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What's the rule of thumb for using double valve springs instead of singles?

I'm planning to install a new cam in my 351C that has 12.8 to 1 comp pistons with closed chamber heads. It's an engine I used to use in a drag car but made a mistake when I broke-in the original cam with solid lifters and roller rockers.

Denk

 

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Use the springs recommended for the cam.
 

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On 4V 351C motors I dont always go with the cams spring specks. It because they are big heavy valves and aftermarket cam MFGS of give seat and open specks that are ok for little lighter weight valves. I have also converted to behive / conical springs in apps were possible as they have heaveryer values that many dual springs open and closed but much lighter in weight and have a much less of tendancy to go into harmonics.
They are also progressive rate enabling them to open and close quicker.
Depends on your cam some hyd , solid , solid roller.
 

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As far as doubles or singles, use what's recommended unless you know more than they do about your application. That also often means using different springs for engine break-in than the ones to be run. My last FT performance cam required the cam to be broken-in with only the outer springs as per the manufacturer recommendations.

This technique is popular these days, as is using the soft stock springs for cam break-in if they don't coil-bind. They are strong enough to break the cam in at the proper low rpms with far less chance of wiping a lobe. Just don't rev it. After cam break-in, swap the springs and have fun.

David
 
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