Fan size vs shroud size
 

My 71 has a shroud that seems to measure 21" diameter. My fan is the stock 18" 772 (7 blade). I would like to upsize the fan to take advantage of the larger shroud to get the better cooling. What is the next GM stock size up (7 blade). 19" or 19.5?

I can't accurately measure my fan, 772, or shroud, stock 70 big block, with everything installed. I can tell you my shroud is roughly 1.5" larger diameter than the fan, 3/4" from fan blade to shroud times 2.

I can also tell you the stock 772 fan, stock matching shroud, Hayden 2747 HD clutch and a good 3 or 4 core rad, depending on engine, is about as good as you can get. Heard so many guys chasing an overheat problem, electric fans, aluminum rad and still running hot. Timing, not enough advance will cause the engine to run hot. Also a lean idle mixture will cause it to run hotter at idle. The original stock setup worked good but everything has to be in good condition, radiator and fan clutch. No different than any other system, if one part is not up to the task the whole system fails.

Sounds familiar.

Hay, I apologize John, didn't answer your real question. I don't know of another GM fan that is larger in diameter. They used another 7 blade in that era which is a little different design in the blades but also a good fan. Pretty sure it is the same diameter as the 772 though. I'll try to find the number and diameter and let you know.

Look for a 7 blade fan from a 72 Chevelle with AC, looks like that is a 19" but I don't have a GM part # for it.

EDIT: If you pull that 772 fan out, check the date codes on the blades. 772's are in demand and depending on date codes can be worth quite a bit.

I am in the process of fixing the high temp issue. I've taken some steps but still have a few others left. Step one was to replace the thermostat with a Autozone 160 with a bleed hole drilled in it. That alone has made a big difference. Next step was to get the Hayden 2747 and larger 7 blade fan if possible, and check timing. If I can't get a larger fan, I think the changes made will make a huge improvement with my stock 4 core.

If your not trying to go for matching numbers car im running a fan out of a mid 80's big block truck which is 19.75in. I ran it without a shroud for a couple years and never had a problem but recently made a sheet metal shroud due to a near finger loss. The fan comes up nearly an inch over the top radiator support and well I just wasn't paying attention. But I never saw temps over 180 at idle unless its the middle of a beautiful 120 California summer day. For those days there's a 17 inch electric pusher fan mounted on the front side of my radiator that's on its own temperature switch mounted to my radiator.

Fat fingered from the phone- Corey

fan
 

Here is a 19" I found...

Attachment 2232