LSD Setup Thoughts for Leeloo, Figuring out the choices Options

[nine14cats]

Hey Guys,

I need some advice for Doris' car on Limited Slips.

We are putting the car down for the winter as it is getting some mods done over the next couple of months and I need to dismantle some of the car.

Mods are:

1. Going to TCDesign in Sept/Oct for new cage with door bars for safety. The bolt in cage has the door bars too low to help with a collision. At the same time I will have Tony tie in the shock towers front and rear and add chassis stiffening. The cage will also be NASA/PCA Racing legal without using a Petty bar, which makes it more comfortable inside the car.

2. Roger Sheridan is making me up his lightweight front and rear lids along with a new targa top that will allow more room for Tony's cage. At this point I plan on going back in with the dash, door panels, and some carpeting to make the car more "stealth".

3. I have ordered 21mm hollow T-bars for the car and I have plenty of springs in the garage to try. I may bump the spring rate in back up a tad to 275lbs/300lbs from the current 250lbs to help with turning and then with the softer front end I can get some Anti Roll bar adjustability back as I have the front bar full soft and it still pushes. The car is way too stiff in front.

4. We are going to bias ply slicks for the setup. We will use R35 / R45 compound Hoosiers for AX/track and eventually move to Avons for AX.

I'll also redo shock valving after I figure out the T-bar/rear spring rates. At that time I will have the spindles raised.

That brings me to a limited slip/trans combo. Doris hates the 901 and remembers the 915 we had in our 930 (I had swapped the 930 4 speed for a 915 5 speed which was much nicer to drive around town). She liked that trans. I have a 915 box and will spring for a WEVO kit and flipping the R&P. So now I need to decide on a limited slip. The hot AX ticket is a Torsen style but it offers no help under braking on the track. I really liked the feel of our ZF style Guard on our previous 914-6 as you can feel it settle the rear end under braking in high speed situations. It made the car easier to drive. Since Doris will be driving the heck out of the car at DE's, I'm thinking a 40/60 clutch style from Guard. 40% lock up under power and 60% lock up under braking. That should tame the car in braking Thill or BW and still make the car hookup out of slow corners.

What do you guys think? I'm trying to setup the car for her to enjoy and not make it a stiff race car like I would drive.

Thanks,

Bill P.

[nine14cats]

A very helpful difference in the design of the clutch type is under braking. There is a ramp rate for locking up the rear wheels where they track straight together. At track speeds entering braking zones you can really feel it in the rear end. A lot of the wiggle you may feel goes away.

On a TBD, under braking it acts like an open diff, because it is designed to do just that, be open. You only feel it under acceleration.

Entering high speed turns such as THill's turn 1, 10 and 14 and BW's Star Mazda can be felt. That being said, many classes of cars, including Spec Boxster, do not allow Limited Slip's, so it is something that becomes a skill thing as you have to navigate the braking techniques as well as the acceleration / throttle techniques. Having had a clutch LSD before, it does make the car much easier to drive on the track. I feel it more on the decel than the acceleration.

Randal,

Maybe on a hill climb your car is so balanced already and since you are going up hill the car brakes and tracks very well due to the inherent gravity forces of going up hill and slows down easier and quicker?

All I know is that on a track it's pretty nice. (IMG:style_emoticons/default/laugh.gif) But a TBD would still help on the track and with the slicks on Leeloo, she will be getting some good grip, so it may not be that big of a deal, especially for Doris, who is a much smoother braker than I am.

Bill P.