This was too good to let die on the locked up thread

Now, lets talk about reality and the LSD. nothing to do with Carls stuff, good, bad or indifferent. Effects of an LSD on the track

Greg brown said,

"Mark:

In a 911 based vehicle, the difference between a limited slip from an early "cup" car and a current "cup" is worth 3-5 seconds a lap, depending on what track one is on. The difference between a "1975" design limited slip and an early "cup" car limited slip is just as big a difference.

What makes you think that the same would not apply to a 928? "

So, anderson who ran a 1:30.xx at laguna seca, would have run 1:25 with a "different " LSD??

I think you are falling in to the "modification gain" pit.

I can tell you this Greg, having driven the same exact car with and without the LSD. (vs open diff), there was a subtle difference. probably about a second if you really drove the non LSD carefully and it certainly depends on the track
If you are going into a turn, trail braking and the car is not locking up , getting oversteer and exiting early with full power, the LSD is working. not much you can do to increase the performance there. I would say, most have too much lock up and lose a lot of ground (and rubber) coming out of tight turns with a tighter wound up LSD than our stock LSDs. after alll , didnt anderson run a stock GTS box for many many years????

Mk

 

The difference between you and a pro driver is the ability to discern subtle LSD behaviour.

Sometimes I do mods to diff lockup ramps for real actual pro drivers and they find real improvements there. Mostly in decelleration lockup and how the car behaves entering a turn.
The idea of an LSD being only slightly better than open is silly unless you're not very in tune to your car. I know that I'm not at the level to be able to use small differences in diff lockup.

I do know that having weak decelleration lockup will suit most amateurs just fine because it will prevent scary things from happening like push and then immediate oversteer but that leaves alot of potential for control and lap times on the table.
Understanding how your car is going to behave under decelleration going into a turn with various setups is really important but not widely understood. Fanboi-ism beating of drums isn't going to help you get any faster.

All of the wonderful intricacies of LSD diffs are lost to drag racing straight line masses. Like in Carl's thread where customers like the LSD brand when they only drive their cars in straight lines. It's meaningless and to look to them when considering Porsches and road racing is wasted time.

 

Mike - remember, mark drive a car for quite a while without even feeling that the clutch pedal arm was nearly falling off. He DOES NOT SEE/feel DETAIL.

He only sees grand, sweeping generalizations based upon his own world view.

 

Coming out of a corner with a worn out LSD on my GT3 I lost a lot of ground to a guy driving an identical car with a GT gears LSD. Same car, tires etc. He pulled away like he had a turbo! Can a 928 be so different?

 

Two legs are better than one. ..

 

I think that depends on which 928 ...

 

I think it is also fairly important to remember that you are going to need to be making changes to several other components when you have a LSD installed, to really be able to take advantage of what benefits it will give to you.

I wish that there was some magic part that would instantly take off 10 seconds on your lap times, the second that you install it, but the reality is that simply does not exist. Setting up a car is a very tricky business, and for those who are really good at it, can indeed help a driver through proper setup of the whole car, shave some seconds off, by also including a LSD in the setup.

One of the things to remember here though, is that depending on the construction of the differential, as well as condition and durability, you can have very different results from weekend to weekend. Some differentials work wonderfully for a short time and require quite a bit of maintaining to keep them in their top form and operational state, others require less maintaining, and will give a more consistant week after week performance advantage. Regardless of this, however, it is the complete setup that really makes a car fast, and not any one part. When you get into a car that is set up correctly you feel more comfortable pushing the limits, and as a result your lap times are better.

I guess my point here is that Yes there is most certainly an advantage to be had in running a LSD in the 928. How much of an advantage is going to depend greatly on whether the car is correctly setup to take advantage of the addition of the LSD.

Erik Johnson

 

Mark:

I would not expect you to need/be able to tell a limited slip from a non-limited slip, much less a 'high tech" limited slip versus a stock limited slip. (Nor, is Mark Anderson a good gauge of this.) I agree that a high-tech limited slip would probably not result in significantly reduced lap times, for you.

