911 Torsion Bar sizing ... input please

Hi Sean,

I had a 66 911 that i auto-xed. When i cranked in a bunch of negative front camber i got a lot of darting. This was particularly noticeable with slicks. I had to get out to the track somehow
chris

 

The torsion bars were stock but i had a 19mm front and 17mm back sway bar. It used to 3 wheel it around relatively slow turns.
FUN car,
chris

 

Lucky- He is talking about the anti-roll bars, not the torsion bars.

Taz
Terry Phillips

 

Often "dartiness" is a result of running some toe out in the front. Most serious autocrossers and many many Porsches use some toe out in the front to help the car turn in. The 911 needs it because of the rear engine inertia tends to slow down the transient response. This trick has been around and used on 911's since the 60's. With some toe out the car comes alive on the track...

If the car is "tramlining" (darting side to side) on pavement that isn't even or asphalt that has seen heavy truck traffic and has two wear tracks in then a quick check of the toe setting is in order. Negative camber in the front, will do it to a lesser extent, but some toe out sounds more like what you've got. The sway bars and shocks won't cause the problems you've described.

 

+1 on the toe out. Get some strings and check that first.

Scott

 

Sean,

Wasn't that a championship winning auto-x car set up perfect for auto-x? Don't go backwards and try and make it like the ferrari you are familiar with. If it is a proven winner learn to drive it instead. You could be rewarded. It took me 5 race weekends to feel comfortable in the Z06 and stop wishing for the 348 racecar...then the next two races I'm the fastest guy on the track. Gee I hope that trend continues.

 

I'd start out by looking for slop in the steering joints. Excess play in tie rod ends, for example, will cause the steering to want to hunt all over the place and follow ruts/contours of the road. I installed the 911 turbu tie rod kit in my 911 along with a new rack and she drives wonderfully now - very precise. And, yes, lots of negative camber will accentuate the feel of slop in the steering joints.

 

If you are interested in learning how to do your own suspension adjustments I suggest reading How to Make Your Car Handle by Fred Puhn:
http://www.amazon.com/How-Make-Your-Car-Handle/dp/0912656468/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1237466416&sr=8-1

Its old (1976) but the concepts still hold true and certainly apply to your air cooled 911.

Scott

 

Sean,

33mm rear bars are way to big for a street car. Especially an early 911 which should be pretty light and as such can get by with a softer setup. But I don't think that will have any effect on the car being twitchy.

I'd look at a few things. First is the alignment. Get the camber and toe set closer to factory specs and that should help. The other is the offset, and width, of the wheels. Wide wheels with improper offset can also cause a car to move around.

How low is the car? Does the car bump steer? I would guess not as stiff as it is but it's worth asking....

Back to the torsion bars. A really good setup is 22's on the front and then a 28 or 29 on the rear. I'd also suspect that the custon valved shocks may be a little harsh.

Michael

 

I ran 22 and 29 on my 87 911, with -1.0 camber in the front and -1.5 camber in the rear with RUF shocks and stock sway bars, the car was used on the street, track, and autox. Nice compromise...

 

What made you go with more negative camber on the rear? I also have an '87 911 and I have about -1.2 camber front and rear.

Scott

 

Hi Scott,

It all boiled down to preference and experimenting, we kept changing things around until we got around to the preferred setup. I was sharing my car with my best friend who is also my technician on the car.

 

After those ultimate qualifying times are we

You might actually pick up some time going a little softer... it all depends on the track and how smooth it is. But if your primary concern is the absolute best lap times you'll certainly have to give up a comfortable street ride.

When a car is lowered it changes the orientation of the lower control arm and the steering arm (tie rod). In a perfect world the tie rod would be parallel to the ground when the car is sitting. Then as the car goes over bumps the tie rod would arc the same as it (the suspension) goes up and down. If that geometry is f'ed up due to being lowered (to much) when the suspension moves it causes the tire/wheel to change toe as it goes up and down and that causes the steering wheel to be tugged in your hands. Hence the name bump steer.

 

There has been some new parts developed recently for the torsion bar cars to help with bump steer and ride (bolt on vs previously had to be fabricated). If your car is in Oregon perhaps drop by for a consult with Steve at Rennsport Systems or in SO CAL Dave at TRE.

I would add that I have some very very stiff springs on a BMW with high quality shocks and I have an acceptable ride. Smart racing has some fairly new high end shocks that may be more effective at damping those T bars. I think Ohlins makes some as well. Finally some ride ht may help with the ride a bit.