IML: valves and heads

There were some 2.08 - 1.74 heads from 62 thru 64. The 62 383-2-4bbl 343HP, 300 H 413-2-4bbl were the first engines, 63 and 64 300 letter cars, with 2-4bbls. Since they all had 700-800cfm carbs,and larger cams Chrysler saw fit to improve the valve size. These additions, reduced low end torque, and raised peak torque RPMs, a 3.31 axle ratio was the standard choice. Since we are discussing Imperials, the low end torque is important. It would take the "package" to see real improvements. The standard 413 head is fine, since the "package" was designed for low speed, and was a compromise between performance and economy. In fact the 413 truck-motor home engine had 1.85-1.5 valves, and a milder cam 7.5:1 compression, to raise peak torque at a lower RPM. The late 452 head does provide some advantages, hardened valve seats, lower compression (for poor gas quality) and improved cooling passages. As far as the larger valves, I don't think the "Fannyometer" will detect it. Ya'll have a nice day, Dave.