see if you can find Dulcichs' Mopar Muscle porting articles. Google it. Good info. You trim them on the outside edge of the black lines if using 2.08/1.74 valves. if using 2.14/1.81 you'd cut them out then use them in the leftover plastic to cut new ones that are wider by .060" (.030" on each side) for instance on the intakes (2.14-2.08=.060"