What changed the rated horsepower RPM in 1953/54?

Posted by Jack Vines On 2009/10/20 15:15:30

Just reading through the chart, Packard rated everything at 3,600 RPMs for many years. In 1953/54, the horsepower peak was 4,000 RPMs. Yes, the compression was increased, but only the port design and camshaft duration really changes the horsepower peak. Did either of these change in '53? What year was the first use of the 4bbl?

thnx, jack vines