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Old 05-20-2005, 10:25 AM
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Help! Valve spring seat pressure?

Hi Guys,

Would it be wise to lower the seat presure with 1.8 rocker ratio. Also the valve train will never see high rev like the cam specification ie (cam says valve float 7600rpm regardless 396ci or 496ci)

My motor will never see more than 6200rpm.

Would my motor needs as many seat pressure that the cam card recomends???

This is all after this morning reading the crane cam web site for specs on my card says 132pound at 1.906 and then went to dual spring specs on their site and it says 150pound at 1.900 they are rated at #525pound/inch sooooo it is hard to belive that theirs 18pound difference between 1.900 and 1.906?!!! anyway yesterday I installed all my spring at -+ 1.900 the springs are one year old. Do you guys think I will be ok or I should take some shim off to release some pressure???

Cam is 256 263 at .050 and 618 638 lift
Springs are #99896

Camaro 68 3470 pounds
496ci 10.5:1
Edelbrock oval 290cc
825cfm on AirGap
10.98 at 121mph 1.54 60ft

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Old 05-20-2005, 11:29 AM
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Have the springs been run for a year? If so then they're probably a little weaker than the original specs show. It won'tbe a problem though, engineers account for a bit of that when they spec a spring rate for a particular lobe design.

Have at it and have fun.


Yes, 0.006" can make an 18lb difference.
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Old 05-20-2005, 11:38 AM
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I'll assume you are going from 1.7:1 rocker ratio and stepping up to 1.8:1 rocker ratio.

If that is the case, I would not want to reduce spring pressure. I would at the least go with a new set of springs that will allow more travel for the added lift and now you have added a faster opening action with the 1.8 rockers.

If this was some kind of road motor, I might give you the nod to just install them a little looser. However, since you are racing it, I would probably contact Crane, and get their recommendation for seat pressure and spring rate.

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Old 05-20-2005, 11:43 AM
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coldknock: yes they have been run for a year. If #525pound/inch would it be .006X525=3.15 pound difference??

NAIRB: yes I am going from 1.7 to 1.8. The same spring is good for .680 lift and I have .675 exhaust.

Thanks guys I am a litle bit less paranoid about it.

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