torsion bars, what to do.....

[blucille]

so, my '73 hotrod, RS clone....built-up 3.0, will spend some time on the track, but mostly used for road events.....is apart for the winter, carb work, suspension refresh....

the previous owners (at least the past 2, maybe 3) seemed to have done some upgrades, but cut some corners at times, probably to save money....

I found the right rear was sitting too low, I found a set of used SC spring plates....new torsion bar bushings, was told the t-bars were upgraded at some point in the past....I'll do the fronts next, so soon I will find out what's up there.

I found the rears are most likely sway-away solid 30mm bars, I was hoping for something a bit more exciting, hollow bars, elephant racing, I dunno....should I leave them alone, or do the upgrade while it is all apart?

Yes, the budget concerns me.

Lewis

[Chuck Miller]

Lewis,

In my estimation 30's are plenty for your rears...

I ran stock 19 x 23, then went to 21 x 26 (usual 1st step up-grade) and now on 22 x 29 ......

My new set-up is just fine for street and track for me........ and I don't drag my feet...

[Flieger]

Leave 'em.

[Kaleid]

Chuck,

Do you know if the 19 front/23 rear stock configuration is right for all 69-73 models? Curious what the 70E I'm restoring needs.

Thanks,
Marco

[Chuck Miller]

Do you know if the 19 front/23 rear stock configuration is right for all 69-73 models? Curious what the 70E I'm restoring needs.

Marco,
All that I have heard and read ... yes

Hope this helps

[Macroni]

I would put together a strategy and do it once.

[blucille]

I would put together a strategy and do it once.

What ?

I've never seen a project that you've only done once

[a911s]

Chuck,

Do you know if the 19 front/23 rear stock configuration is right for all 69-73 models? Curious what the 70E I'm restoring needs.

Thanks,
Marco

19mm torsion bars were used on the front of stock '69-'89 911s
23mm torsion bars were used on the rear of stock '65-'78 (or '80 depending on who you talk to) 911s

So, Chuck is right.

I also like Marco's (Mr9146) suggestion of using soft torsion bars and heavy sway bars. I had 23/31 torsion bars on my T/ST for competition purposes, but went to 21/29 when I converted it to street use. Worked fine with my TRG sway bars at five track events last year.

Just don't ask me about Turbo brakes...

[Flieger]

The stiff sway bars and soft torsion bars will be a compromise for both realms. The soft ride will only happen if you take a speed bump head on. If you hit a pot hole with one wheel lets say or the bump is not hitting both wheels at the same time then the anti-sway bar will come into play and the ride will be stiffer than the torsion bars themselves would be.

Furthermore, you will either be way overdamped in pitch and heave or way underdamped in roll, or a little of both. This means that if you want to be underdamped for a nice highway ride then when you take a quick chicane the car may become unsettled if you get near the natural frequency. Luckily the stiffer bars will mean that frequency is higher but still more damping would be nice to have in case you need to make a quick correction like from a slide/spin.

Torsion bars should be the ones resisting the roll for the most part (say 90%). Keep the wheel rates in balance with the weight distribution for nicer heave behavior. Valve the dampers for those torsion bars. Then add an anti-sway bar to balance the under/oversteer.

[a911s]

Theory is one thing..

My car actually performed better and felt much more controllable at autocross last season with the softer T bar set up. I never even softened my adjustable sway bars which are the medium (B) TRG bars set in the middle of the range.