Explain ADJUSTABLE ROCKER ARMS to me.

[bronco italiano]

Going to disagree. I'm pretty sure the "perfect perpendicular" should happen at the point where the load is maximized, and therefore should occur where the valve spring load is highest. The highest spring force occurs at maximum lift, and that is the point where you want to optimize.

If you want to build the most stable valve train geometry, the roller tip contact line would be exactly centered on the valve stem at maximum impulse. As an example, a high performance spring seat pressure might be 200 lbs, and the open pressure might be 450 lbs. The load (and impulse) at max lift is vastly larger than the impulse anywhere on the ramp.

The only reason to center the rocker tip at mid-lift is if you sell camshafts (or rocker arms) and you don't want to do any actual engineering. It's "safe."

Anybody can hop around on a pogo stick with one leg. But if you want to maximize your height on a pogo stick, you want both feet on the pegs when you hit bottom.

That makes so much sense. On air-cooled VW's they always talk about perpendicular at half lift. But, as spring pressure increases upon opening it will place more stress on the pivot point as it moves away from that perpendicular plane. I gotta research this more!!

 

[Broncobowsher]

This is why rocker arm geometry gets fuzzy.
Now the spring loads, those get funny at speed as you are now dealing with inertia, acceleration, deceleration. The static test loads are not the same as the dynamic loads. Get into some valve float and there are times the valve is open and there isn't any spring force on the rocker as the valve train is floating.

 

[Oldtimer]

In the interest of me learning, I am asking questions.
Perfect perpendicular at full open (100%) would maximize leverage at full load.
Perfect perpendicular at mid lift (50%) would minimize roller travel across valve stem.
Folklore says to set rockers at 2/3 travel (66%), maybe an experiential result.
Since I have to purchase and install as designed parts, which of the above is the “best” compromise?

 

[jamesroney]

In the interest of me learning, I am asking questions.
Perfect perpendicular at full open (100%) would maximize leverage at full load.
Perfect perpendicular at mid lift (50%) would minimize roller travel across valve stem.
Folklore says to set rockers at 2/3 travel (66%), maybe an experiential result.
Since I have to purchase and install as designed parts, which of the above is the “best” compromise?

The one that uses the “most available” components. It’s not worth spending $150 for custom length pushrods if the factory length ones are “close enough” and half price. If you are not going to spin it higher than 5k RPM, “good enough” is more than good enough.