Intake centerline is the measurement in crankshaft degrees after top dead center on the intake stroke where the centerline of the intake cam lobe is (point of maximum lift). It is generally the cam spec used to verify that the camshaft was ground and phased correctly in relation to the crankshaft. Camshafts are often manufactured off by a bit and need to be advanced or retarded with respect to the crankshaft in order for the ICL when installed to match with the value spec'd by the manufacturer.
