Wrong heads for a 273

dibbons said
My personal experience on bracket racing 273. Combustion chamber volume not measured in either case:

Stock 273 heads, (port matched to 340 intake gaskets), 10:5 to 1 factory Commando style pistons (forged TRW). Block decked (cleaned up cut), heads milled (cleaned up cut). Edelbrock Tarantula intake (made for 340) and Holley 600 CFM double pumper. Steel shim head gasket. Cyclone fenderwell headers and Isky camshaft. Best E.T. 12.72.

Same as above with 340 open chamber heads (2.02) and cylinders notched for valve clearance. Best E.T. low 13.00's.
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I never ran the 72 340 head 273 at a track and never had headers on the car, but I can tell you that it was much faster with the 340 heads, cam, intake and TQ than the 273 heads, 284 duration TRW cam, Offy intake and 600 1850 Holley.