HIGH SPEED LIFTER BLEED DOWN
Every time a valve is opened the lifter bleeds down some.
Because aftermarket lifters do not seem to hold the close tolerance needed between the piston and the body of the lifter some bleed down faster.
It is this bleed down that starts the problem.
At high speed air trapped in the lifter reservoir enters the working area making the lifter spongy and noisy.
From 1950-52 Chevrolet must have had this same problem keeping close tolerances in their lifters so they vented the lifter by grooving the bottom of the push rod.
For jobs where the lifters are already installed or to prevent trapped air, you can vent your lifters by grooving your push rods on the bottom face.
It only needs a shallow groove from the center to the edge to allow air to escape.
This will only work with lifters with a vent hole in the push rod seat (which are the ones that seem to have the problems).
I have done this many times and recommended it to others with 100% results.
It is also a good idea to pre bleed your lifters (per shop manual instructions, not just soak in oil).
Here is a link to a 1950-52 push rod grooves.
http://picasaweb.google.com/pre68bo...v1sRgCOO2tJ767rre2gE#5327689421263380850
