Stock evo lifters always where a bit weak, swap them out to a good set of S&S, Vulcan, or another decent brand ( several more I can't remember the names of ) and the issues go away and you keep a nice quiet motor. Unless you go to a cam specifically for solid lifters the lobe design for the hyd. cams will beat the **** out of the lifter rollers and the valve train. The lobe ramp design between the 2 are very different.

 

 

Years back we put a shovelhead engine in a hard mounted test stand with a dial indicator on each rocker box, turned the fan on and fired it up, set the RPM to 1500 and let it run for several minutes. Keep in mind this is a cast iron cylinder with the alum head configuration with no through bolts like the evos and later. Both grew to .070"+ in height. That's a lot of lift loss considered, always been curious what the all alum. engines would do in the same test. Suspect it'd be close or more.

 

Yes, just my opinion. As I've never had or seen in my experience a lifter pump up and cause damage (i'n not saying that it can't or doesn't happen), even on the dyno. All the lifter failures that i have seen have been either collapsed or oil pressure issues, galling and sliding rollers, roller failures, but no pump up.
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The basic operating principle behind hydraulic camshafts is truly old school technology. In 1910, a French car builder near Le Mans, France named Amedee Bollee invented the first self-adjusting valve tappets. Bollee’s two-piece tappets consisted of an upper and lower piston held slightly apart by a small spring. A port in the side of the lifter bore allowed oil to enter the cavity between the two pistons.Oil pressure pushed the upper piston up to remove slack between the tappet and valve (this was a flathead engine where the tappets push up directly against the inverted valves). There was no danger of oil pressure pushing the valve open because the pressure exerted by the valve spring holding the valve shut was far greater than the oil pressure inside the tappet. When the cam lobe raised the tappet, a one-way ball valve in the oil port prevented the oil between the pistons from leaking out. The oil trapped between the two pistons was incompressible, so the tappet acted like a solid member to push the valve open.
In a modern hydraulic lifter, a hardened steel push rod cup sits on top of a plunger mounted inside the hollow lifter body. A lock ring in the top of the lifter holds the assembly together. Under the plunger is a spring that holds the plunger up so oil can fill the cavity between the plunger and lifter body. A one-way check valve in the bottom of the plunger allows oil to enter the plunger cavity but traps the oil inside when the lifter moves up. This prevents the lifter from collapsing, which would not allow it to open the valve fully.The clearance between the plunger and lifter body is extremely tight, typically 0.0002? or less. This is done to limit oil loss from inside the lifter (called the “bleed down” rate) when the valve opens and closes. A small amount of leakage (bleed down) must be allowed with each valve cycle so the lifter can readjust itself to maintain zero valve lash.Valvetrain clearances change with temperature as the engine heats up and cools down, so the hydraulic lifters have to constantly compensate for thermal expansion in the block, heads, pushrods, valves and other valvetrain components. If this were not done, the lifters might retain too much oil, pump up and overextend themselves, preventing the valves from fully closing. This, in turn, can cause valve float, a loss of compression, misfire, and possible valve damage if a valve remains open long enough to hit a piston.
The very feature that allows hydraulic lifters to self-adjust and maintain zero lash can also work against the lifters at higher engine speeds. As engine rpm increases, the bleed down rate inside the lifters may be too great. There may not be enough time to refill with oil between each valve cycle, causing the lifter to collapse. Or, if the bleed down rate is too low and the lifters retain too much oil, they can pump up and overextend the valves. Either way, you can end up with valve float, misfiring and loss of power.
The rev limit for a typical set of stock hydraulic lifters is usually around 6,200 to 6,500 rpm. If you want to rev the engine higher than this, you either need solid lifters or modified performance lifters that can safely handle higher rpms without pumping up or collapsing. The bleed-down rate of a hydraulic lifter can be varied by changing the internal clearances between the plunger and lifter body for other reasons too. Some aftermarket hydraulic lifters designed for street use have a higher bleed down rate that effectively reduces camshaft duration by 6 to 10 degrees and valve lift .020 to .030? at low rpm for increased intake vacuum and throttle response. At higher rpms, the higher bleed down rate has less of an effect allowing normal camshaft duration and lift.Hydraulic lifters that have an “anti-pump up” design are made with tighter internal clearances and/or special valving to reduce bleed down. Anti-pump up lifters allow higher engine speeds and are a good choice for a dual-purpose street/strip engine. One supplier of such lifters says their anti-pump up lifters can handle engine speeds up to 7,500 rpm with no valve float, and can even be used with many camshafts that are designed for solid lifters.
The lobes on hydraulic cams are ground slightly differently than those on solid lifter cams to better accommodate the way in which hydraulic lifters operate. The opening rates on a hydraulic grind may be somewhat higher to overcome the slight bleed down that occurs inside the lifter, and the closing ramp may be more gradual for quieter operation of the valvetrain. Can you use solid lifters on a hydraulic cam, or hydraulic lifters on a solid cam? Anything is possible, and the results will vary depending on the grind and application. Solid lifters cannot be run with zero lash, so they usually require anywhere from .004? to as much as .015? of lash depending on the grind and application. With some cam profiles, the lifters may become extremely noisy at higher engine temperatures and speeds. Thermal expansion will be greater on engines with aluminum heads than those with cast iron heads, so the “right” amount of lash can vary quite a bit.
As a rule, running solid lifters on a hydraulic cam will reduce the effective duration of the cam at lower rpm. This will move the peak torque and horsepower curve to a lower rpm range, which may or may not be advantageous depending on what you are trying to accomplish. If you use hydraulic lifters on a cam designed for solid lifters, the power curve will tend to move up a bit but there will also be an overall loss of power and torque compared to what the cam would normally deliver with solid lifters. The best advice is to use the type of lifters (solid or hydraulic) the cam was ground for rather than trying to change one for the other. yea right, now where would be the fun? but caution is in order since the grind pattern makes a big diff.