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Old 06-26-2018, 08:20 PM   #18
Tom Broome
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Default Re: Valve Spring Pressure - BBC stocker

Quote:
Originally Posted by nhramnl View Post
Not disagreeing with what you're saying, but if the opening ramp of the intake lobe is too close to "instantly vertical" (like what roller cam guys are using these days) the lifter can actually try to dig into the lobe and create milliseconds of valve train slack (shudder), which can cause things like valve spring surge. Even the roller cam guys admit that there is only so far you can go with "snapping" the valve open and closed.
You answered your own question. You can't open a flat tappet with a specific diameter to the point that the lobe runs off the lifter face radius. That number is somewhat flexible depending on lifter face diameter (remember mushroom lifters?) and base circle diameter.

How far open is the valve at the point of minimal valve clearance? Is it really going to "surge" at that point in the cycle? Could it be a bounce induced from the closing cycle?
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