Valve Spring Pressure - BBC stocker

[nhramnl]

Originally Posted by Tom Broome

Hard to loft an intake valve on opening, it's only moved the tappet .100 or so. Now over the nose....okay, but the piston is long gone by that time. Possibly a big bounce off seat? Pushrods might change things
.

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.

[ghost]

Do you run with Hydrolic lifter????

How many lash you have between rochers to valves 0 or 1/4 lap

[Chipper Chapman]

Spoke to COMP today, they are claiming that the lobe is so aggressive I need to get a different spring that is going to allow me the same open pressure, but within .050” of coil bind. He claimed that the spring is most likely doing the hokey pokey since it’s about .400” from coil bind, and not designed to work there. I thought pressure was pressure, but is this something that could actually be going on and therefore causing such an issue?

[Rob Wright]

Originally Posted by Tom Broome

Possibly a big bounce off seat? .

Probably. Horribly upset combinations can/do bounce that much. Sometimes it gets better with less spring pressure. Maybe not with this one, but it's not unusual.

[Hacksaw]

Originally Posted by Chipper Chapman

Spoke to COMP today, they are claiming that the lobe is so aggressive I need to get a different spring that is going to allow me the same open pressure, but within .050” of coil bind. He claimed that the spring is most likely doing the hokey pokey since it’s about .400” from coil bind, and not designed to work there. I thought pressure was pressure, but is this something that could actually be going on and therefore causing such an issue?

I think the info from Comp is accurate, but I think looking for another cam and matching springs is in order.

[Alan Roehrich]

What valves and pushrods are you using?

[Chipper Chapman]

Originally Posted by Alan Roehrich

What valves and pushrods are you using?

Ferrea Competition valves (not the hollow ones as I was told they are illegal) and trend 3/8x.120 wall pushrods

[Tom Broome]

Originally Posted by nhramnl

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?

[Tom Broome]

Originally Posted by Rob Wright

Probably. Horribly upset combinations can/do bounce that much. Sometimes it gets better with less spring pressure. Maybe not with this one, but it's not unusual.

Pushrods are a spring also. The rate gets altered through diameter and wall thickness.

[Tom Broome]

Originally Posted by Chipper Chapman

Spoke to COMP today, they are claiming that the lobe is so aggressive I need to get a different spring that is going to allow me the same open pressure, but within .050” of coil bind. He claimed that the spring is most likely doing the hokey pokey since it’s about .400” from coil bind, and not designed to work there. I thought pressure was pressure, but is this something that could actually be going on and therefore causing such an issue?

They own a Spintron, not me, but inducing spring clash is possibly a solution, probably not the most elegant....but a solution.