PorschePhD

It all has to do with the rates you use. I do not feel that a AutoX is going to be an issue. It is no where near the abuse that a track car would see.

A930Rocket

At what point driving DE's is the coil overs not advisable?

I'm running in the black/red group and drive the car like there is no tomorrow at the track.

When I set my car up for the track five years ago, I used 23 and 30 torsion bars with Koni Sports in back and Bilsteins HD's in front, adj 22 mm sway bars and urethane bushings (now I would use different bushings and struts/shocks).

It handles pretty darn good, so I can't justify the money switching to coil overs, not to mention what I consider hard stress on the shock towers. It's just sheet metal compared to what I've seen for other cars with coil over or cars retrofitted for coil overs .

PorschePhD

If you are running stints of a 2 hours straight with 800/1000 springs you are in serious trouble. 30-45 stints with 300/400 500/600 weights is not enough to tear the towers apart. You don't want it so stiff that you don't have any give. No give means that power drops right to the wheels and makes traction an issue.

I think it falls under the category of you don't know what you are missing until you try it. It is a completely different feel.

Chet 930

Not long ago I had an opportunity to drive a 78 turbo (with a full coil over set up from TRG) back to back with my 77 turbo (upgraded torsion bars) and everything else being the same. The difference is noticable. I think Stephen is right as far as not knowing what you're missing until you try it. I dont remember what the spring rates where but the car was pleasant to drive on the street and handled pretty nice, better than my 77 anyhow.

DonE

Are you saying that the cost between nice torsion bars, rear helper springs and valved shocks are only a couple hundred dollars different over a coil over kit?

Sway bars are needed whether coil over or torsion bars, so thats a wash.

PorschePhD

Yes sir, you add all the goodies that you would for spring plates, bars, shocks etc and you will find the difference is not that far off. Now I am sure one could nickel and dime th process to death and broaden that delta but the average of both is not that far.

911rudy

My 930 came with coilovers and I can't comment on the difference. I can tell you that it is a scary ride because it feels like it is glued to the road. It is lowered, easy to do by just turning the big nuts, and body lean is not an issue. The springs are OEM Porsche parts but I haven't been able to read the small writing on the uprights. I owned an '87 Carrera with torsion bars and there is a big difference between the two. I haven't tried to but I would think that tuning the corners would be real easy. Squat and nose dive are also not an issue.
Rudy

DonE

Me too and I have torsion bars. Sorry Rudy, I'm not trying to sound like an *** - a torsion bar car that is set up works pretty well too.

Bruce M.

22s in front, 31s in rear, with 200lb helpers; custom valved Bilsteins, Charley bars front and rear.

Little truck-y on bad roads, but sticks pretty good at the track.

Still, I'm curious to feel a similar car with coilovers...

Ed930

If performing a coil-over conversion for street/light track use, do I need to install a stress bar at the front? It seems that now all of the vehicle's weight is sitting at the towers whereas before these points were used only to support the shock absorbers. Can I also rest assured nothing needs to be modified at the back for the type of use I mentioned? Thanks.

PorschePhD

I always recommend a good front bar that stabilizes the towers. The front is reinforced and is not in need of anything

The rear, tell you what. You have an issue and I will personally repair and strengthen that area. If the use is DE/street and the spring weights appropriate then that is my guarantee.

911rudy

Just to follow up on this line of thinking, my car still employes the original torsion bar suspension. The coil-overs are added to the original suspension. This means that it is a fine tuning addition rather than a complete change from the original. I think that anyone that has worked with torsion bar suspension would appreciate the ability to alter ride height and stiffness with the turn of a big nut versus adjusting torsion bars. This is not a referendum on coil-over systems. Be honest though, coil-overs are very user friendly compared to torsion bars. Pick a race track and then factor in the conditions. Coil-overs can be changed with ease, ie; spring rates and length, versus the uncertainty of varying torsion bars. All of this is not a big deal to the average P-car driver. But we constantly judge mods to our cars and this is just one more brick in the wall. Are Big Reds a good addition for the street car? Probably not. But look at the number of owners that have added them. Think of all the guys that want to change wheel size and ride height. It's easy with coil-overs but a pain with torsion bars. I think that if an owner was faced with replacing all of the components of the OEM suspension, he might consider the cost difference a small price to pay for the adjustability. I want to be clear that I am no an advocate for coil-overs but just telling it from my real world point of view. If you look at the history of all race cars you will find one system that has dominated the feild. This is for a reason. Adjustability!
Cheers,

Rudy

38D

I still think the issue is getting the car stiff enough with Tbars. A 31mm Tbar is like a 400# spring....that ain't gonna cut it for hard core track use. This is why you see so many racers thin down the Tbar and use 700# "helpers".

jimculp

OK, thanks for the responses to this. Another thing- would going to coilovers adversely affect the resale value of the car?

viperbob

As with anything, it depends on the buyer.

I have installed numerous coilover kits for 930s. I had a set and tracked an 84 with reckless abandon. I have never seen an issue.

A few things about suspension that might clear some of these mirky waters. First, think of a spring sitting on a scale. Ok, let's say it is a 500lb (this means that for every 500 lbs it sees, it compress 1 inch) spring. So we put a 500 lb weight on it. The spring redues in size by one inch. The scale reads 500 (ignore the spring actual weight) Now we put on a 1000 lb spring and put our 500 lb weight on it. The spring compresses 1/2". But our scale still says 500. Having stiffer or lighter springs has NO effect on the scale or the force on the towers. What matters if the force being applied through the spring. Whatever the weight and force being applied to the car will go though the strut towers regardless of the spring rates, dampeners, etc. The only thing that happens is the amount of movement of the body in relation to the force being applied 1) though a bump, 2) the weight of the vehicle corner of the car, or 3) additional forces from centrifigul forces in a corner (these are all due to spring rates) and the speed at which these occur (this is controlled by the dampeners). Having a stiffer sping meant the body in relation to the force did not move as much. But the chassis saw the entire amount of force regardless of the spring rate. Hope that helps a little.

Remember with the torsion bar the forces being applied between the road on the car were through the a-arms or the rear suspension and body. That force is not translating directly to the shock tower areas. But they can handle it for 99.9% of you. Yes add 800+ HP slicks, and then maybe you have an issue. Take a 930 with even 500 HP and you are fine.

So you do need to install a strut brace of some kind on the front of the car for the shock towers. Other than that, have FUN... Oh and coilovers are SOOOOOOO much better that torsion bars in countless ways....