There were 3 displacements of the scalloped valve cover big blocks, 348, 409, and a very few NASCAR 427's. The big problem was the cylinder head design, which made the engines suceptible to swallowing valves above 5500 RPM. Keep one under 4,000 or so, and it will live for a long time. The 348 engine was on the drawing board, almost ready for production, as a medium-truck engine in 1957 when the supercharged Ford 312's started eating Chevy's lunch at the drag strip. Chevy came up with a solid-lifter camshaft and a 3X2 intake manifold, and dropped the engine into the 58 Impala. In 1962, the size went up to 409, and when the FIA set the maximum international race engine displacement at 7 liters, Ford and Chevy both upsized their engines to the max displacement. Chrysler already had a 426, and Pontiac decided not to upsize the 421, since it was close to maximum already. The 429 Cadillac engine was already too big, but Caddy hadn't participated in racing for some time anyhow.
Jerry
