I see this an awful lot. Has anyone stopped to think what a hydraulic lifter really does? Think about it. It automatically compensates for lash with an oil fed plunger. That's it! It will not hold the valves open if you have too much preload, and they do not pump up from high rpm and oil pressure. The anti pump up lifter is a misnomer. When the engine gets into valve float, there is clearance, aka lash, between the valvetrain components. The lifter does it's job, and closes that lash. Now when the valve tries to close, the lifter is pumped up and won't allow it to seat. Enter the anti pump up lifter. They add a heavy duty retainer, and instruct the engine builder to only run .002" preload. That way when the valves float, the lifters won't fly apart, and the valve will seat enough to not drastically lose power.
I have run hydraulic lifters with the plunger depressed to within .015" of bottoming out, and made lots of power. The valvetrain geometry better be right, and it better have adequate spring to control the valve for the intended rpm. For what it's worth, I run my street builds at 3/4 to 1 full turn on every hydraulic lifter type, including anti pump up. They run quieter, and because I make sure the geometry is right, they don't pump up. The motor really doesn't care where the plunger is riding inside the lifter. It only cares if the valve opens and closes properly.
