Budget Rocker choice

NM mentioned low performance and cruisers above
I do not see where roller tip rockers are justified for these builds.
I think of the jackrabit oill pumper curved arm that keeps the cable straight and right above the hole when it goes up and down
move it up or down from where it was installed it would not work
I posted a quote from a well respected head guy/ engine builder who said that anywhere the stripe is on top of the valve (not running off the edge obviously) is ok
but if the stripe gets wide then guides are gone real quick
I think it was Chris Straub but could have been someone else
anyway back to the oil well analogy
Think not of the rocker and the valve tip but look at the motion from the side
like an arm coming from the center of the shaft with an ARC on the end - the arc is the length of the shaft to the middle of the roller of foot
now sit the end of your valve touching the arc and rotate that point on the arc
see what a difference it makes if the touching point is in the center of the arc
or if the fulcrum is high as in Crane's "quick lift" method
or low the way a lot of builds come out with no correction
two high u get overarcing with the rocker pointed way down
the other you get "underarcing"
You get underarcing with long valves or roller tip rockers,
What YR said
"Broken parts. Needing more spring pressure for the same or less RPM. Rapid guide wear and the beating up of the valve job that follows."
WHY?"
because you get the most rocker ratio when the (arm and roller) are at the point perpendicular to the valve stem
back to the ARC not hard to see when the rocker is up the arc or down the arc you have less valve motion per degree of rotation
or pushrod lift on the arc on the pushrod side- double trouble
NOw if we have that maximum multiplication nearer to maximum valve lift what is the cam trying to do
That's right
slow down the velocity to 0 when the lifter is going over the nose- and the rocker is fighting this deceleration
which is why you need the stronger springs, float the valves earlier, float the valves
and floating the valves brakes parts
As does closing to quick and getting valve bounce- that's where too low a piviot helps a too quick cam design like the Comp HL series by ODHarold
Harold learned and that's one reason the Lunati versions are a better compromise- Ultradyne somewhere in between.
Harold had enough computer power to be able to have many more polydines and many more paramaters in his later designs
You can look at the problem graphically as I suggest with my "MIDARC" or do the math