IC is the intake center line. That's the "where" reference about where the cam is installed in the engine. When you look at cam specs, you see lift, duration, lobe separation, valve events.....the IC is the amount away from the lobe separation the cam is installed. Say the cam has a 112 LSA or lobe separation angle. A popular "place" is 4 degrees advanced. So that means the cam would go in at 108 IC or 4 degrees advanced from that 112.
