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Old 01-21-2004, 03:00 PM
84 Z28 Convertible
 
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Installed Spring Height

Do any know the formula for figuring the installed height of springs. What I want to do is set my spring up to be 130-135 seat and 330-335 open, but what height would give me the steup is the question. Hopefully someone will provide a wonderful links that will break it down to the lowest level.
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Old 01-21-2004, 03:26 PM
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You have to know the spring rate (# per inch) number before you can figure it. You can't without it.

Formula
Seat Pressure
Free length - Install Height = Deflection x Spring rate = Seat

Open Pressure
(Cam lift -Install Height) -Free Length =Deflection x Rate = Open

Chris
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Old 01-21-2004, 06:44 PM
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Lets try this:
Here is the specs on the spring part#8033 upgrade that AFR puts on there heads for Flat tappet Solid Cam, so I want to make sure they will work and NOT wipe a lobe.
410 per inch
140 seat @ 1.930
365 open @1.380

I'm really trying to understand this spring pressure, open, and seat. So that I can check for the correct install height on my heads.
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Old 01-21-2004, 06:55 PM
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You already have all the information.
Right there in your spring specs.

140 + (.55 x 410 lbs) = 365lbs at 1.380

every .010 change in installed height equals about 4 lbs
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Old 01-21-2004, 07:05 PM
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This is my method:

Put the spring in a vise, compress it to coil bind. measure it.

Take the measurement of coil bind, add in the lift of the cam, an additional .080 -.100 for safety margin and you will end up with "X"

1.930 will need to be equal or more than this "X" number.

"X" will be your MINIMUM installed height.

Install the valves, measure the height (where the spring would be) with a retainer and locks installed. You will end up with "Y"

This number must be at least 1.930

"X" cannot be less than "Y" Normally "Y" will be greater.

The installed height of the spring must be between "X" and "Y" The best way is measure the spring tension. If you do not have the tool you can use the spring specs. Shim as required.

You must also measure from the top of the guide to the lowest part of the retainer without the spring installed. This dimension must be greater than the lift of the cam. Otherwise the retainer will smack the guide.

Clear as mud?

I usually write the "X" dimension on the head next to each valve.

In your case 1.930 needs to be between "X" and "Y"

Last edited by Infomaniac; 01-21-2004 at 07:14 PM.
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Old 01-21-2004, 08:57 PM
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Info, you need a Rimac, your method is hurting my head!!!!

Chris
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