Good way to explain IT classes is this:
ITC: Small displacement pushrod or SOHC 8 valve 4 cylinder engines 1.7l and under (No 16 valve engines)
ITB: Small displacement 16 valve (1.3-1.6), or larger displacement 8 valve 4 cylinder engines (1.8-2.5)
ITA: Small to medium displacement SOHC and DOHC 16 valve 4 cylinder (1.5-2.2) Pushrod and SOHC 5 and 6 cylinder (Under 3.0l)
ITS: Medium to large displacement DOHC 16 valve 4 cylinder (1.7 to 3.0l) small displacememt DOHC 5 and 6 cylinder, large displacement SOHC or pushrod 6 cylinder
ITR: larger displacement high performance DOHC 6 cylinder, couple pushrod V6’s, couple very hi-po 4 cylinders
There is overlap in the classes, weight is now being adjusted to ensure competitiveness, however, no car is guaranteed to be competitive in it’s class. The Hondas are generally classed above where their displacement should dictate, but their suspension gives them an advantage (4 wheel double wishbone).