What to expect from LSD on the street

[afterburn 549]

Ok, consider my next mod. If my car is tracked little ..will a LSD ruin it for the street ?? ( I do mean a 60 /40 not a torq bias thing
Or and what will I expect to feel / see in this situation.............

[equality72521]

LSD will make it hard to concentrate. You may feel you can fly which can be very dangerous. Oh, wait. You're talking about for your tranny aren't you?

[ZOA NOM]

I have both. My daily driver has no LSD, and my track car has it. The difference I notice is during trailing throttle, I get less oversteer with it.

[afterburn 549]

Right now I have almost no traction when I stand on it..just brakes loose, so maybe a LSD is the next thing...unsure,, as I do not want to make 1 to 2 G mistake............

[spuggy]

Originally Posted by afterburn 549

Right now I have almost no traction when I stand on it..just brakes loose, so maybe a LSD is the next thing...unsure,, as I do not want to make 1 to 2 G mistake............

A LSD will only make a tiny amount of difference to straight-line traction, so you should maybe think about addressing that problem. Bigger tires, stickier rubber, driving more gently when the road is a skating rink, that kind of thing

What the LSD will mostly do for straight-line traction is make it much more controllable when you break it.

With an open diff, over-estimating available traction - or simply too much throttle, too fast for conditions - spins one wheel, takes you 30 degrees off-track and can put you in the next lane before you can react.

With an LSD, the same thing will spin both rear wheels, the car wags it's tail slightly, and a slight track adjustment - like 1" or so on the steering wheel - (and feather the throttle and/or shift, obviously) is all that's necessary. Much more controllable.

With an open diff, overrun up to corners, the back feels a little "loose". The feeling persists through the corner.

With a plate-type LSD, decelerating for corners, the rear of the car is planted. It just squats there. And feels much the same as you start to drive through the corner.

Because the rear of the car is being kept straight by the locked-up diff, it resists turning in initially - there's a momentary delay, maybe 1/10 of a second - before it "catches up" with the control input. It feels odd at first, you really notice the extra "push". But it's predictable and consistant (if the diff is set up right) and you adjust readily. Like maybe a week, if driving the car every day. It's not noticable on all corners.

Sometimes you can feel and hear the LSD unloading one set of ramps and loading up on the other set - like when you reverse out of your parking spot. Clanks a little. No biggie.

I got a 40/65 diff - it locks up 40% on acceleration and 65% on deceleration (due to the angle of the slope of the ramps the plates slide in). I think the shim stack is adjusted to break free @ about 60-70 ft/lbs, but I forget exactly.

My tranny guy advised me that 80% diffs were really for rally stages on loose surfaces, or dedicated track cars.

The factory "40%" LSD's were 29-58 ft/lbs before 1984, but the post-84 LSDs are the so-called "snow-only" LSDs which slip @ 7-25 ft/lbs (and it's a struggle to get 25) - but still rated "40%"..

Good information here:

http://www.guardtransmission.com/velocity.htm

Frere says in "Porsche 911 Story", p183, Chapter 7 "The 911 in motoring sport" (sic):

"In some races, following the lead set by the turbocharged Type 917's, the Turbo-Carerra was run with solid drive to the driving wheels instead of the more usual limited slip differential with an 80 percent locking factor. In practise it does not make much difference to the handling and it certainly allows the driver to use a lot of power coming out of the corners. In this context, it should be remembered that tests carried out at the Weissach circular pad with a Type 917 racing car in 1969, using differentials with various locking factors, had indicated that the best results were obtained with the highest locking factor which made the car behave more consistantly under varying throttle positions. This is probably due to the fact that the higher the locking factor and the pre-loading, the higher the tendancy for the car to proceed in a straight line and the less likely it is to oversteer on the overrun."

I'm much, much happier with the 40/65 LSD than I expected to be, to the point where I think it's the best money I spent on my motor/tranny rebuild.

I put one in because I thought there would be some benefit, and because I was rebuilding the box anyway. I never expected the difference in handling to be so pronounced.

It's noticable (at least to me) on the approach to every corner, and going around every corner. You may not notice it on acceleration, but the chances are good that if you do, you'll be pleased it's in there doing it's job...

[dvkk]

Originally Posted by spuggy

A LSD will only make a tiny amount of difference to straight-line traction, so you should maybe think about addressing that problem. Bigger tires, stickier rubber, driving more gently when the road is a skating rink, that kind of thing ...

That's not what my car is like, mit ZF. I found straight line traction was amazing. One friend commented after a full throttle rip through a couple of gears that if it was his car he would have spun out almost immediately.

With an open diff, as soon as you lose traction with one tire, you have almost no acceleration. With a ZF, as one tire may want to lose traction, the other tire drives the car.

