Lifters

Pishta,
Don't know how to post on the forum but happy to email pics if you PM me an email address. Can be done on hyd & sol lifters, good because you cannot put EDM holes in hyd lifters...

On the Rhoads lifters. The inner piston had a groove [ like a thin slot ] top to bottom which gave a controlled bleed down rate. My understanding is that Comp, Crane etc could not copy the design because of a patent. So they used 'selective bodies & pistons' to control the gap & therefore bleed down rate; not as consistent in bleed down as a groove.
I modified std lifter to work like Rhoads by filing a flat on the inner piston. About 0.100" wide would provide a noticeable increase in idle vacuum & only a slight noise increase.