Just found out an interesting bit of info thanks to the spintron. First a little background, My brother and I were running a 353ci chevy motor in B/ED (comp eliminator) a few years back and it had dropped #8 intake valve 3 times in 12 passes. Due to lack of funds and life getting in the way it sat dorment untill our friend Dick needed a motor for his new front motor creation. We lent him the motor with the premise if you can fix it enjoy! He hauled the junk over to Jesel's place to try and get an answer and here is what he found, 1. the springs were too far from coil bind @.200in. They changed the install height so only .030in to cb was acheived 2. Running such a large cam makes the core prone to twist and with out running a cam driven oil pump the back of the cam whips the lifter way off the lobe. With .200in to cb the valve would bounce hard enough to snap the lock or retainer. Setting the cb to .030in helps control the valve at 10,200rpm. All assembled and very conservative on the tune it pulled 798hp on the first pull, 837hp on the second pull. Not bad for a C/D its going in but probably not very competitive either. Terry @ Jesel's said the intake was all wrong, and it should end up in the 850hp range.

Kevin

 

Your springs were originally set up to .200 coil bind and now they're at .030. .170" more spring travel is a lot of spring pressure lost. No wonder the valves floated.

If the springs were rated at 700 lbs/in that would mean a loss of 119 pounds of spring pressure when open. Since the installed height was also changed, the closed seat pressure must have been very low also. That's what would have caused the valve to float (bounce on the seat).

 

If the springs were rated at 700 lbs/in that would mean a loss of 119 pounds of spring pressure when open. Since the installed height was also changed, the closed seat pressure must have been very low also. That's what would have caused the valve to float (bounce on the seat).
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Could be that the spring pressure was too low to rev to 10,200.....maybe it would of lived longer crossing the line @98-9,900.
Im not sure by todays standards but fresh springs would check 320lbs on the seat and get shimed @ 290. Its been about six years since we ran this motor and I know valve spring technology has come a long way.



Your springs were originally set up to .200 coil bind and now they're at .030. .170" more spring travel is a lot of spring pressure lost. No wonder the valves floated.
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The reason for being so far from cb comes from the use of a pro stock style spring. At coil bind it has traveled 1 inch but we were only lifting the valve .801 intake,.792 exhaust.