I've got a 455 in my 56 Olds, with a modern radiator. It sits pretty close to the engine, so the original clutch fan won't work. I'd like a 7 blade fan to take it's place, but the 4 I have in my shop have the wrong bolt pattern. I though a couple might be GM fans, so now I need to find a good fan, with the correct bolt pattern. What should I look for?

 

You could get a high cfm electric fan to put in there.

 

$70 7 blade fan. Located in Dallas,TX

 

Heartily recommend GM 7 blade fan in the right diameter for your shroud opening (you have a shroud, right?). Could be 17”, 18” or 19”. I suspect GM had many, many fan designs trying to optimize fan CFM across the radiator vs. noise & size. Stay away from the flex fans: interesting idea, but not that great in practice. At least in my experience.

If you go GM style, mechanically you’re looking for 1) the 4 bolt/nut connection between fan clutch and water pump and 2) 4 bolt connection between fan & fan clutch. American manufacturers from Olds to Chrysler kept these interfaces pretty standard for decades, so you’ll probably not go too far wrong, just have a look at your water pump snout before shopping so you know what could connect to what.

For GM fan outer-diameter-to-shroud-inner-diameter distance, it’s smart to leave at least a 1/2” or more. It’s an optimization: too small of a fan and you’re not pulling as much cool air through the radiator as you could; too big of a fan diameter and when the engine torques or you crack/break a motor mount and you’ll have the fan hitting the shroud circle. Or worse — fan blades meet radiator fins to destructive effect…

You can also go electric, but you’ll need to beef up your electrical system to handle the high amperage draw, maybe install a fan relay, and have some method for switching the fan on/off. Anyway for simplicity I opted for factory style fan clutch and 7 blade fans.

If you go GM 60’s factory style, get a 7 blade fan. In the boneyard, these are often from 70’s cars. Lower compression, smog controls, and retarded timing all put demands on 70’s engines that made them more prone to overheating. To compensate, GM deployed better fans. If you find multiple options in the junkyard, get several if they have different blade angle and depths. They will sound and perform differently and you’ll want the best one, so if you have a bunch to choose from, highest chance for success.

Next go through the Hayden fan clutch catalog and see which one might fit your physical environment best. This will be trial & error. I’ve tried a bunch for my ‘66’s which are essentially stock. Mixing and matching a 455 into a 50’s car means you’re in creative territory. So, innovate. Here are my notes for a 455 big block in a ‘66 big car:

Hayden clutch fans 2705 SD, 2747 HD, 2765 SD, all fit. but 2747 has .5" radiator clearance and is both cool and very noisy. 2765 runs quieter but hotter. 2747 with 7 blade deep fan runs noisy. Get shallower 7 or 8 blade fan. Check Hayden 2772, 2797, seems like it will be too long in overall length. Added 2747 to 6 blade quiet fan 4/16. Switched to 6 blade and 2765 in 12/16.

If I were going custom, I’d measure the distance between the end of the water pump snout and the back of the radiator first. Then take away 1/2 - 3/4” to be sure there’s clearance between the fan blade front and the radiator fins. Then go looking for the Hayden fan clutch which has a length closest, but shorter, or equal to the rad-snout distance -1/2”.

Hayden makes SD (standard duty) and HD (heavy duty) clutch fans. If I recall correctly the SD fan clutches kick in at a higher temperature (i.e. later in the heating cycle) than the HD fan clutches. So if over heating is a problem go HD since it kicks in before the engine gets hot. But be aware that the HD fan clutches make more noise. So, unless overheating is a problem, go SD to have a _quiet_ cool car. Who wants to hear fan noise? Well, at least, not me.

Hope that some of this is new & useful to you. I suffered prone-to-overheat cars for decades. It’s a great feeling to sit in traffic in confidence that you have cooling capacity & efficiency to survive modern traffic in ancient cars.

Cheers
cf

 

I had a 17" fan that I used to make a shroud for. Stupidly, I never checked the bolt pattern, or center hole. I made a wooden circle with the correct holes (measured from the water pump, not the fan I wanted to use), and bolted it to the pump. Then built the shroud around it. When I went to put everything together, I found that the fan didn't fit. Searched the shop and found another fan or 2, but none fit (except the flex fans, which I won't use). I might have a machine shop make a centering adapter, and oval out the mounting holes.
Bee Saint Louis, that is a clutch fan. Without the clutch. I have no room for that type. And personal preference, I don't want an electric fan.

 

The only factory non clutch fan, direct bolt on that I know of has 5 blades and were used on the early Toro's without AC. This would be the style that takes the spacer hubs not the clutch fan bolt pattern.