What is the correct way to find out which pushrod length your motor needs? TIA

 

I suggest you go to www.compcams.com and research.I know they explain it,you have to look.I think its under valvetrain geometry.They make an adjustable push rod to use and figure it out.

 

What Joe said. You have to measure, you really can't just figure it out.

Rich Krause

 

Are you asking how to measure? It takes a checking pushrod. You install it just like a normal pushrod, but it is length adjustable. I checked my length by putting some Prussian Blue on the top of the valve stem and installing the checking pushrod and adjusting lash. I rotated the engine by hand a couple of times to cause the roller on the rocker arm to make a pattern on the top of the stem. You want the pattern to be centered on the top of the stem. If it's off-center, you change the length of the checking pushrod and measure again. You do this until you get the correct length. Measure the checking pushrod and order the correct length pushrods.

There may be better methods, but this worked great for me and Prussian Blue is cheap and it wipes off when you're done.

 

http://compcams.com/information/Products/Pushrods/