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Posted by: ChrisReale Mar 31 2003, 06:47 PM

What does a stock sized torsion bar equal in spring weight? I am guessing that the stock bars are close to equal to the stock rear spring weight, which is somewhere between 60 and 100lbs, right? I have also read that 21mm bars are close to 175# in spring weight. So, what would 22mm torsions equal? 23mm...?

Posted by: Mueller Mar 31 2003, 06:52 PM

You need to take a few measurements first

http://www.stockcarproducts.com/pstech6.htm

Posted by: ChrisReale Mar 31 2003, 07:02 PM

math.... :toilet:

Posted by: mskala Mar 31 2003, 07:08 PM

Math's been done. Stole this from 911 list a billion years ago.
> A fellow Rennlister, Joe Winn, measured torsion bars he had for sale,
> and the following is for the FRONT bar:
> -length of 611 mm ( or ~24" )
> -spline length at each end of about 1".....this makes for an
> "effective" length of 22" , assuming full length spline engagement as
> installed. Also, I'm using a lever arm measurement of 12"...the distance
from
> the torsion bar centerline, to the brake caliper centerline. With this , I
> come up with:
> SIZE ( mm) SPRING RATE ( Lb/in)
> 18.8 110
> 21 173
> 22 210
> 23 250
> 24 296
> 25 350

Mark S.
'70 914-6

Posted by: TimT Mar 31 2003, 07:09 PM

Check http://instant-g.com/Data/911CoilConv.html out

Posted by: Jeroen Apr 1 2003, 05:07 AM

Ok, so which of these two is correct?

cheers,

Jeroen

Posted by: mskala Apr 1 2003, 07:26 AM

Check Mueller's calculator. If the arm length is really 12"
(not going to check this minute) then it returns the same
numbers as my copied mail. On TimT's link, the page
doesn't even work right, and the numbers are very
suspicious.
Mark S.
'70 914-6

Posted by: TimT Apr 1 2003, 04:08 PM

The link I tossed up isfrom Steve Timmins home page, he does loads of 3.6 swaps in 911's and he is a physics teacher at the University of Delaware. I think he is involved in the "Vehicle Dynamics& Powertrain Theory" program at UD, I met the guy once at Watking Glen and he seemed to know his stuff.

One glaring problem with the stock car product calculator is that no provision is made for torsional modulus of the steel. It appears an assumed torsional modulus has been incorporated into the applet. Porsche may use a different modulus steel in there torsion bars than was used in the applet.

Another thing to consideris do a pair of springs have the same spring rate?

I bought Hypercoil #550's for the rear of my 911, onespring was actually 553 the other 559... Its a small difference, and the difference vanishes when you corner balance the car.

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