Editing Z31/camspecs (section)

==== FINDING INTAKE LOBE CENTER ====

Remove ALL lash. With your dial indicator on the retainer or follower, rotate the engine in the direction it would normally turn, and come up to .050 inches of lift. Write down that figure from the degree wheel. This is your opening figure. This is when the intake opens BEFORE Top Dead Center. Example would be 10 degrees on the degree wheel BTDC.

Now go over the top on the lobe until your indicator is .050 inches off the Base Circle. Now you should be where the intake closes AFTER Bottom Dead Center. Keep in mind to continue turning the engine in the same direction it runs and DO NOT BACK UP. Example would be 39 degrees on the degree wheel ABDC.

You can now calculate your duration. The valve opens at 10 degrees, plus it closes 39 degrees, plus 180 degrees (the distance in degrees between TDC and BDC). Your duration at .050 inches of lift would be 229 degrees.

You can now calculate your lobe centerline. Divide your total duration by 2 and subtract your intake-opening figure. This would normally be the smaller number of the two figures.

104.5° would be your lobe centerline.

'''Please Note:''' If you have a low overlap cam, the intake opening may be AFTER TDC, if so, you will have to SUBTRACT that figure from the closing number and add 180. This will be the duration at .050 inches of lift.

You can now calculate your lobe centerline. Divide your total duration by 2 and add your intake opening figure. This would normally be the smaller number of the two figures.

114.5° would be your lobe centerline.