Spring rate advice Options

[BlueRidge914]

I’d be grateful for some spring rate advice for my vintage race 914.
It’s a narrow body 2L six, 205/50 tires all around. Front torsion bars with adjustable sway bar. Rear is Bilstein Sports with adjustable spring perches, and a fixed sway bar.
My personal preference leans to a relatively softer spring all around.
Any recommendations for both torsion bar size and rear spring rate?
Thanks!
Gavin
VARAC #58

[brant]

What diameter front torsion springs do you have?

We run 911 front torsions which are bigger than -4

I currently run 21mm hollow front with 275lb rear

Brant

[BlueRidge914]

It was more than twenty years ago since I installed the front T-bars and rear springs (shocks and struts have been replaced), and I can’t recall what rates they were Brant. I think the springs are 250. I’d like to go hollow and move from 2.5” to 2.25” rear springs, no helpers as the rear sway bar keeps the back end flat.
Your combination sounds good. Still on the soft side that I prefer relative to current practice of going stiffer .
Thanks Brant

[slivel]

I believe that you get performance gains by going as stiff as possible but not so stiff that you are bouncing over rough pavement. Stiffer helps to prevent front end dive under braking and rear end squat under acceleration while keeping the balance close to what the chassis has statically.

The tracks that I frequented were pretty smooth and I did not feel like changing out my suspension from track to track. Final race configuration for my car had 450 front and 400 rear. The car and driver are now retired and I have softened the suspension by using stacked springs giving me a progressive rate.

For what it's worth, I'll attach my spec sheet and a suspension worksheet.
 1975_Porsche_914rev16.pdf ( 69.19k ) Number of downloads: 60

 Suspension_for_914_world.pdf ( 200.22k ) Number of downloads: 46

[yeahmag]

What type of racing? What tires? Do you have an LSD?

[BlueRidge914]

Tires are 205/50x15 all around, treaded - no slicks, as per vintage race rules.
WaveTrac in the gearbox.
Tracks are mostly fast and smooth (CTMP Mosport home track), but also some shorter, bumpier tracks.
I’m not unhappy with the car’s handling, but since it’s all I’ve raced for so many years, I may not know what I’m missing. But it’s time for a refresh anyway.
I’m not aiming for big changes like Vons and 935 style fronts, but what works for spring rates on a generally original suspension setup.
Thank you!

[campbellcj]

I believe that you get performance gains by going as stiff as possible but not so stiff that you are bouncing over rough pavement. Stiffer helps to prevent front end dive under braking and rear end squat under acceleration while keeping the balance close to what the chassis has statically.

The tracks that I frequented were pretty smooth and I did not feel like changing out my suspension from track to track. Final race configuration for my car had 450 front and 400 rear.

Mine was set up for primarily track use along similar principles and IIRC has 22mm hollow 911 t-bars and 350 rears (may be 300 or 325). Very flat and stable on track (or canyons), but nearly intolerable for street use.

[BlueRidge914]

That is great advice - thanks. And sort of what I was thinking.
One more race, then probably 22mm hollow bars and 300lb rear springs (keeping the rear sway bar) over winter. I’ve raced this car 25 years, and I don’t think big changes would make it any more fun for me.
Gavin

[yeahmag]

I think what Chris says is a good place to start. Treaded tires, even race tires will produce less grip than slicks. I'm running A7's, 450's, a stock rear sway bar, and custom Penske shocks on mine for autocross and I like it. Might try to lower the spring rate a bit to something like 350-400 now that the bar is in and the shocks actually do their job.