It is a long story about the engine. It came from the factory with a 4 barrel cam, 415/425 lift and 10.5 comp pistons but it had a 2 barrel carb on it.How Grand Dad pulled that off know one will ever know. It ran very strong. Grand dad in 1969 thought it needed a little more air, so he put a 4barrel manifold on it with a carter 625cfm carb. I rebuilt the engine a few months ago and replaced the 625 with a 500cfm carb for now. I found quite a few interesting casting numbers on the internal parts when I took it apart.Welcome from Canada, Is that a factory 273 four barrel?