Rocker Clarification is up!!!

[X-TECH MAN]

Originally Posted by Greg Reimer 7376

Seems that the last several posts have verified what I wrote in my post on page 2. We need to look at some absolutes- two sources of absolutes come to mind- those provided by the engine designers, and those mandated by the sanctioning body.
Absolute #1-- Valve lift must be OEM or as specified.
Absolute #2-Rocker arm ratio must not exceed OEM.
Cam lobe lift isn't too well specified. In order for #1 above to be achieved in a desireable fashion,#2 has to be followed as well. In the case of a small block Chevrolet,ideal results are when valve lift is half again lobe lift.In the event lobe lift is correct,and valve lift is lacking, then another means has to be employed to achieve it. That is where push rod length comes into play. Now, you don't really want exact specs here, you want to be safe by .005-.010". This is because the tech guy at teardown might not read mikes the same way I do. Also, expansion due to heat might cause results to vary. If my intake lift spec is.390". I would love to see an actual.379-.382".Now, if I achieve this spec with a very long pushrod, I'm getting the maximum extra duration and rate of lift out of that valve train.
Now, the other booby trap has to be recognized. If you checked lobe lift, it passed right on the number, used a very close to optimum, a long push rod, you could still result in a rocker ratio that is a bit over, however,that couldn't help but make the valve lift over as well.Optimally, a cam lobe with the correct lift, a valve with lift good by .008-.010, and a rocker arm ratio of 1.47-1.49 would be the best of all worlds. Now, good luck getting it!

Any good machinist reads the "Mikes" the same way. I dont know about other tech guys but I used a dial indicator when I checked lift (and duration/overlap) in the old days. The Govt. spec. on tolerance of either a mike or a dial indicator is plus or minus .001(one thou.) My personal tools were alway certified by myself. ....I worked almost 18 years in a Navy Calibration lab after working as a tool maker for the Navy. Its not rocket science.