Front Suspension Mods

[Jack Olsen]

Having crashed my 911 at Laguna Seca, I'm looking to make it a little better while putting it back together. I've heard about raising the spindle on Bilstein struts to improve suspension geometry, and (I think) increase the range of negative camber adjustment. I've also read about cutting and extending the front control arms for an improvement in camber adjustability. Does anyone know of shops that do this work, and what the best (and most cost-effective) way to go is? I'm looking for opinion.

When the car is done, it will weigh 2200 pounds, with RSR flaring, 10x12x17 wheels with 275/315 tires. I currently have 21/30 torsion bars with 22/22 swaybars. I'm going to get a Smart Racing rear swaybar, and I'm also interested in people's thoughts on what diameter would be best.

I've modified my strut mounts for -2 degrees camber in front, but I want more.

[campbellcj]

Craig Watkins at Smart Racing Products would be able to help with your spindle-raising as well as figuring out the optimal swaybar sizing and strut/shock valving. Call him, as in my limited experience he is not an email kind of guy.

[CRH911S]

Have you considered contacting Steve Alarcon. He is considered one of the top on this subject.
Clinton

[911nut]

Why not go to coil-overs in front?

[jluetjen]

Chris;
I've dealt with Craig and have found him to be very helpful, not matter what medium I've contacted him on (email, phone, fax).

Alternatively, if you are the type who likes to figure this stuff out on your own, you might want to check out Competition Car Suspension by Alan Staniforth . His book walks you through suspension design, how to measure what you have and how to analyse changes. It also includes everything that you need to build a spreadsheet which you can use to ball park the affects of potential changes to the car. At the end of the day, if you've developed the understanding yourself (as opposed to depending on someone who isn't at the track with you), you will find yourself with a much better understanding of the car and how to dial it in on race weekends.

BTW --

Another of Staniforths books; The Race and Rally Car Source Book is another invaluable resource for understanding your race car and how to make it happy.

[jpachard]

Jack, Something you might want to consider is welding in a rollcage. I only bring this up because the older chassis are fairly flexible, especially with the power you are putting out, plus it makes the wife feel better( ask me how I know!!). I am in the process of putting one in my car which I am copying the factory Cup car one from a 964 Cup car. As far as the front suspension goes, I would go with and ERP coil over setup, if money is no option

Best of luck, James

[stlrj]

These guys could modify your front end for all the camber you can handle: http://racersgroup.com/customfab.html

Cheers,

Joe

[dtw]

Jack,
I don't think modifying your a-arms is what you're looking for. How about adjustable links? Check out the suspension on this car:

(Lots of other good "ideas" in these pics, too)

http://www.pelicanparts.com/MotorCity/WintersRS/garage/Photos/speed4.jpg
http://www.pelicanparts.com/MotorCity/WintersRS/garage/Photos/speed5.jpg
http://www.pelicanparts.com/MotorCity/WintersRS/garage/Photos/speed12.jpg
http://www.pelicanparts.com/MotorCity/WintersRS/garage/Photos/speed13.jpg
http://www.pelicanparts.com/MotorCity/WintersRS/garage/Photos/speed14.jpg

[addictionMS]

Jack,

Here is what I have, (F/R)

23/31 tubular torsion bars
SRP 31/27 sway bars
Bilstien shocks 930Frront/ re-valved by SRP rear
Camber boxes and plates

this is a real solid set up, it is very close to what Rich at SRP is running and setting new lap records in PCA with.

Not very streetable,

I would also suggest the full cage, and fuel cell, safety first speed second, is always my motto

Jim

[Superman]

I have no idea what's best for you, and you seem to have some names of some folks who can help you a great deal. I'm going to add another name. Greg Fordahl's skills are getting quite a bit of attention these days. Excellence called him the wizard of Porsche suspension setup, in a story a few months ago about the 24 Hours of Daytona race. He seems to be travelling the country now setting up winning suspensions. He and his wife won the mens and womens autocross titles, respectively, at the Roundup in Boise this year...pictures in Panorama.

