Coilovers with torsion bars?

[mrm930]

Hello everyone,
Long project continues. 78-930 Started as a rolling chassis with "tub-up" restoration. Not restoring it to factory original - alot of custom items. Motor has a great deal of mods - should put it between 400 and 450 (maybe). Custom interior from Classic 9 Leather, turbo, injector blocks and other fuel/air mods from Chris at Turbokraft.

So - I am getting to the suspension in a few months. On Rebel Racing site, Clint, notes the use of coilovers with torsion bars. I called and emailed Clint, but have not heard anything yet. Does anyone know what is preferred or how that works. I am going to lower the car - bump steer and the lot. Plan on using the Polybronze bearings and various other parts from Elephant Racing. Maybe the ASP plates also from Elephant Racing.

Any input from the ones in the know is appreciated.

Thanks, Mark

10 - Cayenne GTS (hers)
11- GT3 (wife said ok to order this year)
78 930 - 3.2 C&R, twin plug, heads ported and polished, nirest rings, Extrude Hone, Euro racing fuel head, Euro injectors, Turbokraft Garrett 35R turbo, Turbokraft longneck intercooler, Billet injector blocks, crankfire ignition, Grubbe B cams, 1.0 bar wastegate, stainless steel headers and exhaust (powerhaus), low mass clutch and billet pressure plate, 6 injector WMI (snow performance), std powder coat stuff.

[mrm930]

Sorry.
Forgot to clarify. Car is mostly just for the street with occasional DE. I don't want a full race ready suspension - it needs to handle very responsively, but can have a more aggressive ride. Not a kidney replacement type of ride. So - a soft race suspension. Do not know how to correctly term this.

Mark

[cole930]

Mark,

Just finished doing this last week. I pulled the control arms and spring plate to install new bushings in both. When I put it back together I indexed the torsion bars to 20* and added Billstein Sports with Rebel Racing adjustable 200lb. coilovers. I just street the car but wanted to eliminate the Turbo squat and also be able to adjust the ride heigth without pulling the spring plates. The best of both worlds. I would also suggest replacing the front swaybar with a 22MM to help balance it back out. No engine and 6" of snow keeps me from doing a road report. From everything I've read everyone that has done it has nothing but good things to say about the mod.

Cole

[Flieger]

Well, Clint might be more responsive if you used his parts like bearings.

I basically represent Clint on the forums, so if you can't get ahold of him, send me an email. maxsluiter@earthlink.net

Are you talking about using torsion bars in the front and coil springs in the rear? Or coil springs in the rear while retaining the torsion bars? Either case is perfectly fine. The original RSR used torsion bars in the rear for regulations, with coil "helper springs" which probably were stiffer than the torsion bar "main springs". Coil springs in the rear should be used in conjunction with some reinforcement on the cross member where the damper mounts, because the loads of supporting the car are now going through there, rather than the torsion tube. Of course, retaining the torsion bars takes some load off the coils and so the reinforcement may not be needed, especially on a street car with street tires.

Torsion bars in the front is fine. The weight is low and ride height adjustment is already easy.

Coil springs have a greater range of spring rates and can be much stiffer. The 2.25" diameter springs from Clint are smaller so that tire clearance is not much of an issue, but there is still less than with torsion bars if you have a narrow car and want wide tires.

For the rear, if you go coil springs, it is nice to take out the torsion bars, thereby allowing you to use the 935 spring plate for more adjustability of wheel alignment, as well as available anti-squat geometry.

hope that helps

[cole930]

Mark,

Never let it be said I would dispute "anything" Flieger offered in the way of suspension advice " here he is considered to be the suspension God".

I just wanted to add I had done a lot of referencing as to the need for reinforced shock towers before I decided to do this and the general concensis was reinforcement would not be needed in my application.

It's a street driven car and when using a 200lb. (light springs) in conjunction with
the torsion bars reinforcement would not be needed.

Thought you might appreciate a look: Function with a little cool factor thrown in.







Cole

[Miguel Antonett]

Flieger is on the money............... I would reinforce the towers to go with the coils and get rid of the TBs. I believe that together they work against each other - sometimes, and sometimes together so...

[xbmwguy]

I am currently running stock rear torsions and clients set up with 250# springs, another nice thing about this set op is going to the track use a 250# back to street go 200. It's stupid easy to swap and like Cole said height adj is super easy

[mrm930]

Okay, so lets bottom line this. What are the numbers here? I do not want a hard racing ride. My daily driver (except when it snows) is a 2010 BMW M5. There are multiple settings for shock stiffness, shifting rates and even HP. You push the "M" button and the your whole preset goes void and it sets up to a racing mode. Even with the weight of that car, the suspension set-up is uber stiff in the M mode. Handles the car with that weight, 510 HP and suspension to match, however to drive that constantly would not be pleasant. So I need something that is comfortable on the street yet aggressive when I need it. Too bad there isn't an electronic product made to switch back and forth like the M cars.

Keep in mind that I am going to lower the car.

-Rear
-Torsion bar size when used with springs? What size springs and what rating on the shocks? New spring plate: RSR or the Elephant Racing ASP? What size sway bar?

-Front:
-Use the torsion bars, if so what size? No coilovers? What size sway bar. I need to have raised spindles on the front. I am thinking 40mm - wheel size is 17s. I am using a set of RUFs that I bought new in the 80s.

I will also try Clint again. Can't leave voice mail because its full. Try again online.

Thanks again guys.

