Porsche 911 question: Limited Slip diff - Should I? or not?

[Cyclingpeaks]

O.k.newbie question, I have a 1988 - 911 all ready for racing. It was raced in PCA races from 2002-2006 and now I am the new owner and will go racing this year with her again.

 

I have to pull the engine and tranny to fix the synchros, full oil job, valve adjustment while there, spark plugs, etc. So, I figured while I am there, I could install a limited slip diff- OSD giken was what I was looking at. But, it's $1200.

 

It appears this car doesn't have a limited slip. When elevated, I turn the drivers side wheels forward and passenger side rotates backward. That's the test of it, right?

 

So, my question is: For $1200, how important is it in racing? Will it improve my times significantly? I am running times at VIR and Summit point very close to the pole position for this past year in my class, so I know I'll be competitive.

 

Or, am I better off just using that $1200 for another set of tires this year?

Anyone out there that has lap times before and after and can contribute the limited slip diff to the improvement?

 

Any advice greatly appreciated.

Thanks.

Hunter

[John Graber]

You have to have it. Without it you wil get wheel spin, lose time and kill your tires, especially in a car that weighs say 2800lbs. You can get used units for about $1000 and then replace the disks. Good luck.

[JSG1901]

"Have to have it"? Not sure. "Want to have it"? Yeah.

 

I have an LSD I had rebuilt last year which stopped limiting the slip on about the second weekend out. In other words, if it's working (which it may be), it's not working very well.

 

I don't have a lot of horsepower (about 200), so my car is a lot less likely to spin the tires under any circumstances, but what I found was that as more and more slip came back into the drivetrain I had to clean up my lines. I can't, for instance, put my tires on the curb in the Carousel at Mid-Ohio without spinning the right rear.

 

On the other hand, I've found my laps are faster by having to drive that bit more carefully. Late last year I did my fastest-ever lap at M-O with the not-working-very-well-if-at-all LSD.

 

It sounds like you are already fast and smooth. The more power your car makes, the more you'll want one and, given the choice, you're better off having one than not, but the lack of an effective LSD didn't seem to hold me back a lot last year.

 

If it fits in your budget, do it. If not, it's easy enough to pull a 911 motor. You can always do it later.

 

IMNSHO

[dmwhite]

Will it improve my times significantly?

are you getting inside wheel spin or otherwise having trouble putting power down? if not, then i can't see a new diff making a significant difference...

[Cyclingpeaks]

Thanks guys. That helps. Sounds like it will definitely help me then and worth the expense. I am not getting an excessive amount of wheel spin on the inside wheel, but can feel it happening a bit, say in turn 4 at VIR and turns 5 and 6 at Summit point.

 

I talked with a 911 owner(in my class) at the Nov. Nasa race at Summit point and he had one and said it definitely helped, but haven't heard from anyone else about it.

 

Thanks.

Hunter

[944-Spec#94]

Yes a limited slip will help. It will help on corner exit and also on corner entry under braking.

 

A good diff is way to improve handling.

 

That said you can race without one and you can adjust the chassis to reduce wheelspin. Sure you will give up something, but you can still have fun and race hard.

 

BTW... I have run my 944 NA for years with an open diff. I want an LSD, the cost makes it hard to get. Over the years I have learned to overcome the open diff such that I minimize the impact, but am fully aware I am giving up something. The hard part is quantify that impact.

[116svvh]

A good working limited slip will help as much under braking as it will anywhere else. If your 911 was like my 993, it got tail happy under heavy braking. With a working LSD, my car would brake straight and I could even use it for trail braking effectively. Not so much with the worn out LSD. Spend the moeny, I think it was well worth it and mine cost me more than the price your quoted by the time I paid to have it set up and installed.

[cstreit911]

It's a must have when you wanna go fast!