Oh this is all too confusing......
The lube a lobes? type 1 I presume?
the only way to know if any combo works is to put 30-40k miles on it.. a lot of combo's will work for 5000........ I need it to be super reliable, I dont want the cam and lifters to eat each other...
Are the ceramic lifters stil off the menu????
solid lifters on hydraulic cams??
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fastback
- Posts: 1670
- Joined: Wed Sep 12, 2001 12:01 am
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tencentlife
- Posts: 424
- Joined: Tue Apr 25, 2006 8:13 am
Re:
Just revisiting this as the question was left hanging. Piledriver was correct above, the essential difference between a hydro- vs. a plain-grind lobe is the plain-grind must have low initial ramps to take up the valvetrain lash before actually lifting the valve. That is why your plain-grind cam card specifies the rocker ratio and the required lash setting, those things are calculated to work with the height of the lash take-up on the cam lobe. After that there is a transitional area from a low rate of lift to the maximum rate, and in this area both types of lobe are basically alike.Piledriver wrote:
Solids have GRADUAL ramps to take up the lash smoothly.
Pile's explanation made good sense but to prove it to my own satisfaction I started plotting out the lift-to-rotation of all the cams I had and this is what comes out in the plots. I did this a few years ago but never got round to sharing this info for anyone not yet clear on the concept.
At the time this thread started, I had adopted much of my conception of hydro lifter operation from Ratwell's article, where he talks about an inertial reaction of the check ball as the lifter begins to move from riding the base circle being necessary for admitting oil, but either I misinterpreted his writings, or his explanation is overly-complex. In reality the hydro lifter constantly takes up any available lash in the valvetrain simply by virtue of oil pressure inside causing it to expand, the oil pressure alone is able to push the ball check valve open. This process is aided by the expansion spring that seeks to lift the plunger in the bore of the lifter body. Once the cam begins to move the lifter, the valvespring counterpressure on the plunger forces the ball valve to seal more firmly on its seat and from that point on the lifter acts as a solid, with one minor difference: when loaded, oil bleeds constantly up the minute tolerance between the plunger and the main bore. It is this controlled bleed-off that allows the lifter to gradually lose effective length, otherwise once it extended to the length where it eliminated all lash it could not become shorter to accomodate contraction of the engine as it cools, and then the lifters would hold all the valves off their seats, probably making it impossible to cold-start the engine.
The total force exerted inside the lifter when it is off the cam lobe by the plunger spring and the oil pressure making the lifter expand is a small fraction of what would be required to lift the valve, that calculation can be done in seconds in your head, so the notion that hydro lifters can "pump up" with excessive oil pressure and hold their valve open is a myth, with two exceptions:
When a valve floats, there is momentary lash in the valvetrain which the lifter will take up bit by bit. If float is at all chronic that lifter can end up holding the valve off the seat when closed. It should self-correct by bleed-down if the float condition is intermittent, but if any valve spring fails to keep the lifter tracking the cam constantly in normal use misfires and burnt valves will probably result.
The other instance is unusual in that it can only occur if there is an error in the cam grinding process that leaves a dip in the cam lobe's base circle. Rocky and I both learned about this the hard way when a batch of CB cams had this defect, a measurable reduction in the base circle radius we measured as between .003" and .008" on only one lobe of these cams (CB did become aware of it, replaced unused cams, and we haven't seen the flaw since). The lifter would drop into the dip in the base circle on each revolution, and bit by bit expand to fill the resulting lash, and from then on it would be holding the valve off the seat while it was riding the remainder of the base circle that was at the correct radius.
The only negative effect I have been able to see from using hydro lifters on a plain cam is that they open the valve a bit earlier and allow it to seal shut a bit later since the lash take-up ramps will actually open the valve rather than merely taking up slack. In my measurements this results in about 2"Hg. lowered vacuum at idle, a fairly minor change. There's no reason it would result in any longterm harm to the lifter, though, because if anything it is being handled more gently.
But as Pile said earlier, using plain lifters on a hydro-grind cam could possibly cause harm to valvetrain components eventually, because without that gentle lash take-up, they would be hammering open and shut, and long term that additional stress may cause something to fail (most likely the valve head separating from the stem below the weld, but that's just my own speculation).
There is also always controversy over heavier-grade oil being preferable to lighter for good hydro operation (controversial because it involves oil, I guess!), and on this I come down firmly on the lighter side. Heavier oil should lessen the instance and severity of start-up lifter clatter by lowering the bleed-down rate when the engine is at rest, because two or more lifters will be parked on a lobe no matter in which position the crank comes to a stop. But lighter oil fills soft lifters much sooner when there is start-up clatter, and moves thru the lifter at a higher rate during normal operation, allowing the lifter to respond more quickly to dimensional changes as the engine temp changes, both up and down. And a better flow rate means a cleaner lifter as far as I can see.