r911

several different types of LSDs

LSD tends to promote understeer on fast sweepers, besides possible on/off nature of the hookup

OP needs to decide what he wants for any of the things that have both benefits & detriments

Amber Gramps

Well all I know is that Marc at Red Line Service sold me the oil he uses and recommended I use GM LSDA (additive) that stinks to high heaven. It's worked flawlessly and unnoticeably for me for a decade now....and it's now got something like 85,000 miles on it.... I guess I wouldn't know if understeer was caused by my tranny or by a prostitute 'cause I've never gotten into a panic situation where it was a problem. ...and believe me, I've pushed it....understeer is the least of my problems. LOLzzz

r911

Don't know Marc at Redline - I am advising the OP based on engineering studies at Lotus and elsewhere

but "if you like your LSD, you can keep your LSD"

unless they are outlawed during the next 4 years

Amber Gramps

Ah, well if he finds code 220 on the option sticker of the car he is interested in then he is likely also a lucky man.

rusnak

Well hold on now, I don't get the attitude about LSD. We can have a good conversation and not get offended.

You would think they'd promote understeer, at least on initial turn in, no? In other words, my observation is that it reduces your ability to turn with the throttle. But you get really fantastic traction on the other hand.

I have PSM, PASM, limited slip rear differential, and also a system that regulates the amount of limited slip through the braking system, on the Cayman S.

I don't understand all that there is to know about it, other than I know it works to keep the car pointed straight ahead. I don't really like the way it asserts itself during a fast corner, but as I said, I must learn how to drive with all of this newfangled stuff on the car. It would be worse with big-*** clown shoe clodgy tires on the car.

rusnak

A limited slip diff will make your car great again.

upshift4

now that is funny!

Amber Gramps

My Tacoma TRD has drive by wire and LSD and traction control so that no matter how hard I slam the gas pedal on ice the tires don't spin and the truck just crawls to a start. Beyond frustrating when in the mud trying to do donuts. You have to push buttons on the dash to override it all.

il pirata

Since the OP is looking for a 911, not sure what specific engineering studies at Lotus you are applying to to use of a LSD in 911.

A LSD will introduce some understeer on deceleration , but the benefits of stabilizing the car under braking outweigh any issues related to understeer. Understeer is easy to tune out. And of course controlling wheel spin on exit is of great benefit.

I do agree that early Porsche LSD preload could be quite intrusive for many drivers, especially the ones set up with 80/80%!

r911

OP asked about a “hot-rod” - he did not say “race car” so I assume he will drive on the street to a large degree

LSD gives you trailing throttle understeer - do you want it? & is it worth the hookup coming out of a corner?

the negatives of any LSD will be very obvious on slick roads, esp. ice but to some extent rain (esp. if the racer boy tires hydroplane)

LSD also makes tight turns in a parking lot harder, esp. if the LSD has high breakaway torque

A Torque biasing( gear type) LSD is usually best for A/X as you don’t care too much about the increased low speed understeer

Asymmetric clutch type is often best for track use

Guard makes both types and can give good advice - the OP should be SURE to tell them it is an old 911 (rear engine, hence high wt. in the rear - even more extreme than a mid-engine Lotus or Boxster, and with no electronic geehoozerie).

Some aspect of an LSD can be offset by suspension & tire tuning

The worst thing a prospective buyer can do is to load up a car with boy-racer bling that uniformed people worship

rusnak

OK, honest question here if I may:

On the Cayman, when I really get on the gas, I can feel the rear wheels spin in both wet and dry. I leave PASM on because frankly I don't know enough about the car just yet, and the Cayman has very different power/ weight/ torque biasing software/ brake biasing/ active dampening, etc etc. I mean, talk about boy racer bling, this car has got it!

So what it does next is what makes me curious - it will oscillate back and forth if you keep your foot on the gas and do not correct with steering input. It's very erie. I am not saying it'll oscillate a whole degree, just barely enough to get your attention, probably like .3 degrees to the left/ right/ left/ right and so on until the car is moving fast enough to re-gain traction. Is that the limited slip diff and software, or is the car using the brakes controlled by an accelerometer or wheel speed sensor? I dare not turn PASM off until I've had time to take the car out to a large open area to understand what it's doing under hard braking and acceleration.

r911

oscillate as in yaw?

il pirata

Call it what you want, a properly setup LSD for the street gives you less wheelspin and greater stability during braking and corner entry than a car with an open differential.

Amber Gramps

https://www.instagram.com/p/BFSRl5Yv...bisimoto&hl=en

^^^ That is my lowly cab with me unaware that Bisi was filming it. I only jerked the wheel to the right because I saw the Bisimoto trailer fast approaching in my peripheral vision. I could have continues that burnout all the way to the rev-limiter. Had I not had at least a 40%/40% LSD one wheel would have spun and I'd have just sat there looking line an idiot going nowhere.

Everything you guys are saying about braking and cornering is correct. I know exactly what my car is going to do....and when I have gotten into a potential understeer situation a quick back-on-the-gas and I'm steering with the rear end again and powering my way out of it. Love it, love it, love it. I think they call that "hot braking" but I don't know.

rusnak

Yes, exactly. It's not like I'm dumping the clutch either, more like roll onto the gas pedal like Walter Rohl on his way to Octoberfest. The rear will not exactly "fishtail" because that implies the action is not controlled. It's very much controlled, but there is enough to make you go "hmm". I would imagine that without limited slip, the car would have spun like a top, but the left/ right action of the rear of the car makes me think that the computer is applying opposite brake and then self-correcting. I'm just holding the steering wheel straight and not trying to correct.