ST project: suspension setup questions
 

As the project started I gathered lots of parts to complete my suspension. The time has come to start assembling parts on the car so it can be rolled in the paint booth. The car will be Track/street driven. It is being built as a DE type car with no plans of club racing. It must be suitable to drive on the street, not just to and from the track.

I bought a set of Sanders hollow bars in a 22/28 size. While the 28mm bars in the rear should be nice for my 71 tub with a 3.0 in the back I do have some thoughts that might make me want to change the setup.

The front bars are 22 which would match well with the 28s for a stock car. The problem is that my replica has undergone a serious diet and I think I might need to go smaller. The car has a full compliment of fiberglass including the F/R bumpers, hood, fenders, doors and rear decklid.

I have a feeling that the front 22s will be way too stiff for this lightweight early tub with 'glass parts hung on it. I can almost feel the understeer now.

I estimate that the front has lost about a 100 pounds and most likely more. If I assume stock 2200 lbs with a 40/60 weight distribution the front is supporting about 880 lbs. take 100 lbs off this and the 22mm front should be reduced to about 19.4 mm - which is really close to stock size.

Am I missing something in my 30 second assumptions? I really don't want to buy larger rear bars due to the budget of the project.

Would 21/28, 21/29, or even 30s be better?

I would appreciate any help or advice that someone can give me based on experience. I know that suspension setup can be an art that I have not tried to learn yet. I am looking for knowledge.

Jamie, I put 21(hollow)/26 on Lu's stock 73E and, with the little time I have driving it since the suspension upgrades, I'd say it feels just right for a mostly street driven 911. I think a lot of folks were going with a 21/27 setup, which might be real nice for your lightweight ST replica. Oh...you're is mostly for track...maybe stick with 22/28.

Jamie,
Did you ever find out how to refresh your Koni's? I've got the same shocks but they're also worn out.

Jim, I think I am in the right ball park. I just think a 22 on a lightened front end will not feel balanced. Too much spring for the weight of the car.

Tim, I just put new inserts in them. I mic'd up one of the inserts and it(the shaft) was fine. I did not want to go through the trouble of locating the seals to rebuild them, Koni-NA was not much help. Have you tried to adjust them to increase the damping? Are they leaking? btw, some of the worn out feeling could be the a-arm and spring plate bushings.

Where did you get the inserts? Was it an easy swap? Ive got a tired set of the same ones I think. I called Koni-NA also and they said they would not rebuild them and that I needed inserts.

Any shots of the center gas filler yet?

Thanks!

Jamie,
I had a 72 RS conversion car with 22/28 and it spent lots of time on track and was quite fast. The contemporary track set-up is to go much bigger in back, 30-31mm, I'm sure your set-up will be fine for your intended application.
Phil

My '71 is very well balanced with 22/28 solid bars, Bilstein sports, hard bushings, and stock (!) 16mm sway bars.

Weight is 2230 pounds, but I'm heavier in the front with steel fenders and hood and lighter in the back, 901 trans and mag 2.2S motor.

Tires are 225 front, 245 rear.

Can you post a few update pics here?

Shuie, There are two types of inserts for the early Koni struts. One type, is the "exposed" insert that uses the strut housing to hold the oil. This type has the damping orifice on the bottom of the strut to separate the plunger from the two sides of the bath. The second type is the sealed insert. This is a single unit that bolts into place just like a bilstein or boge.

I don't have pics of the center fill yet. I am still on the fence but have the parts to do it.

No update pics yet. I hope to have the car in finish primer this weekend. No garage and a rainy east coast keeps adding delays to the project.

Jamie

I replaced my exposed setup with some sealed hydraulic units(red) and not the yellow adjustable. They were a cheap find on ebay. I also got nowhere dealing with Koni-NA for parts for the exposed struts.