You (by your own words) concentrate on being super smooth and super "easy" on your equipment. I think of you as the ultimate "Malibu Grand Prix" driver....don't scrub any speed off and keep the cornering forces very equal and smooth.

Mark Anderson tends to be "insensitive" to anything. He just drives whatever is in front of him.....whatever the condition....and does so, pretty quickly. The guy would be frightening with a really good car, with a really good set-up, and really good tires....all of which he never has.

The "new" generation limited slips benefit drivers that get into corners very, very deep and use a tremendous amount of "not very smooth" trail braking. The increased locking percentages, under de-acceleration, helps keep the rear tires "driving" at the same rate....which reduces "turning induced oversteer". Vehicles equipped with "leading edge" ABS systems can really benefit from the current generation of limited slips.

The driving techniques required to turn very fast laps with the current generation of Cup Cars would be "revolting" to you. These cars, since they don't have ABS, require really "radical" driving techniques to keep the rear tires from locking up and the rear of the car going straight. Very few, if any, Cup Car drivers, in the events that you participate in, are going to be using these techniques.

The guys that are "uber" fast, in these cars, certainly are.....and they "depend" greatly on these "newer generation" limited slips.

 

I'm very glad to see this subject re-opened, I know I have a lot to learn about this stuff and unless you guys are talking about it, I won't get it. Please keep it up and Greg, get GT-gears in here also. His input has been the most valuable thus far.

 

Great thread....glad its restarted...................... Clearly a newer design is going to benefit a race 928 just like any other proper mod, say better brakes or suspension.....its all about tuning EVERYTHING together to suit the driver AND the track...... 997 Cups and their support crews are VERY good at dialing in every little thing to suit the driver.....and we all know that having a car that just feels "right" (I like to call it "in the zone") makes all the difference!! Being absolutely confident in the car and what it will do at the limit is HUGE....that alone is probably 1-2 seconds a lap

Here is my example from the SAME day.... LSD is working, even though I am still stuck in only 4th gear

Here is literally the next session when the sway bar broke causing the LSD to slip

The difference........9 seconds per lap........................in the 1st video I was running 2:06's with the dead LSD 2:15......... I just couldn't get off the corners....with my brute 257ftlbs of torque..... Whats really sad is I raised the front suspension 10mm just before the LSD died, since it was bottoming really hard in T8 at over 100mph....the car felt GREAT...much more controlled....then BAMM...it sucked.....just like that.....

I'm gonna start saving my $$$$ right now for a Guard-Brown LSD......I'd love the carbon clutch too....but the LSD is probably a better idea

 

Greg brown said,

"Mark:

In a 911 based vehicle, the difference between a limited slip from an early "cup" car and a current "cup" is worth 3-5 seconds a lap, depending on what track one is on. The difference between a "1975" design limited slip and an early "cup" car limited slip is just as big a difference.

What makes you think that the same would not apply to a 928?





I would agree with the above, the faster the car the more it will be hobbled by an ineffienct LSD. An electronic diff will be much better again.

 

By 'electronic', do you mean PSD? My recollection is that neither Greg Brown nor Mark Anderson are fans of the PSD for track use. Something about the PSD essentially being an open diff on deceleration?

 

Yes and no, I am not referring to the PSD however there is many electronic differentials out in the street and racing world these days. They can have any type of programming the designer desires and race cars can tweak their handling by adjusting the clamping force applied to the clutch packs. The best LSD will never match an equivalent electronic differential.

 

The PSD is not an open diff on deceleration! it works both during acceleration and to counteract the Ferraria effect during deceleration. Please watch the promotional video on YouTube. It is all explained in there.

I also race a car with PSD and I find it much better than my other track car, which has a viscous based LSD. Contrary to popular belief, the PSD is a great system, even for racing at our level of competence.

The fact that Ferrari, Porsche and BMW are all fitting a modernised version to their cars speaks volumes...

 

To be clear I was trying to use the psd without the computer by using an adjustment screw instead of the slave.