PRELOAD!!!!!!!
I MEANT PRELOAD!
Most run a half turn down from zero. That advice is from the OLD DAYS when lobe design outpaced spring design, and valve float was a normal occurrence with most performance cams. When float occurs, the lifter will fill up the oil chamber and hold the valve off its seat, possibly allowing valve to piston contact, and destruction. This is also why cam companies say you need .100" to
125" valve to piston clearance.
With modern computer designed lobes, and better spring materials, float is mostly a thing of the distant past.
Preloading at a "half turn" or .025/.050" can allow as much as .100" of plunger travel to bleed off under higher rpm, boost, hot oil, or the amount of spring pressure required on a turbo engine to keep the valves closed against boost in the intake tract, or back pressure in the exhaust.
All Hydraulic lifters bleed off to some extent when running, or off, if the engine is shut off with a valves, or several open.
That's why it's common to have a few clicky lifters on startup until oil pressure refills the chamber under the plunger.
The deeper the preload, the less the amount of lost lift and duration will be when the oil is bleeding past the plunger.
On a hi perf/high spring pressure application, many of us run the preload a half turn UP FROM THE BOTTOM!
This limits the loss of lift and duration to a maximum of that amount.
An adjustable valvetrain (which our v-6s don't have), setting preload is easy. In our engines, bleed off all the lifters one at a time, and replace the pushrods with longer ones to put the plunger lower in the lifters. Smith bros. will make you ANY LENGTH you require.
Serious racers limited to Hydraulic lifters by NHRA or engine design have 4 or 5 sets of pushrods in .025" increments to effect preload changes.
A solid roller cam and adjustable valvetrain is an easy, but not cheap solution. Several sets of different length pushrods is cheaper, if you care enough to get that last bit of HP.
Speed costs money, how fast do you want to go, or more simply put, how often are you prepared to lose.....
TIMINATOR