Unique Suspension Situation

My 73 911 currently has a modestly upgraded suspension, to accommodate an engine that weighs 100 pounds more than the original 2.4 liter. I have stock 18.8 mm torsion bars in front, and 26 mm torsion bars in back. I have Bilstein sport shocks in front (in Boge struts) and adjustable Konis in the back. I have 22mm sway bars front and back, currently full stiff in back and full soft in front, since the car initially tended to understeer. I have 8-inch wheels with 245 tires in back, and 7-inch wheels with 205 tires in front.

My next big upgrade is to put brakes from an 86 Turbo on the car, along with aluminum trailing A-arms (from a 74) in the back. At the same time, I'll probably do the turbo tie rod upgrade, and -- since I think I could tolerate a slightly stiffer suspension, I was thinking of maybe putting in thicker torsion bars at the same time.

My question: with the light weight of the 73 tub, and the slightly-unusual weight distribution of my car (it's more than 60 percent in the back, but I forget the exact numbers), what would be a good torsion bar combination for this car.

A lot of guys go to 28/22 for track use. Does this make sense for me? Or would 21 be more appropriate in the front of a lighter car? Any opinions?

In case anyone wants to analyze body roll, here are two pictures of the car at pretty much the maximum of its cornering ability (with street tires):

http://members.rennlist.com/jackolsen/TrackPhoto.jpg

http://members.rennlist.com/jackolsen/TrackPhoto2.jpg

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Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net

[This message has been edited by JackOlsen (edited 01-26-2001).]

Jack:
I also run my car on track w/23f & 33r torsion bars. Adjustable sway bars at both end too. I installed them not long after I bought the car. Probably after one slalom. Since then the boby roll is much less and better control of under/oversteer. How does your car feel now? Have you done corner balance? Since you live in L.A., there's a shop in Torrance called Suspension Specialties by Steve Alarcon. He knows and races Porsche. I think it's a good idea to get his opinion.
p.s. I don't know him personally nor he set up my car, but fellow racers recommend him and satisfy with his work.
Andy
'87 Carrera

Jack,
The bananas(semi-trailing arms) are the ones made from Al. on the newer cars, '74 is fine. As long as you're replacing the semi-trailing arms why not replace the trailing arms at the same time, the 2 piece adjustable ones from a '77 up are preferable, be sure to inspect and replace the bushings as necessary, if the car is mostly street driven I would stick with rubber bushings (Neatrix or factory). 22 & 28 mm torsion bars will not be too bad(not a lot of potholed roads in CA), the gun drilled ones are a bit lighter and reportedly have better reaction times. Fine tune the handling with adjustable sway bars. I would/did replace all shocks with the Bilstein sports, they are necessary to match the heavier bars, especially with bigger/heavier tires.
I'm sure you didn't forget that a 23mm mc will be necessary for the 930 brakes.

Jack,

Those pictures don't look bad at all for stock 18.8 mm bars up front! I bet the 21 mm bars would work just fine, as I assume you still want to keep the street ride quality somewhat 'reasonable' ...

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Warren Hall
1973 911S Targa

I've done 22 and 28 in mine with Bilstein Sport Shocks and adjustable 22mm sway bars front and rear. IMHO 23 and 33 is too stiff for any amount of street driving. Also, unless you have race dampened shocks, these bars may be too much and bouncing may occur. I would go 22 and 28, maybe 29 in the back. You want your torsion bars to be in tune with your shocks. The sway bars can then tune the body roll and over-understeer. Don't forget adjustable spring plates for corner balancing.

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8 9 9 1 1, The last of the line.

Steve Alarcon aligned the car, corner balanced it, and set up the current suspension. I'll be talking to him about the brake upgrade (to see if he can do the work on it, in fact), but all of this input is helpful.

Bill, I will be doing the Mercedes master cylinder upgrade, and -- depending on Steve's input -- will probably have VCI do the machinine work for the calipers, as well as use their custom rotor set-up for the front.

28/21 is what I'm currently thinking for the torsion bars. I'll ask Steve for his suggestions on that, too.

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Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net

Your getting some good advice!

You have a beautiful car, Jack. And I was REALLY entertained when you kept us posted months ago during your initial track 'dial-in.' Wish I could help you with advice here. No real expertise.

Interrestingly though, I have had daydreams about the relationship between shocks and torsion bars (my daydreams are not the usual kind). If torsion bars get stiffer, I suspect a car could develop bounciness, perhaps even the 'launch' kind that can be real unstable where the road has severe short rises and falls, particularly in turns. I suspect that the shock needs to be dialed stiffer to properly manage the more energetic torsion bar. Make sense?

I think this might be more important in the rear. I think your shocks are adjustable.

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'83 SC

More suspension daydreams. Jack, it sounds like you're about to do two things that I would like to do up front. What I mean is, stiffer torsion bars and turbo tie rods are are important upgrades that give you lots of bang. Particularly torsion bars. I think Bruce Anderson likes the torsion bar upgrade as a start. It will reduce sway, and will stabilize and firm up handling without too much objectionable side effects. Sway bars and shocks do more to harshen the ride, than torsion bar upgrades. So, I think you will be pleased.

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'83 SC