YRMV.

[dd74]

Will a 911's handling characteristics improve with LSD no matter what its weight and horsepower? I've been told that because of my car's weight and horsepower, LSD is not entirely necessary for track duty.

[gestalt1]

i've studied different differential quite a bit on this board. an LSD helps under braking/trail braking into a corner but does induce understeer through the corner. most say a swaybar adjustment will counteract the understeer. my question is what swaybar adjustment is theo be made to correct this understeer?

also, has anyone tried to drive on the street with a locked diff? i'm sure this would not be very good for CV joints but welding the open diff sure is cheap!
-matt

[911teo]

You need to stiffen the rear sway bar to reduce understeer. If u maxed out then loosen the front sway bar. If maxed out that hopefully you have adj shocks...

Welding the open diff is not a good idea... besically your car will not go around the corners very well....

[911teo]

Originally Posted by dd74

Will a 911's handling characteristics improve with LSD no matter what its weight and horsepower? I've been told that because of my car's weight and horsepower, LSD is not entirely necessary for track duty.

I agree with this statement. For lighter cars with less power the LSD (whilst always a nice thing to have) does not bring such an advantage.

[boba]

Originally Posted by gestalt1

also, has anyone tried to drive on the street with a locked diff? i'm sure this would not be very good for CV joints but welding the open diff sure is cheap!
-matt

I drove an ex-Firehawk 944 on the street for a number of years. It had a motorsports LSD and was as far as you would want on the street (lf you were rather hard core, my wife loved it). You would chirp the tires on tight corners and get very strange looks at the supermarket parking lot pulling in or out of a parking space.

We have welded open diffs for the track and it is a track only setup. You have to be able to set up the rest of the suspension for this mod. It would not be fun to drive on the street.

[Grady Clay]

“What to expect from LSD on the street”

Addition to most of the above:
Greater rear tire wear.
Slight change toward ‘push’
Noisy as the tires scuff on tight turns while accelerating, particularly if there is any sand, etc. on the pavement (like turning into a drive).

Best,
Grady

[afterburn 549]

hmm... sounds like the right direction to me so far..as getting the pwr to the ground in my ego machine is disconcerting as I have to let of the the gas repeatedly to get traction.

[GrantG]

LSD is a big improvement on street as well as track - just adjust swaybars slightly (if yours are adjustable) to compensate for the additional understeer caused by the LSD.

[John P (w/a T)]

My '71 has a factory LSD (pretty mild). Where I really notice a difference is in getting the power down and accelerating out of corners.

Me likeeeee.

My 1.5 cents.

John

[Steve@Rennsport]

Originally Posted by dd74

Will a 911's handling characteristics improve with LSD no matter what its weight and horsepower? I've been told that because of my car's weight and horsepower, LSD is not entirely necessary for track duty.

Just another opinion,...

Adding a clutch-type LSD makes a big difference in handling and stability and for me, there are no downsides other than cost.

For cars with a lot of power such as 3.6-powered 911's, its a necessity!

For any track use, its a no-brainer.

[Porsche virgin]

Originally Posted by dd74

Will a 911's handling characteristics improve with LSD no matter what its weight and horsepower? I've been told that because of my car's weight and horsepower, LSD is not entirely necessary for track duty.

This may not be totally applicable, but I've had two Miatas (low hp, low weight), one with a Torsen LSD and one with an open diff. The difference in tight turns was huge. When I would give the car with an open diff. gas, even with R-compound tires, the back end would start to slide (which is fun, but not fast). The Torsen-equipped car stayed planted.

I can't speak to the more expensive plate-type or spool-type diff.

[dd74]

Originally Posted by Steve @ Rennsport Systems

Just another opinion,...

Adding a clutch-type LSD makes a big difference in handling and stability and for me, there are no downsides other than cost.

For cars with a lot of power such as 3.6-powered 911's, its a necessity!

For any track use, its a no-brainer.

I like your opinion more, Steve. PM'd you, BTW.

[dd74]

Originally Posted by Porsche virgin

This may not be totally applicable, but I've had two Miatas (low hp, low weight), one with a Torsen LSD and one with an open diff. The difference in tight turns was huge. When I would give the car with an open diff. gas, even with R-compound tires, the back end would start to slide (which is fun, but not fast). The Torsen-equipped car stayed planted.

I can't speak to the more expensive plate-type or spool-type diff.

Ah! That's exactly the example I've been looking for. On tight tracks, my back in slides out as well. I've nearly twice the hp. of a Miata though I assume a couple hundred pounds heavier. Thanks P. Virgin.

[911boost]

Also expect to hear a wierd sound when you back up and turn.