How important is LSD?

[Don Plumley]

In my track car search, LSD is not a common find.

So how important is LSD for DE/TT? A GT unit is $2150 plus install...

Just wondering in the list of priorities where this fits in.

Thanks!

Don

[earlyapex]

I have a Guard ZF unit in my track car and it makes a very big difference in how it handles. I really love it. That said, it was expensive and it should not be a priority in you purchase. There are plenty of very nice cars and fast drivers who don't have LSD's.

[juanbenae]

very important if you go to one of these shows>>How about a Dead head?

[nostatic]

mine has factory, so I have no reference without it...

I believe Tyson was saying it depends on the track...on some it is a big advantage.

[Mahler9th]

You have to decide whether you want a race car or a "track" car. There is a difference. I suspect that the preponderance of the people who respond to these posts are street and track day drivers. Some would call them racing wanabees-- I would not. Just recognize that there is a difference. For a race car, you need some sort of lsd and if the car is correctly prepped it will have one. If it doesn't have one, it is not (a finished) race car. I know of some well-prepped 911 race cars for sale here in NorCal, some are not advertised. Even iff you buy a track car with some bhp and some decent sized tires, you will be adding an lsd pretty quickly.

- Mike (mahler9th@aol.com)

[Don Plumley]

Thanks Mike - this thread covers the path I'm on. In short, I'm buying/building a C2 based DE/TT car. The purpose is to build seat time and driver skill, not race. I'll drive it to/from the track.

The reason for my question is the first couple of candidates (street carts) that I'll convert to a light track car do not have LSD. I'm told that in C2 coupes, LSD is a rare option, so holding out for LSD might take a long time.

Please let me know if you hear of a good candidate!

Thanks,

Don

[Mahler9th]

If you are driving to and from the track, you have to decide what comfort items you are willing to forego. I drove my current car to and from the track for two events and it was fine, but I needed a support vehicle for all of my "stuff." Hank Watts drove his car to the track for a while... If you are trying to optimize your spend, then a lighter car makes more sense. There is a HUGE difference in the maintenance/repair costs and wear and tear costs when you compare 964 cars to earlier cars. Be aware of that!!!

I think a 964 is a bad platform from a financial perspective unless you are willing to take a big loss after 2-4 years. It is too heavy and there are too many issues. However if creature comfort is what is important, then it is a better choice.

Because of the bhp/tire of the 946 you will wind up with lsd pretty quickly. Be aware that you can run ANY G50-type lsd in a 964, including some of the exotic racing diffs. And they are not necessarily more expensive than the stock street car units. So there a are lot of cool choices. Rely on advice from Hayden or Paul Guard or somebody that knows racing!!!

I do know of some 964s around here. I think you should contact Ken Shahoian who has several of them and has a lot of experience. He knows a lot about all of the cars and will likely have a great perspective that is relavant if you continue down the 964 path. And he has ways of finding cars that are STEALS!!!!! Who knows, he may even have one for sale.

Give me a call and we can talk and I can put you in touch with Ken. (510) 713-9248

- Mike
Mahler9th@aol.com

[Bill Verburg]

Greg Brown wrote one of the best pieces on lsd I have ever seen in the feb '01 issue of Velocity the organ for th Porsche owners club, I hate to post stuff like this w/o permission but giving credit and for educational purposes I hope no one minds

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[earlyapex]

Mike, I wish I knew you before I bought my stock 78 SC and converted it to a track car.

FWIW I had 6 days at Laguna Seca with an open diff. and then the transmission was rebuilt with a 40% symmetrical Guard ZF LSD. Whereas the car used to wiggle its rear end under hard braking i.e. T2 the car now was very stable under braking. It was expensive as are all things done the first time, but I am very happy with the results. I got my LSD from Steve Weiner at RennSport Systems.

