Editing Z31/camspecs (section)

==== FINDING EXHAUST LOBE CENTER ====

Once again 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 exhaust opens BEFORE Bottom Dead Center. Example would be 44 degrees on the degree wheel BBDC.

Now go over the top on the lobe until your indicator is .050 inches off the Base Circle. Now you should be where the exhaust closes AFTER Top Dead Center. Keep in mind to continue turning the engine in the same direction it runs and DO NOT BACK UP. Example would be 8 degrees on the degree wheel ATDC.

You can now calculate your duration. The valve opens at 44 degrees, plus it closes 8 degrees, plus 180 degrees (the distance in degrees between TDC and BDC). Your duration at .050 inches of lift would be 232 degrees.

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

'''Please Note: '''If you have a low overlap cam, the exhaust closing may be BEFORE 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 exhaust closing figure. This would normally be the smaller number of the two figures.