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HD Fan Clutch

aknight_sa

aknight_sa

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was looking for a new fan clutch online for my 84 blazer with 1 305 SBC..

i saw some fan clutches with a title of Heavy duty on some of them.. i do live in a very hot weather area in the world which reaches above 120 F in the summer.. so i just wanted to know whats the difference between them and other clutches? should i get one or just a normal AC Delco Clutch?
 
dangerdog said:
Electric fan and free up a bunch of horsepower.
Click to expand...

A "bunch of horsepower"?? No. The gain is +/- 10hp.

If you want a super strong fan clutch, use this application -

83 K30 dually, 454, 4spd w/4.56 gears. The gear ratio make a difference, this is a severe duty clutch and when used with a 7 blade fan cools amazingly well.
 
aknight_sa said:
was looking for a new fan clutch online for my 84 blazer with 1 305 SBC..

i saw some fan clutches with a title of Heavy duty on some of them.. i do live in a very hot weather area in the world which reaches above 120 F in the summer.. so i just wanted to know whats the difference between them and other clutches? should i get one or just a normal AC Delco Clutch?
Click to expand...

Some of what the aftermarket was selling for fan clutches in the past were lacking the thermal portion. The coil up front is to regulate the temp that the fan comes on at, apparently the cheap ones (non-HD according to some aftermarket manufacturers?) simply omit that from the design.

AFAIK there are different fan clutches, but without changing the number of blades, not sure how it would make any difference. I'm guessing somehow the HD clutches "lock up" more solid to keep the fan from slipping under the load.
 
Last edited:
nvrenuf said:
A "bunch of horsepower"?? No. The gain is +/- 10hp.

If you want a super strong fan clutch, use this application -

83 K30 dually, 454, 4spd w/4.56 gears. The gear ratio make a difference, this is a severe duty clutch and when used with a 7 blade fan cools amazingly well.
Click to expand...

Is the clutch for the 454 going to work on a 305?
 
Yes, same bolt pattern on the water pump hub. This is a standard rotation application so it'll work as long as your 305 hasn't been converted to a serpentine (reverse rotation) set up.

If you go with this application, make sure the part number is different for the 4.56 clutch than other versions of the truck. If it's a one size fits all big block part number then it's not the mac daddy unit.
 
Well, I just spent a couple of minutes hitting Rockauto, NAPA, O'Reiily's and such but no one spec'd a different unit for the low geared truck. GM may have been the only one to actually do it whereas aftermarket stuff is more generic.

I would imagine as long as things like "thermal" and "severe duty" are in the description it should be a good strong clutch.
 
Can't remember the name of the show. But they dyno tested all the different types of fans. I believe none of them robbed less then 10 HP the worst was a solid stock at like 27hp. So in my case it is a bunch!
 
Pretty much every test they have done in that series is informative to some degree. Certainly much more dyno testing and parts swapping than I could ever hope to afford.
 
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