As you've already stated, finding a car with a LSD in good condition is tough. You are better off looking for a car that is in good condition and has all the safety items that will be needed for track use. This is assuming the car has the prerequisite brake, alignment, suspension, etc. work to make fun and safe to drive on the race track. When you start worrying about your lap times or race finishes, get a LSD.

[Don Plumley]

Great! Thanks Bill.

Don

[Don Plumley]

So I quickly read this article and for Carrera's and C2's, it says:

...They have limited benefits on the race course, because they release at very low torque numbers. If you have one, lose it for one of the better later limited slips that I'm going to discuss and your lap times will improve instantly.

Their bottom line was to get the right LSD, or don't bother. This correlates with what earlyapex posted, and what sounds like solid advice:

Originally posted by earlyapex
As you've already stated, finding a car with a LSD in good condition is tough. You are better off looking for a car that is in good condition and has all the safety items that will be needed for track use. This is assuming the car has the prerequisite brake, alignment, suspension, etc. work to make fun and safe to drive on the race track. When you start worrying about your lap times or race finishes, get a LSD.

When you start worrying about your lap times or race finishes, get a LSD. Corollary: The right LSD, not the factory one.

This board rocks - thanks for all the support guys!

Don

[Ho Hum 74]

Couple of things:

1. LSD is essential for any RACE car. My RS America (without LSD) had slippage coming out of some corners. Hence why I sold it and am looking for a C2 / C4 just like you. C4 has a LSD.

2. I put a LSD 80% lockup in my 1974 911 race car and the biggest change outside of no more wheelspin was the incredible control and stability I now have under braking. You can really trail brake it very deep without the rear end coming around. The difference is simply amazing .

3. Only detrimental effect was more understeer under power exiting turns. But with more trail braking and hence rotation this is quickly taken care of.

4.

I think a 964 is a bad platform from a financial perspective unless you are willing to take a big loss after 2-4 years. It is too heavy and there are too many issues.

I have to say that I completely disagree with this statement. Not only is it misleading but it's not factual. The 964 is a VERY competitive car in E and lightened it can be competitive in D. Sure there are the 964 cups in D which are better but there aren't a proliferation of these. The 964 is a wonderful car to drive, retains that 911 feel that we all love so much and is very quick on the track in the right hands. To give you an example: My stock 93 RS America did a 2:45 at Road America on STREET tires and Pagid Orange brake pads. That would have qualified me in 28th position out of 68 cars for this year's club race with a street car. My 1974 Euro Carrera does 2:42 and is fully race prepped so I can tell you that the 964 is very fast. Chip Smith did a 2:37 at Road America in his E class 964 and came second in the sprint to a very well driven and prepared 944T.

As for expense, no Porsche is cheap but a well looked after 964 is a quality car and handles the abuse of the track very well. You can do your own valve adjustments if you are mechanically inclined as it is not a black art. I would say that in retrospect I have put more $$ into my 74 race car than I would have into a 964 and would have had greater reliability. I'm looking for one as well.

Buy yourself a 964, don't let anyone scare you off. They are powerful, have incredible brakes and are a pleasure to track. Enjoy!

Tristan

[J P Stein]

Bill:
I guess it should come of no surprise that some folks would
disagree with your Mr. Brown. Mark Donahue was a huge fan of the locked differential and, to read the article, folks shouldn't even bother to make a Torque Basing differentials.

2 men claiming to be Jesus....one of them is lying.....how do you tell.....go with the one that performs the best miracles.

[Tyson Schmidt]

I also noticed that he doesn't quite grasp the concept of pre-load.

Pre-load only determines how the diff acts under "maintenance throttle". In other words, neither accelerating nor accelerating. Once you hit the throttle, or fully lift throttle, the pre-load is irrelevant, since the concave spring that provides the pre-load is fully compressed under these circumstances.

The friction disc orientation, and number of friction surfaces is what determines the percent of lock-up. Pre-load only determines the "minimum" lock-up, not the maximum.


Otherwise, an excellent article.

