Rocker arm recommendations?

B3,
Somehow I don't think you are going to get it.....


Post 67, where you are fixated with [ wrongly, for the umpteenth time ]: 'The length remains the same'.
It is not what I have written that is utter & complete nonsense....
You talk about ratio changing because valve lift is lost. Yes, you got that right. Ratio change. Buuuuut that is not the only thing that happens with the rocker going from valve closed to valve open. Two other things happen concurrently:
- both the p'rod side & valve side travel through arcs. There is lost motion on both sides of the rocker due to the arc motions that are transferring a circular motion into a straight line [ prod & valve move essentially in a straight line ]. Depending on how the particular rocker is dimensioned will affect if & how much valve lift is lost.
- using a ball/ball prod as an example. The prod ball is a smaller radius than the rocker cup. How do we know? Because if the ball was bigger, it would not fit inside the cup, or would jam. The ball makes point contact inside the cup; the ratio on the prod side is that length from that point of contact to the fulcrum centre. And it changes as the rocker moves through it's cycle, changing the ratio on the prod side. And the position of the contact point in the arc also causes a change in rocker movement & therefore ratio.


The combination of the change in the arc plus the contact point of the prod & roller tip is what gives the overall ratio & it changes throughout the rocker travel.
This is how the Crane quick lift rocker works; the prod cup is lower. That actually looses some straight line motion [ prod ] because of being further down the arc; but counteracting this is the fact that the ball contact in the cup is closer to the fulcrum pivot. The ball contact position wins out & creates the early lift increase.

For those trying to understand the ratio change on the valve side. Imagine a shoe type rocker that is identical in shape to a roller tip rocker. Grind the shoe on the rocker to the same radius as the roller on the roller rocker. Now using the shoe rocker, the point of contact on the shoe changes during the rocker cycle. The ratio is the distance from the fulcrum centre to the shoe contact point it changes. Exactly the same thing happens with a roller rocker; it is as if at any time in the lift cycle, the roller is welded to the rocker arm & is as one.