This may be too general of a question, but I have heard that for every 2 degrees in lobe seperation change that the v-p clearance will change about .020". Is this true or does it depend on the camshaft.

Thanks in advance. smile.gif

depends on the intensity of the lobes.

Yep, depends what type of lobe you're talking about (roller, flat tappet, etc..) but just as important will be the ICL. If you have a cam with 106lsa and 106ICL and you turn around and have the same cam ground on a 110lsa and install it on a 106ICL you will have the same intake clearance but more exhaust clearance than the 106/106.

Darren - Your .020" figure is a little conservative. I believe that .015" - .018" will cover most lobe designs. But, to clarify, it is the change in the installed center line that actually effects the piston to valve clearance. (This could come about due to a change in the lsa.)

For example, a cam with a 108 lsa installed "straight up" will have a 108 ICL and a 108 ECL. This same cam installed 2 degrees advanced will have a 106 ICL and a 110 ECL. This will result in a decrease in the intake ptv clearance and an increase in the exhaust ptv clearance.

The same lobes ground with a 110 lsa and installed 4 degrees advanced (106 ICL and 114 ECL) should have identical intake ptv clearance, but .030" - .036" additional exhaust ptv clearance (relative to the 108 lsa cam, installed 2 degrees advanced).

Hopefully this demonstrates that the ptv clearance is a function of the installed centerline, not the lobe separation angle.