Seven Bladed AC Fan

[Al Grenning]

The seven bladed AC fan question has come up a number of times. Currently, the best view supports five bladed fan use in all A/C applications. However, one interesting observation is worth noting. While using Exception Control Letter tables in the study of 67s, along the trail there have been some interesting trends. One of them is this: On the very small number of L36 and L68 (390 and 400 HP) AC cars that appeared to be untouched and had original build documentation showing positraction gear ratios with Exception Control Letters of 3.36 and 3.08, - all had seven bladed fans. Unfortunately, virtually no sampling of small blocks with A/C has been done and the hand full of BB cars looked at does not provide a basis for hard and fast conclusions.

Also worth noting - part lists in the AC section of both 66 and 67 A.I.M. show a primary and "optional" fan. If the two fans were to be used interchangeably it would have been nice if the A.I.M. said so. Instead of the word "alternate" there is the abreviation "opt". Hmmm! ---- It would be interesting to see how many owners of BB 67 AC cars with tall ratios have the seven bladed fan.

Al Grenning

[Jack H.]

Re: Seven Bladed AC Fan

Al, that's what 'OPT' means in AIM parlance -- assy line choice for substitution. You'll see the same under fan clutch call out and flasher assy where discrete PN's were maintained to track different vendor's assy's (Schwitzer bar vs. Eation coil fan clutch and Tung-Sol, Signal-Stat, Ideal on flashers). The wisdom of creating separate bins for certain parts via discrete PN's vs. common bin mixed with functional equivalent parts from multiple sources appears to be lost to us today, but both practices were done and as the AIM was intended to be a GM internal document there was no need to define terminology....

[Jack H.]

Re: Seven Bladed AC Fan

Al, that's what 'OPT' means in AIM parlance -- assy line choice for substitution. You'll see the same under fan clutch call out and flasher assy where discrete PN's were maintained to track different vendor's assy's (Schwitzer bar vs. Eation coil fan clutch and Tung-Sol, Signal-Stat, Ideal on flashers). The wisdom of creating separate bins for certain parts via discrete PN's vs. common bin mixed with functional equivalent parts from multiple sources appears to be lost to us today, but both practices were done and as the AIM was intended to be a GM internal document there was no need to define terminology....