swb suspension setup opinions needed

[gestalt1]

hi, i'm getting ready to send out my bilstein struts/shocks to be re-valved and i want to give bilstein the right info so the valving is correct. basically i'm building a 911r clone on a 68 912 chassis. i am converting to the 911 engine the car will weigh about 1800lbs. i did some research and found that there is a 6-7 mm difference form the front to rear torsion sizes on factory setups and race cars are more like 8-9mm. i'm planning to run 21mm front and 30mm rear solid torsions and a 19mm front sway with no rear sway. i am hopeing that the torsions will provide good control and the sway can ba a tuning aid to adjust the front to rear understeer/oversteer balance. i realize this is a little odd setup and it may not work well. if i have the bilstiens valved for these specs will they be ok if i switch to a more conventional setup? (by conventional i'm thinking 21mm front, 29 rear with 19mm front and rear sways).

btw - this will be a barely street legal race car that will get most miles on the track and driving to and from the track.

thanks!

[304065]

No, the valving of the shocks is specific to the torsion bar size. Remember that the spring rate increases with the fourth power of the diameter, so going 21/30 vs 21/29 will make a difference. Remember, the relationship between sizes is not linear, so a 6-7mm difference at one level is not the same as the same difference at a different level.

Why not stick with a proven combination like 22/28? That will make it easier for Bilstein to match. Also, remember that the SWB springplate is shorter than the LWB-- as such, you will realize a higher wheel rate with the SWB than with the LWB, something to take into consideration if you go bigger in the rear.

With fixed valving it's tough to accomodate changes unless you want to carry around a whole steamer trunk full of shocks (Carroll Smith).

I used to have 22/28 on my LWB 1971, then went to 23/31 which I like a whole lot better. Truth is it is impossible to get enough spring rate in the rear with torsion bars, which is why the factory went with coils in the early 1970s on their race cars-- that and adjustability.

[gestalt1]

thanks for the advice John, what do think about running just a front sway? it seems that most vintage race swb cars run the 18mm sways front and rear with the biggest torsions available.

[304065]

If you want to vintage race I would convert to a LWB front end if the rules allow, use 23/31 and use a Smart Racing 31mm front bar and a 27mm rear bar.

[V12man]

I have a '67 running 23/33 torsions and 23mm SMART sways front and rear - shocks valved to match the torsion bars. I did run it with the front sway bar only for a period, without issues, but marginally less tune able than with both front and rear.

Installing the rear bar was a real pain as the mounts have to be spaced inwards on the swb, and I only noticed that after installing one side - oops

Surprisingly, it is not as hard a ride as I thought it would be, and would reccomend the setup to anyone who uses their swb car mostly on the track, without going to the expense of a coil over setup.

My setup was reccomended and sourced from Steve Weiner, who is both a porsche scholar and a gentleman.