Can anyone tell me what GM 18" clutch fan would have the most blade pitch? Also, which clutch would have the lowest "locking" temp? I need to increase my low rpm air flow.

Thanks in advance for your responses.

The Hayden or Imperial "Severe-Duty" clutches will have good lock-up characteristics (they spin at about 90% of water pump speed).

those are good questions 6T7ss. i run a fairly high dollar ($60) hayden clutch on a 7 blade fan off of a '68 toronado with air. i agree with GS455, it is stiff and seems to almost turn water pump speed so you lose a bit of HP with it, but man does my setup pull air. it'll blow your hat off.

Do not know year you are working with. a 3947772 fan blade is for a 3:31 rear. 1970 Bob

Do not know year you are working with. a 3947772 fan blade is for a 3:31 rear. 1970 Bob


I have a 67 SS with a 3:31 rear. I ordered a 3947772 fan today, now if I can determine the proper clutch that locks up closer to my operating temp, it should give me the air I need.

The Hayden or Imperial "Severe-Duty" clutches will have good lock-up characteristics (they spin at about 90% of water pump speed).


I'll check into the "severe duty" clutches as soon as I get my fan in.

Thanks for the info.

those are good questions 6T7ss. i run a fairly high dollar ($60) hayden clutch on a 7 blade fan off of a '68 toronado with air. i agree with GS455, it is stiff and seems to almost turn water pump speed so you lose a bit of HP with it, but man does my setup pull air. it'll blow your hat off.


Talk about high dollar, I paid like $120 for the clutch I'm running now and I don't think or feel like it's hooking up. It's stiff to turn with the engine off, but, I never seem to hear it "lock up". With the engine hot and idling, putting your hand in front of the radiator, I can barely feel any air being pulled through the radiator.

i just happened to have called hayden yesterday since i am looking for the proper fan clutch for my 454 with 18" 7 blade GM fan blade

i intended to go with a Severe Duty (Imperial 215052 ) which requires a 2 1/2 inch pitch fan blade

they measure pitch by placing the fan on a flat surface and measuring the height of the flat surface of the trailing edge

my GM fan measures 2 1/8 " pitch

if you use the severe duty clutch with this fan (or any pitch less than 2 1/2") the clutch will NOT diengage and will run at engine speed at ALL times even when cool

the better coice seems to be the hayden 2705 which is the SAME as their Imperial 215049

this is what the tech support guy told me and this can be confirmed by calling them directly

i called several parts houses and none of them list fan blades by specs such as pitch so i just couldnt find a fan blade that would be consitent with the specs of the severe duty clutch

What seems strange to me is, my fan pulls air like crazy when cold. You put your hand in front of the rad and you can feel the air being pulled in. When the car is hot and it should be pulling air like crazy, you can barely feel any air at all. Sounds like total reverse to me. I'm running a Hayden 2797 clutch and a repro 3947772 fan. The car is still heating up in traffic, it's getting very frustrating!!!!