Why do fan blades have a part number? The MAIN reason is the rear end ratio, Say What? For example a 1970 fan blade # 3947772 is designed to match a 3:31 rear end ratio. This may be why a 772 blade is in demand by 1970 owners, The 3:31 was the standard rear end ratio for most all SS cars, A 4:10 was also an option.
Every cooling system needs XXXX cubic feet of air, For the system to operate at 100%. Different systems or engines generate more heat than others. If all seven blade fans were the same, WHY the part number?
It is the " PITCH " of the blade that determines, How much air is drawn into and through the " Heat Exchanger " or Rad. and the engine compartment.
This is something that a lot of folks overlook and then have heating issues, Then start spending cash on this and that. If a 100% stock cooling system worked 40 years ago, But not good today, Excluding bad parts something has been changed.
My 70 driver, A 468 with stock (134 ) A/C has NO cooling issues. Everything in the engine bay is just as it was in 1970. For a driver or a street driven, Now and then down the track, A stock system is fine. A pure race car.. Forget all of the above.
Dem Chebby guys had figgered out, Purdy good Bubba.........