so according to the CRB the displacement is the key factory
so a DOHC 1.6L honda = DOHC 1.6L Toyota (160hp v.s 112)hp?

You can use displacement, as a base point, however to accurately classify each car you would have to have alot of data on the motor and every variation of the motor. If you took displacement, CR, valve size/# of valves, cam lift/duration/lobe centerlines, valve spring rates, weight of rotating assembly, cylinder head/intake/TB, volume of runners, fuel supply, etc...

Then you can plug it into a modern enegine simulation and get an idea of what it will make with IT legal mods.

Even older engine programs are not detailed enough to handle everything , and when we are talking every hp=17lbs it woudl have to be quite accurate.

Then how do you get this information for all the cars in the ITCS? Then if you get info from members is it gold?

They have to take more than displacement, otherwise the 2.3L ford mustang would be in ITA, and the 99 civic si would be in ITB.