From what I know about Greg locally, I have every reason to suspect his reputation is well deserved. I won't bore you with the various stories of local folks whose times have been substantially reduced by his Midas Touch. His website:

http://www.fordahlmotorsports.com/

If you have the inclination, I believe it would be worth your time to call or write him. For example, the Daytona team that called upon him reported that the car's times were shaved by 2 seconds after only one trip onto the alignment rack under his direction. That car, a privateer, took either first or second (my memory has faded). The Excellence article is embarrassingly lauditory.

[jluetjen]

Chris;
To expand on James' thought, keep in mind that all chassis flex. The question is : How much? Mark Donahue mentions in his book "The Unfair Advantage" that the 911's that they worked on flexed at a rate 2000 ft-lbs/degree, which he considered plenty stiff. Keep in mind what this means to your alignment. For every 2000 ft-lbs of torque you apply to the chassis, it will twist 1 degree. Imagaine that you have 500 lb springs on the front and that they are about 2 feet from the car's centerline. If you corner such that you compress the outside spring by 1 inch, this is 500 lbs at 2 feet or 2000 ft-lbs or torque. Add on a stiff roll bar and you most likely have even more torque being applied to the frame. Now your rear suspension is rolled 1+ degrees further then your front. This additional roll at the rear basically dilutes the affects of your sway bars. As a rule of thumb I seen that your chassis stiffness should be about 20x stiffer then your spring stiffness if you want to keep it's contribution to the cars total movement to less then 5%.

A very popular and effective way of exploring frame designs is by making simple balsa wook models and then applying weights to twist them. You can also trying using some FEA Shareware from Grape to try investigating some options. You might be surprised by how good or bad some popular designs are.

The other thing to keep in mind is that everywhere that you look or listen, you'll see an interesting way of doing something. You'll find this neat design/wing/feature or that different way of doing something. The one thing that I've always read/heard from the great designers is that you will rarely gain much by just copying since every racecar application is different (unless every effort has been made to copy exactly the entire package -- say the different cars on the same F1 team). So always be sure to ask the following questions as you are looking at options:

1) What was the designer trying to accomplish?
2) Why would this work?
3) What can you learn from it which might apply to your package?
4) (Difficult for the amateur: ) How do you test it?

[campbellcj]

I don't pretend to understand (er, remember?) all the physics involved, but the difference in chassis stiffness and torsional rigidity was immediately noticeable and non-trivial when the welded 8-pt cage was installed in my 914. And this is an interior cage only, no thru-firewall or pickup point bracing.

Also, FWIW Steve Alarcon is selling some Koni fronts with race-valve inserts, de-cambered and raised spindles. I contemplated them but ended up using some Bilsteins I had in the garage.

[Bill Verburg]

The ERP front suspension is very adjustable(for the big rubber up front you will want all of the adjustability you can get), in particular the camber pattern needs to be flattened. A diagram:


An installed pic;


Note the coil overs and tierod kit. These are available at Smart Racing or Autometrics

In addition I second(or third or whatever) the suggestion to talk it over w/ Steve Alarcon @ Johnson Alignment

It sounds like you are headed for an all out race car(which may or may not see street use), if this is the case a full cage tied into the suspension pickups is indicated.

[addictionMS]

Bill,

your car is way too nice to drive.

Jim

[Bill Verburg]

Not my car

[surflvr911sc]

Jack, I don’t know if it’s what you’re looking for or if you could even use it but I have a Bilstien left strut assembly that I took off my car. It was “modified” (probably by a pot hole) to get –3 degrees camber. If you think you could use it for experimentation, I would be happy to donate it to the Return of BB fund.

Missed you Sunday at Big Bear Run II. We had a great time with great people.

[pbs911]

Why do I have the feeling Jack is going to be at Willow Springs on December 12th, wider, faster and lighter than before?