A/C made all cars more salable when it came to trade in time. A car that didn't have A/C would sit on a dealer lot for about 50% longer even back then as a race type engine in it. The lower rear gears in the 455 & SD cars were because the cars were much easier to get moving because of the low end TQ . The RA IV didn't start making power until you got it wound up a bit. The RA IV cars had to be up around 2500 rpms to get them working. The 455 & SD would make power at 1200 rpms & didn't need high rpms to get going. It had it way down low. PLus the 455's & SD cars were all done at about 5500-6000 rpms. Were as the RA IV cars needed the higher rpms to work better. Below 2200 rpms the cars would fall on there face with gears that were low. Thats why it got 433's & 390's. I run what would be considered a RA IV engine with the E-heads & a Crane Blue print cam. Once I get it up over 2000 rpms it really wakes up.
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