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Old 07-05-2006, 05:10 AM
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toad490 toad490 is offline
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Default Valve Spring Pressure And Spring Rate Questions

Hi, using the spring rate how do I figure out what the pressure would be at my cams lift, .688? The seat pressure is 275 lbs, with of spring rate of 594 lb per 1.00". My math skills have let me down.

How close to the makers recomendation is "close enough"? I've got a Straightline solid roller, it calls for 275 lbs at the seat and 600 lbs on the nose.

How much can shims raise the pressure of a spring?
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Old 07-05-2006, 06:42 AM
sanborn sanborn is offline
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I assume the camshaft gross lift is .688". If I were to calculate this, I would deduct the valve lash(for example, .022") to get a net lift at the valve of .666". Multiply the net lift(.666") times the spring rate of 594 lbs. per inch for a spring pressure gain of 395 lbs. This plus the initial seat pressure of 275 lbs. yields a total pressure of 670 lbs. across the nose.

Spring shims raise pressure based on the same general math. For example, a .030" shim on a 594/inch spring would raise pressure by 17.8 lbs.

Be careful when calculating theoretical ratios, rockers are not always exactly 1.5 as specified, you sometimes get other losses as well such as pushrod angle losses, pushrod flex, valve train "slop", etc. In the case of W2 heads, pushrod angle losses are major!
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Old 07-07-2006, 12:19 AM
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Thanks Sanborn, that helps alot.
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