Quote: I wouldn't hesitate to say these last two posts are over the heads of 95% of the readers of this discussion. Oh yeah wher's my free stuff.
The concept would be easier to communicate if I took the time to post a picture. Or better yet, a short video would fully explain it in just a few frames.
I first read about the low pivot concept in a GM engine book years ago. The author didn't explain it fully but it sounded interesting. Years later I finally sat down at the CAD terminal and figured it out. The math is too complex for me so I solved the equation graphically. What you're trying to do is to solve the smallest product of load and scrub. When the valve is closed the load is small so you allow a lot of scrub. When the valve is full lift you're at max load so that is when you want zero scrub.
When you solve the equation you end up with the rocker arm perpendicular to the valve stem at about 2/3 of lift. This is below the mid-point theory which is more popular. The mid-lift approach is a simple approach that works pretty well in most applications. But if you're setting up something with 800 or 900 lbs on the nose then you might want to minimize the scrub under load.
