is amazing.