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Registered
Join Date: Mar 2011
Posts: 271
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preload / lengh of valve springs
Hello community,
right now I am reassambling my 3,0 heads. In the past there where S cams installed and the red-line was 7600 rpm. Now I will install GE 80 cams. Valve springs are Eibach with titanium cabs. I know Porsche has specs for the valve spring high but I am not sure if the original specs are right for the higher lift of the GE 80 cams. I have a spring rate scale, so I could test each and set the spring-load by using the original shims. Is there a special "force" I should achieve? Like 2 cm spring compression should be 80 kilos or something? How do you guys handle this? -sorry for my bad English! Many thanks in advanced Malte |
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02-11-2013, 10:43 AM
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Registered
Join Date: May 2004
Location: Boulder, Colorado
Posts: 7,275
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I would ask Eibach. I know Aasco's website has spring installed height for their competition springs, so I knew to adjust the shims on mine to 34mm. Maybe Eibach has that information on its website, or has a technical contact?
If you are your own engineer at this level of detail, you would have a target seat pressure, from which the height calculation is easy if you know the rate of the spring package. I'd do that with mathematics, though with a spring compression tester you could cross check that with measurement. With your coil tester you can also verify that at maximum valve lift (including the rocker ratio) you won't have coil bind. The taller the installed height, the less chance of coil bind, though using installed height to avoid bind seems like it is not a good way to go because it requires giving up seat pressure. |
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02-11-2013, 05:59 PM
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Join Date: Mar 2011
Posts: 271
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Hello Walt,
thank you very much for your answer. I will contact Eibach! |
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02-12-2013, 01:12 AM
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Registered
Join Date: Feb 2004
Location: UK
Posts: 2,230
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Malte - Hi
I would aim for 350-375N force at 36mm for the seat force and 1100 to 1150N at 23.5mm. This would be higher loads than standard springs. The spring rate is clearly a straight line between these two points. |
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02-12-2013, 04:27 AM
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Registered
Join Date: Mar 2004
Location: So. Ca.
Posts: 521
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Ultimately a racing spring designed for a specific aplication like a Eibach or Aasco is set 1.25mm from coil bind. Take the measured height from the top of the retainer to the bare head and subtract the lift of the cam and make sure you have clearance from coil bind and that will be your seat pressure with shims
regards |
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02-12-2013, 06:46 AM
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Registered
Join Date: Mar 2011
Posts: 271
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Hi Chris -and racing97,
thank you very much! |
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02-13-2013, 11:44 AM
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