I'm wondering if an LSD upgrade will be worth while, like on the 996/7 GT3s? Does guard offer one?

I'm under the impression that the GT4 has a more traditional lsd and not the ediff in the 991 GT3.

 

https://rennlist.com/forums/gt4/8959...l#post12746584

Post #139

 

I, too, have been surprised by the lack of interest expressed on this forum for an upgraded LSD. I've had a Guard LSD in my last 3 Caymans. The GT4 has PTV and perhaps people believe a better LSD is unnecessary. Does anyone know how PTV will operate with a different LSD?

 

I chalk the current lack of interest more to there being still relatively few cars in people's hands, and even among owners, many probably still have not been to the track much, and those who have been are probably focused more on learning the car and maybe dialing in alignment and sway bar settings than deciding what aftermarket parts to install. And then of course we're headed into winter, except for the Aussies and Kiwis on here.

But if memory serves, I believe I remember reading that the GT4 uses the same diff as the 981S, for which Guard offers rebuilt internals and full replacement diffs, so I can't imagine why they wouldn't work on the GT4. (EDIT: No they don't offer 981 rebuilds, sorry!)

 

PTV is more a new name than anything else. It's pretty similar to what they were doing previously with traction control through ABS actuation on top of a very anemic mechanical LSD. I would have to double check but I think they are still using the 22/27 lock up LSD that was on the 987 cars.

We do have an LSD for the cars with the oil pump. We did a small number of prototypes and put them in cars earlier this year. When our current production of 987 LSDs is done, it will include a batch of 981 LSDs with oil pump drive gears.

And a word to the wise. I have been told that Giken hasn't actually made a new LSD for the pump drive gearboxes and has just been taking their finished units and machining them down to allow the oil pump gear to press on. Given that their LSDs already have a propensity to break off right at the bearing flange, I would be scared of any unit that was machined after heat treat to fit the drive gear. This is what I am talking about:

 

We do NOT offer internals for the stock LSDs. There's just too much that needs to be replaced to make it cost effective.

Yes, 981S and GT4 LSDs are the same. Sorry I didn't state that more clearly in the post above.

 

Whoops, sorry about that. Edited my post.

 

No worries. There's a really old thred on Planet9 where we dissected the LSD and openly discussed making parts for it. I'm pretty sure late in the thread I posted that we were not going to service them, but a lot of times guys find the thread on a search, read the first little bit of it and then send me an email asking me to rebuild their LSD.

If it weren't for the value to people of being able to see inside the stock Cayman LSDs and just how bad they are I would go completely kill the thread to stop the confusion.

 

I would guess that if one used a high locking factor for over-run/braking, that it might reduce the effectiveness of the PTV (which relies on braking the inside rear wheel on corner entry to adjust yaw and reduce understeer). Lots of LSD locking will cause the outside rear wheel to also receive this braking (think of a completely locked rear axle for illustration), nullifying its efforts to improve turn-in.

This could probably be corrected through suspension tuning, but the PTV function would be burning the rear brakes with no benefit (might be better to disable this function with a hardcore LSD - probably requires a hack of the ECU?).

Or maybe this isn't a real issue until locking factors approach a true spool rear end?

 

We need a better LSD so less "ptv" needed?
I think a guard is adjustable (on track with Orbit) as we messed with one at Sebring at one time. Matt?

 

Hello Peter,

You are correct, the LSD is intended to make the PTV less intrusive.

Grant,

The place where the PTV is a problem is on throttle. They are using the ABS to compensate for wheelspin when you get on it. Obviously, braking while you are trying to accelerate your vehicle is going to ultimately slow it down. It also is the source of hot cooked calipers and high rear brake wear that so many people complain about on these cars. When the LSD steps in upstream of the brakes, it makes you exit the corner more quickly and you don't toast the brakes.

We don't use particularly high locking factors on Cayman LSDs. Usually in the 45-50% range. It has a bit better traction and stability in general than the rear engine cars. We've played around with a lot fo different options over the last ten year since the Caymans were released and feel like we've gotten it pretty dialed at this point. PTV doesn't really change that. We've been dealing with ABD, PASM, TC and PTV for as long as Porsche has been throwing letters at their particular versions of traction control.

 

Matt, thanks for all the information. Very helpful. I'm wondering if anyone has already found a way to turn off PTV in the 981. With a proper LSD and a proper track alignment, I think PTV would be an undesirable feature.

 

thx

 

Can PTV be disabled just by turning off all traction/stability control?

edit: seems like no.

 

Matt,
I have had your LSD in my 2010 CS since the car was new. Led to take that action due to the
LSD weaknesses of the 997.1 GT3. Any chance of a group buy on LSDs for the GT4?
CB