[KTL]

In my limited experience, i've found that used/not rebuilt LSD's are a total ripoff. The price people ask for their used, most likely worn-out, LSD units are silly. The factory friction discs have a limited lifespan. So buying a used one will most likely result in obtaining one that is tired. Especially if you were to get one from a 993.

If you decide to get a LSD Don, give Paul @ Guard Transmission a call. Last year he told me he offers rebuilt street car LSDs for 1,100, and rebuilt VERY low mileage Porsche Motorsports LSDs for 1,350 He typically has a supply of these Motorsports units from new GT3R owners who opt to change their LSD immediately to a Guard Chromoly unit.

I was told the standard friction discs in the street car LSDs are absolute trash which wear out almost immediately. These MUST be exchanged for good quality plasma-sprayed friction discs to enjoy proper limited-slip action, and that's what Paul does.

[Mahler9th]

Interesting....

regarding 964 as a track/race car... my comments are valid. Cars that are more modern and heavier are BY DEFINITION more expensive to run. The modern part of the equation results in more complex service and maintenance. For example, try changing the plugs on a stock 964 versus an earlier car-- even one with a 3.6. And often (not always) the modifications necessary are more expensive. The braking comments are particulalry interesting. Those big brakes work well, but they also weigh quite a bit.

From a racing standpoint we have very few/zero running 964 based cars up here in Norcal. And only a handful doing "track days." There is a reason for that. I think they are great cars, but they are not the optimal starting point from a $$ perspective.

On the topic of lsds, also some interesting commentary. A lot of pros do not like tbds compared to more conventional lsds, but there are trade-offs. My cars has a tbd and I get some wheel spin at a couple of important corners at our local tracks. In some ways an lsd would be better. In some ways not. I guess the same is true for a locker. So I have come to think of these hings (like many others) as kind of a continuum, with trade-offs that should be considered. When I begin to examine trade-offs, I always consult real pro racers. We have such great access in the Porsche world that it is pretty easy to ather good information to make decisions$$$$.

[Bill Verburg]

Mark Donahue was a huge fan of the locked differential and, to read the article, folks shouldn't even bother to make a Torque Basing differentials.

A locker needs a lot more power to be useful than most of our cars have. A locker is also not at all desirable on a street car which by it's very nature is compromised for track purposes.

A ZF type is far more desirable for track use because of it's enhancement of stability under braking.

my 915 40% ZF is great for street

my stock 993 20/40 lsd is worn out and will be replaced by a 40/60 Guard unit. The Cup and RS cars I have driven w/ that setup have been fabulous.

I agree when purchasing a used lsd be sure that it is functioning, the difference is astounding.

[Ho Hum 74]

I think most people are scared of 964s becuase of the perceived issues regarding them (head gaskets, flywheel, distributors etc). Most forget that the RS Americas are VERY competitive in D class with the 964 cup being the C class killer.

As for brakes, the 964 has smaller brakes than the 944TS and S2 with M030 package, so I don't know where you are coming from when you say the brakes are too heavy. Actually they are just about perfect for the car and the kinetic energy it can generate.

The 964 weighs about the same as the 944T/S2 so a similar level of consumables budget is needed. What other D, E or F cars did you have in mind that were less on consumables? My 1974 911 runs in E and I agree, at 2,400# is rather light on tires and brakes but the 964 is more reliable and therefore contributes more to driving fun and focus. Either way it is a trade-off. There are no light, modern Porsches to race on a small budget. To knock the 964 is to overlook one of the finest and cost effective 911s. Remember the 964 sells for about $10k less than it's 993 counterpart and the 993 is not a $10k better car.

Tristan

[Don Plumley]

I'd prefer more 964 bashing while I look for one to buy!

Yup, they are awful. Can't imagine why anyone would want one. Someone should pay me to take theirs....

[Geary]

A torque-biasing diff in a track car will eventually fry itself -- even the GT brand. A pro team can fry one in a single test session. Longevity aside, not a single pro team uses a TBD for good reason. Lap times are quicker with an LSD.