Have 66 SS with original 66 BB water pump, 4 blade fan, & radiator and have added a shroud. Understand I should change the fan spacer to move the fan back. What % of the fan blade depth should sit outside of the shroud to provide maximine air flow for cooling? Think the blade depth is approximately 2". Fan spacer is 2 1/4" Fan blade presently sits about 1 3/4" inside and 1/4" outside of shroud. Thanks.

Fan should be half in half out.

Fan should be half in half out.
Yeah...to be most efficient.

Thanks, then that would mean about a 1 1/2" spacer. Think there is a common one off the camero's that 1 1/2"., I assume that it will fit.

Yes, half in-half out!

The spacers come in all differant sizes. I best ones I have found are the billet aluminum ones made for the circle track guys. They are real slick and stoutly built.

Good Luck :D

FYI,those stock 4 blade fans are not very efficient at all,the stock gm 7 blade fan & fan clutch used for ac & HP setups like 396/375hp are much better cooling/flowing fans when compaired to the stock 4 blade.

Scott

Thanks Scott, I have what I think is the 7 blade fan that GM parts direct sells. But kind of wanted an original look. Rebuild an original 66 BB radiator this past winter & put an original fan in: and so far the max temp that I have driven it in is 85F and no problem down the road or at idling; but doesn't push near the air the 7 blade fan did last summer when idling. So thought maybe moving it out would give me enough air for cooling when at 95F. Original application with shroud call for a 1 1/4" spacer.

Jim,i believe clutch fans were opt on your 396 (for H/D cooling opt/AC opt/and 375hp)for that yr so it would still be the stock oem look your after.

You also said the clutch pulled more air through your radiator @ idle/low speed which is what a BBC needs on hot days esp in stop/go traffic.

But if your trying to win a 100 point carshow and your car's build sheet didn't show you had the clutch fan as an option then i would see why you don't want to run it. But other than that why bother with the 4 blade fan since the clutch fan is a factory opt and corrrect for your car?

Scott