[viking]

- per holley -

A competition or race engine which has installed a long duration, high overlap
cam will have low manifold vacuum at idle speeds. If the vehicle has a
manual transmission, take the vacuum reading with the engine thoroughly
warmed up and at idle. If the vehicle is equipped with an automatic
transmission, take the vacuum reading with the engine thoroughly warmed
up and idling in gear. In either case, the power valve selected should have
a vacuum opening point about 2" Hg below the intake manifold
vacuum reading taken.