A friend gave me some rear springs for the 914, are these aftermarket and if so, best guess to rate?

Silver stripe with a few coils painted green.

Stock is 100 pounds correct?

Thanks.
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If they are 140 they would say SP140 on them. Only the factory put paint marks on the springs.
The SP140 springs are from Weltmeister / Automotion.

Thanks, I guess I can break out the calipers and measure the spring diameter and compare to what I have.

you can also very crudely measure the spring rate by putting them on a scale, compressing them 1" and see what the scale reads (I used a shop press to do this)

The paint marks versus spring rate is in the manual. I will try to find it later.

Once I set up on press I checked a few sets I had,
100's,140's even 180!

Stock is less than that, supposedly 60-70 pounds. In the old days Weltmeister/Automotion offered replacement springs rated at 100, 140 and 180 pounds. I replaced my originals springs with their 100 pound springs on Koni red shocks and it raised the rear noticeably.

Automotion, new owners, still has these:

https://www.automotion.com/1974+porsche+914...nd-chassis.html

Click to view attachment

Okay. Now we need to convert kp to pounds per inch.

excellent information, Steve

I tried the google conversions for two green dots and it came up with 300 lbs. I know that’s not right. Maybe you don’t times the psi of the whole spring length?
Curious though, unless your a concours weenie, most people either install the 100 LB Weltmeister springs for stock front torsion bars or the 140 LB versions versus 40 year old saggy stock springs. The 100 and 140 welt springs are stock length and very low cost. The 180’s are shorter, so most people buy coil overs for this spring rate or higher, since they have adjustable collars. I am running 150 coilovers from Rebel Racing with my 3.2 and 915 gear box.

Thanks Steve,

Those springs are reasonably priced, I know I want the car at least 1" to 1.5" lower than it currently is so I might go with the adjustable coilover option that I can tweak.

....ouch, slightly bigger front torsion bars are pricey!

The Factory spring spec here can not be converted to the typical lbs per inch spring rate we are used to, without additional information.

The Factory spec is force at a given length, as in compress the spring to the length in the spec and you should get the force listed in the spec. So for springs with 1 green dot if you compress to 239 mm (almost 9 1/2 inches) you should get the 220 - 227 kp of force, about 485 - 500 lbs.

In the typical lbs/inch spring rate there is no specificied length at which we measure the rate, we just compress the spring until we have a stable reading and note the reading. Then we compress an additional inch and note the increase in the reading to get our lbs/inch spring rate. I used to crank the spring down until I had an even number of puond, such as 100 pounds of pressure. Back then I remebered how many thread per inch the spring scale had and I could just crank it down an addition 11 turns (or what ever the number was) and take my reading again. if it was now 240 pound then the rate was 140 pound per inch. For lenear rate springs the pressure increase as teh spring is compressed each inch should be the same until coils start to contact each other and limit their travel.

If you are progressive springs and not measuring springs with a linear rate then you need to crank them down to the pressure range your spring are going to be while installed. The rear springs of a 914 carry somewhere around 550 pounds or so depending on the total weight and weight distribution. So for a progressive spring I would crank down to 500 lbs and then another inch and note the pressure, then another inch and note the pressure and then anther inch and note the pressure. For progressive springs change in pressure as the spring is compressed will be higher. Maybe the first inch added 100 pounds of pressure and teh second inch added 115 pound of pressure and the thrird inch added 140 pounds of pressure. You build a profile of the spring rate for the spring.

Jim

Yeah, the big unknown is exactly what L1 is. Is that the overall length of the spring? Is it some reference point on the spring that isn't the very end? Is it something else?

--DD