Tr Benj,
The 273 {Closed Chamber Heads} came form the factory with 3.3 CC' smaller
combustion chambers than the 318 {Open Chamber Heads}.
The 318 Heads did lower Compression about {-.35} of a Compression Point,
when compared to the 1965 thru 1967 {273 Heads}.
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The 273/200 HP
Was not available on the Automotive End. It was a 'special order' for Fleet Vehicles
{ie; Livery Vehicles {Taxi Cabs} and Light Transportation Vehicles}.
It was a 'basic' 273/180 HP, that had a 'stock' 4-Barrel Intake and Carter AFB
{500 CFM} from the 273 'Commando' added on the Engine.