If you're like me, you will find that over time you can look back and realize that in the last 1000 miles you drove the car, 800 of them were on the track. 23/31 is what you need. Everybody who says 22/28 are plenty stiff and just right, have never tracked a car that was stiffer. HUGE difference. I agree that the smaler setup will give you a good balance as stated above, but the ultimate goal in tracking your car, is to go fast. Faster cars have bigger bars.

Tod (and others who may know), what does the car feel like with big torsion bars and small swaybars?

I've just finished redoing my suspension--new adjustable struts, new bushings, corner balance, alignment, etc.--retaining the 22mm f&r sways, 22mm front tb and 28mm rear tb that wer already on the car. The car doesn't seem too stiff overall and has good motion control, but it's incredibly "crashy" and unstable over diagonal or one-wheel bumps and potholes.

The car also understeers on turn-in. Once set into the turn it feels wonderful, and at higher (street) speeds it has excellent stability and tracking, but it feels like a buckboard in tighter turns.

I'm wondering if downgrading to smaller sways would help, or if I need to go to 21mm front torsion bars, too.

It really depends on what kind of feel you want to have. I know several people that like the car to feel 'loose', so they can throttle steer, or tap the brakes on turn in to move the weight forward. They like the car to have big transition points from l to r turns. I prefer zero movement. I would love to have no suspension, or so stiff it feels like none. What are you after? Keep in mind that understeer is WAY better than oversteer, and 911s are designed to have understeer.

What am I after?

1) A suspension that WORKS (i.e. moves up and down) to follow the road surface.

2) I am very comfortable with transitional or trailing throttle oversteer, but I wouldn't want to do anything so extreme that the rear end would break loose first in steady state cornering.

3) I don't care about ride smoothness, but if the tire leaves the ground every time I hit a mid-corner bump, that can't be good for traction.

I wonder what settings Porsche used for the Targa Florio 911s? Allowing for improvements in tires and shocks, that might be a good place to start.

I have 22/28 on my racecar. It weighs 1850# dry, 2150# wet, has a 3.0L in the back and I think it is sprung very well. I wouldn't be concerened about it.

The shock package will also play an important role in keeping the tires on the ground. Although I have little personal experience, it seems that if the shocks are right, the larger torsion bars are not a significant problem regarding the quality of the ride. See the recent article in "Excellence" magazine.

PS - so those in the know might also specify their shocks and settings along with information about the "size of their bars".

Very important point. Shock valving has as much or more impact on ride quality than torsion bar size. I have 22/29s in my 2450lb '76 and I think the spring rates are fine. I also have the Koni "red" shocks and keep the fronts set at full soft (for the street) and the ride is fine as long as the roads aren't real bad.

Mike

Chris, I know you have lots of glass parts on your lightweight car. Your's was one of the setups I was interested in. I was just concerned that the front would not have enough weight on it for the 22's. I guess that is not the case. What size sways are you running?

Thanks

What is your front toe set at?

I like the 21/30, 22mm sway bars set up with revalved shocks.
IMHO revalved shocks are required with bigger bars.
It's not bad on the street either, my race seat is more punishing than the suspension.

Don't go too soft on your T bars with R rated tires or you may lift a wheel in every turn, smooth or bumpy.:)
http://forums.pelicanparts.com/uploa...1061577802.jpg

I read in Mark Donahue's book that back in the day the early cars ran soft T bars to reduce the high speed over steer. Perhaps with today’s aero packages and superior shocks and tires the old set ups are obsolete?
Racing lap times improve constantly. I would not expect a 30 year old set up to be competitive. Still this has all been done and being done today by hundreds of 911 racers so a lot of development has been completed already.

Here's mine, better, that's not saying much.;)
21/30 T bars, 22 sway bars, revalved shocks.
Perhaps I'll raise the rear/lower the front a touch, add some rebound to the rear shocks.
http://forums.pelicanparts.com/uploa...1061577946.jpg

Front toe = 1/32 total out
Rear toe = 1/16 total in
Camber = 1.2 negative all four corners