Cannock

I am having some transmission work done right now and while I am in there I was trying to decide if I should add an LSD. I track the car about 8 times a year, the rest of the driving is street. How does the LSD change the handling on the trackand street?

Advice appreciated.

Mark in Baltimore

Shawn,

Do it. On the street, I don't think it makes that much of a difference, but, on the track, it will allow you to put the power down more efficiently in tight corners, especially right handers. Also, it is a boon in trail braking and aids in braking deeper and later. The LSD adds stability when braking due to the lockup ratio. If you can swing it, get the Guards LSD.

Terry Adams

+1
I don't track my car, but the LSD has saved my bacon on a back canyon road. If you have the budget, do it. If not, spend the money first on suspension mods.

Steve Weiner-Rennsport Systems

Shawn:

Good, sound advice from Mark & Terry.

The decision whether to install an LSD really lies with HOW you drive the car and less about where. If you like to drive the corners hard, you will be very pleased with how much more stable the car becomes on braking and corner entry. If you use the car in the manner it was meant to be driven, you'll find the LSD to be a very worthwhile investment.

Land Jet

This is a dumb question probably, but I don't know the answer. On an all wheel drive Porsche, is a LSD necessary?

Cannock

Thanks guys, I appreciate the advice, I was leaning toward getting it but was not sure the benefit if you were not have wheel spin. I did not think about stability under braking and the more of that I have the better .

Martin S.

If I had the budget, I'd get the Guard GT LSD. Besides if Steve Weiner likes it...it has to be good!!!! I have been told, on the typical track, a working LSD is good for 2 seconds a lap....clearly the difference between winning and losing!

mbb993

Very interesting.

I have also always thought of the LSD in terms of its help on surfaces with poor traction. I would like to understand better how it helps over the standard diff under braking conditions and on the track. Perhaps Mark or Steve or anyone else for that matter could explain further? Thanks.

Terry Adams

Here's part of the explanation from an article on the Guard web site

When the rear tires are locked under deceleration, they are forced to rotate at exactly the same rate. This makes the car push the front end. It was now possible, especially with ABS brakes, to get really deep in a corner, brake when the car was turning and not have the rear of the car instantly spin. Try this in an early car and you will immediately see that it is very difficult, if not impossible, to keep the car from spinning. As soon as you begin accelerating, the shafts rotate back and the limited slip became a 20% limited slip. These units worked fairly well in the Turbo style cars, but didn't work perfectly in the RS style cars. They would allow the inside tire to spin on acceleration, in some instances. This was primarily experienced in the higher torque naturally aspirated models and reared its ugly head when the turbo cars had the engines tweaked. The 20% locking percentage was simply too low to keep the tires from spinning, especially when the shafts slammed back on the steep angles from the locked position. In spite of these problems, Porsche knew that they had created something really significant in the differential department, especially when they combined this effect with ABS braking.

Steve Weiner-Rennsport Systems

The real benefit of an LSD in a street/track car is not controlling wheelspin (of course thats an issue with a high-powered car). An LSD's true value is its ability to keep the rear wheels locked together on trailing throttle to stabilize the rear of the car and eliminate the wiggle these all have under hard braking with an open or Torque-sensing differential.

As Martin said, its usually worth 1-2 seconds on a track and a major chunk of peace-of-mind. In extreme cases, it can keep one's shorts cleaner,.....

Martin S.

Go to the Guard Transmission web site Guard Transmission ...on the site you will find an article by Greg Brown, a very bright mechanic and race car prep guy. It will explain the ins and outs of the various iterations of Porsche LSDs. Let's not ask Steve Weiner to re-explain what has already been explained....we need to conserve Steve for other questions.

When you think about it, assuming you drive the car somewhat hard, it really makes sense to have a LSD on a 993 car to work in conjunction with the LSA rear suspension and the ABS brakes.

As an example at California Speedway...coming off the high bank and down the back straight, a 993 car will see from 135 to 140 mph and you need to get the car's speed down to take a 90 degree left turn into the infield track. It is very comforting to know that the LSA suspension, the ABS brakes and the LSD are working together to get you slowed down in a controlled fashion.

Cannock

Thanks again guys for all the info!

ninjabones

Okay guys, I'm looking at a 993 without LSD and would like to eventually make this car more track oriented. How entailed/expensive is upgrading an open differential to LSD?

clubsport1

track the car 8 times a year without an lsd, are you kidding?

Martin S.

expensive. About $2,700 for a Guard LSD, and 5 to 10 hours of labor to install.

The LSD in conjunction with the LSA rear suspension is a sweet combination...cuts down that tail wiggle as Steve said.

All the race cars have them, me want one too...so I had mine rebuilt. I knocked 1.5 seconds off my best time at Laguna Seca this past August. Was it the re-surfaced track, was it the LSD? Who knows.