Time for torsion bars on my 930

[David]

I'm in the process of installing ERP bushings and monoballs on my rear suspension and I found I have stock rear torsion bars so it's time to spend more money.

What I have:
79 930
2750 lbs
~500hp
22mm Weltmeister sway bars front and rear
Bilstein Sport front struts (about 500 miles on them)

What's in the near future:
ERP bushings all around
255/40-17 tires on 17x9" front
315/35-17 tires on 17x11" rear
22mm front Sander solid torsion bars?
31mm rear Sander hollow torsion bars?
Bilstein Sport or Rally Sport rear shocks? (what is an RS shock?)

This is a Sunday afternoon good weather car and soon to be DE car. I don't mind a stiff suspension. I'm trying to decide on these last three items, the bars and shocks, mainly the rear torsion bars since I need to order them on Monday. Any thoughts and comments are appreciated.

[beepbeep]

Why not coilovers? That would open interesting oportunities should you decide to go for G50 tranny...

[jmz]

David,

Did you finish the engine?

I also think you should consider coil-overs. I never considered them for my car but having recently ridden in a '72 RS body car set up w/ coil-overs, 930 trailing arms, RSR Struts w/ coil-springs I wish I had. This car had 3.6, G50 and man was it impressive. It was tight, handled well, it was REALY LOW and it was comfortable just putting around too.

By the way it lives in Clear Lake too.

For what it's worth, I went with sports on the rear of mine and am happy with them so far.

[350HP930]

I am going with 22/28 or 22/29 t-bars on my car.

[David]

The engine is together. I still need to put on the shroud, intake, and ignition system. I've run new fuel lines and now I'm rebuilding the rear suspension in preperation for the engine.

For a car that will be mostly driven on the street, I can't justify the extra expense of the coilovers. I would really like some Fox Shox or JRZ's or something like that but I can't see spending $3000 to $4000 for them. I've done many things I wasn't planning to do on this project but I've got to draw the line somewhere.

[Randy Blaylock]

I have 418 hp to the wheels in a 2650 lb 930 that's street driven and a track day car. It has a six point cage, 17 x 10 and 11.5 wheels running 275 and 315 R compounds.

It has 24mm/33mm torsion bars, and 150 lb coils on the rear shocks to help with squat under acceleration.

Once you get the suspension set up and run large tires with lots of grip, you'll find that you almost can't get enough spring rate with torsion bars.

The car will be pitching all over the place transferring weight side to side, diving under braking and squatting under acceleration. This is especially noticable at tight tracks like Sears Point. Keep in mind that you want the springs primarily, and the shocks, to control weight transfer. The sway bars are to tune the balance of the chassis.

It's not the springs that cause harshness in the ride, it's the shock valving and bushings, and you are wisely using Chuck's fantastic products. The curious side effect of having these near zero stiction bushings is that without the bind in the suspension, the chassis is actually more likely to need more spring rate than before.

You'll also need more spring rate in a car without a cage because the chassis flex gives up some of the rate.

Coil-overs are a bad idea in a track driven car with stiffer spring rates unless you reinforce the shock mounts, the rear truss where they mount, and the front towers. Ideally, you'll tie these points to a cage. It's not a question of if, but when, sheetmetal will begin to tear.

I'd recommend you go with a 24/33 package given your application and the other upgrades.

[350HP930]

Originally posted by Randy Blaylock
Once you get the suspension set up and run large tires with lots of grip, you'll find that you almost can't get enough spring rate with torsion bars.

Well, you can get all the rate you want, it just isn't progressive which is the only advantage of coils besides availability that I can think of.

[Randy Blaylock]

I'll have to repectfully disagree on the point of available spring rate in torsion bars. Even with the maximum sizes available, a cage that adds rigidity to the chassis, and additional coils, my car still has too much pitch and roll.

I could convert to coil-overs but that involves a bunch of other issues to be done properly.

FWIW, most common standard coils are not progressive, they are linear.

Kits that have a main and a tender spring also usually have two separate linear spring rates.

Progressive springs are used where the performance is intentionally compromised towards comfort, the initial rate being light for compliance, steadily growing firmer for bottoming resisitance. They can be identified by differential coil spacing (most common) or progressive wire diameter.

[jmz]

Here ya go David,

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/212800-911-suspension-parts-srp-anti-roll-bars-coil-overs-torsion-bars.html#post1828584

[David]

Thanks for the link on the shocks, but if I go with coilovers I'll go with full adjustable ones. I'm trying to avoid turning this car into a race car since I'd prefer to spend that money on a race car.

The biggest front bars I'd try is 23mm since I'm not a fan of understeer. I'll probably get the 22mm fronts and adjust with the sway bars. The decision I need to make for Monday is whether to order 31, 32, or 33mm rear bars.

[Jeff Alton]

For tosion bars I would use the ones from Chuck at Elephant Racing. Cad plated and with a rubber plug to keep moisture out of the center. I have used these and they are excellent. I have used sanders as well, but they are out of stock often with long waits. I recently put TRG coilovers and 935 front and rear pieces in and am very happy with them.
Total overkill for my car, but they are great.

Jeff

[David]

I noticed that Elephant Racing has the hollow torsion bars. Chuck, I'm curious what the material, hardness, and actual diameter is on your 31mm bars.

[jmz]

Chucks are Sanders bars.

[89turbocabmike]

David, I'm running 22/31 hollow sanders bars on my cab which weighs 3100lbs. These were on recommendation from Steve@rennsport. Just right for my 95% street car. I'm currently running HD/sports but currently have Jae at mirage doing some custom ones and raised spindles. The HD's have a soft ride but can't control the 22's. Sports up front had too much compression. Sports work well with the 31mm, but there's some improvement to be had with revalving. Talk to Jhunter on one of the turbo boards, he was running 23mm fronts on a similar weighing coupe and they were too harsh for street.

[dickster]

i also have the 22/31 setup on my coupe. i like it so far. the bilstein sports seem to just about cope.

its as stiff as i'd want to go for the street. its a little "flighty" for uneven back roads, but okay. on a decent raod its like a go kart.

i would recommend it for a street/track car.

what did ya go for?

[Wil Ferch]

I have to agree with Randy.....the torsion bar selection will be...at some point...limited to the spline diameter you have, and not much more spring can be had beyond this.

Randy's car, as an example....would need "wheel rates" in excess of what the largest torsion bars give, noting the spline diameter limitation.

Do also understand the 4th power relationship to stiffness for each increment increase in diameter.... pretty steep.

Wil

[David]

I went ahead and bought some 31mm bars from Chuck. I'll get 22mm front bars and Elephant Racing bushings if I ever finish all the work at the back of the car... 10 months and counting

[dd74]

Good thread.

[David]

With the never ending quest for weight reduction, I thought folks would be interested to know the 31mm (actually 32mm) hollow Elephant Racing bars are a bit lighter than the stock 26mm bars.

[350HP930]

Thats good to hear since I was also planning on running hollow rear bars in order to trim a few extra pounds off the rear.