Mark

[RarlyL8]

I want to do this as well.
How do you adjust ride height?
How much adjustment is there?

[911st]

My two cents:

I am not a fan of mixing springs at the rear.

The factory probably would never have considered this if it was a way around the race rules at the time.

Complications from doing this could be poor front to rear spring wheel rate balance and difficulty getting a proper 'dynamic' corner balance. If one insists on going this way they probably should not only use scales but also do a wheel lift balance test. Especially if the rear coil overs are progressive for any reason. (Any rubber bushings at the shock ends may even make the rate somewhat progressive with lighter rate helper springs.)

For a street car there is a significant selection of stiffer rear torsion bars to fit even the most aggressive DE/street user that coil over's are not really needed.

Nothing wrong with a torsion bar front w a full rear coil over rear conversion if done right.

As to ease of adjustment, a set of good adjustable rear arms are not far behind and for most and can ease rear bushing replacement. Even then, once it is set most street users are not going to be making a lot of ride height changes anyway.

I might spend that money elsewhere like on custom valved shocks, adjustable sway bars, raised / decambered front spindles, or even track fees first.

[Rodsrsr]

With 29mm rear bars, I was still getting enough squat to scrape the rear tires. A set of Rebel Racings 150 lb coil over helper springs solved the problem. As far as adjusting ride height, I don't think so because there should not be that much tension on the coil in a normal position. T-bar adjustment takes precedence. I ran these with unreinforced shock towers for years with no issues however I recently added the shock tower mounts only because I had my engine out anyway.

[mrm930]

Now I am getting more confused at the options. Springs - yes/no with or without TB, etc. Need to do more research on this.

Everyone please chime in - no wrong answers here. Just curious about your set-ups and how they are working for you.

MRM

[Flieger]

You will never get a 930 to have an M button without spending lots of money retrofitting a 997 PASM to it.

You can come close using some tricks.

Firstly, a spring is basically a spring. Mixing torsion bars and coil-overs in parallel is no problem. Yes, the rates are different curves, but you can tune them for the effective rate you want, which is a progressive one from the sound of it. Soft for a little bit of roll and bump absorption and then hard for when you are really going fast. This can also be approximated with two coil springs in series. One is softer and when not coil-bound makes a soft total rate. The other is stiffer and causes a step up to a stiff spring rate when the soft coil bottoms out. This tuning will be most effective if the coils are doing a larger percentage of the work than the torsion bars.

The M button I believe only changes the dampers, not the spring rates. This can be approximated by using 4-way adjustable dampers or by using digressive valving. Make the high speed bump and rebound softer than the low speed. This stiffer low speed valving would provide most of what you want, even without extremely stiff springs. On a skidpad or long sweeping turns, you would need stiffer sway bars to control body roll with just the dampers and without the stiffer springs.

Again, the nice thing about full coil-overs in the rear is the 935 spring plate for better geometry, adjustability, and anti-squat. If you have only coils in front, you can use the 935 front suspension, but that is harder to get unless you make your own version. Torsion bars are fine for the front, unless you want to do them "while you are in there" in anticipation of racing the car int he future and needing stiffer spring rates.

I will get Clint to contact you. He has coil springs all around on his car and can give you his experience.

[cole930]

Mark,

The straight scoop !!!!! If you are not going to race, race, the car and you might dink around with a DE or parking lot you simply don't need a bunch of trick sh--. We all can do that with the stock suspension and have a lot of fun.

Ask yourself how you want to use the car. I did this mod for 2 reasons. I wanted to be able to control squat and I wanted to be capable of adjusting ride heigth without reindexing. I don't need corner balancing balancing, larger T bars,
or different front T bars to do that.

I'm running stock T bars front and rear and went over this with Clint to confirm what I should do. His only suggestion was to up the front sway bars to 22mm to balance out the effect of the added springs on steering and get an alignment once everything was finished. I specifically told Clint I did not want a harsh ride and exactly why I was doing this.

The coilovers make the shocks adjustable so you can adjust in or out the added spring rate anytime you want by jacking up the rear end and readjusting the collar position. If you don't like it crawl under it and dial all the tension out of the coils or just take the coilovers off and sell them. No need to over complicate this.

Cole

[RarlyL8]

I need the ability to adjust ride hight and reduce squat. No way in hell I'm putting bigger T-bars in. BTDT hate it. Last time I changed the rear shocks the ride height went up 1/2"! Re-indexing is the biggest PITA. For my application this looks like the perfect solution to these issues.
So how do you adjust ride height?
How do you determine what spring rate you need?

[Flieger]

(By the way, I talked to Clint a few minutes ago and let him know about Mark. He found the emails had gone into the "spam" folder for some reason but he read them and was going to call Mark ASAP.)

[mrm930]

Thanks Flieger, good info.

I know - just talking out loud about the M button. I am sure that the newer 911 versions will probably have some kind of electronic dampening and other settings, if not already.

However if someone did come up with an electronic dampening system, competitively priced, for a retro fit - that would be very cool. Just talking out loud again.

MRM

[Flieger]

Did he call you? He is busy from 11-2 today so I wanted to call him before then, but it was close to the time he needed to leave.

[full quack]

Use Clint's front control arm bushings, you will absolutely not be sorry, they are the cats meow!
Mark

[Flieger]

Originally Posted by full quack

Use Clint's front control arm bushings, you will absolutely not be sorry, they are the cats meow!
Mark

Yep!