Coilovers vs torsion bars questions

[e p slick]

First of all I acknowledge I have no idea what I am doing - strictly shade tree mechanic skill level. Secondly here is what I am trying to do: Drive 95 miles in Silver State Challenge open road event on Nevada state highway (closed and sanctioned by Nevada State Police - its legal) at a spot-on average of 175MPH.
Car HP, weight, gearing (.595 5th gear) etc make this possible on paper. However - I need input on suspension set-up. I have gathered various components for this project and now need to determine which to utilize. Car has 30 and 23 torsion bars + Bilstein coilovers on the front. I just picked up a set of Bilstein coil overs for the rear and now attempting to determine what path to take - thus my request for input. I have heard that when utilizing coilovers one usually deletes the torsion bars. I have also heard the opposite - keep the torsion bars when using coilovers. The course I will be driving has no particularly sharp turns but rather sweeping curves along with straight sections. There is a center crown to the road as it is used as a public highway 364 days a year. I have driven in this event in the past with a 911 (140MPH average) and my stock 930 (160MPH average). Curious to learn about combinations suggested along with spring rates. Appreciate the opinions. EPS

[jluetjen]

Coilovers are just another form of spring, just like T-bars. You can use them instead of, or in addition to the T-bars. It just depends on what you are trying to accomplish. Wether coil-overs are an improvement overe T-bars depends on the following:

- Desired spring rate
- Tire size, traction and G-loading expected.
- Suspension geometry (including if the car has been lowered, and by what method was it lowered).
- Tire size, track width and space available.

[911ctS]

Oh man! I've always wanted to go see that silver state challenge, or maybe do it myself. Have to gear up for top speed though.

To help with your question. I think when making the switch to coil overs most people go all the way and delete the T-bars. However there are some applications that would favor running both in order to increase spring rates. The 934.5's were factory built race cars that used this method of T-bars along with coil springs. Many high HP 930's use both as well. Spring rates available for coil springs pretty much cover everything you could possibly need, so having both is not mandatory for a full race application. The main advantage of totally deleting the T-bars on a dual system car is the weight savings. Other than that, the conversion could be done is stages: First adding the C.O.'s with helpers. Then later upgrading to heavy rate springs with T-bars removed and some reinforcements added to the chassis. After that it would be onto 935 style susp. to replace the bulky A arms, F/R bushings, and rear spring plates.

In your situation it would be very inexpensive to add some helper springs in order to achieve more spring rate. Although depending on you car im not sure you need all this for the silver state challenge. What chassis will you be using this year and how much HP you expect to have?

[lateapex911]

One of the big benefits to a true coil over setup is the ease of cornerweighting and spring changes, both important when you race.

But you're doing ONE event, and it's a very narrow application. I frankly don't see the need for coilovers, really.

What I DO see the need for is;

Great areo. (And thats not in terms of downforce, but more in terms of balance.

Horsepower. You'll need lots. And then some more.

IF you have time and money to burn after those issues (not to mention saftey devices) then consider switching to coilovers, but remember, if you DO go with a coilover setup, you HAVE to add structure to the new spring pickup points, unless you go with small "helper" springs, as mentioned above, to help fine tune the T-bars.

I'd think a great setup would be stiffer T-bars, dampers to match (adjustable!) a Wevo SPS system for the rear, with mono balls, and Elephant Racing's Polybronze setup for the front, with Smart Racing sway bars at both ends. Plenty of adjustment will be available, and corner weighting will be a walk in the park, should it be needed. Just be sure to get dampers with rates appropriate for the springs, and I'd REALLY want some further damper rate adjustability as well...two way minimum.

[crashmy911]

You need YEllow Bird!!!