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Trying to get the biggest volume of air through my big block radiator, I'm trying to figure out which FAN would be better to run. The 7 blade and the 5 blade, both seem to have been available back in 1970 so determining which is best for the big block has me wondering. Would you go with a 18" fan with 7 blades or 5 blade? Why did GM design the difference? I believe the 5 blade design went to Yenko but not sure which is better?
 

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The 1970 L78 had the weird 5 blade fan and no clutch. Part of the reason for the change was the howling mentioned in the post above. I had a different fan on my 1970 SS L78 when I bought it. The noise was so bad you could hardly hear the wonderful sound of that 402 big block. Wayne Bushey of NNN was the guy who told me what the problem was. I bought a correct 5 blade from him and problem solved.

Bob
 

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If originality isn't important you may consider a Cadillac fan from the same era.They had big motors, clutch fans, and noisiness was a sin.
 

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No space for a clutch on a BB, long water pump installed in a Nova.
68 Has the space.
 

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Trying to get the biggest volume of air through my big block radiator, I'm trying to figure out which FAN would be better to run. The 7 blade and the 5 blade, both seem to have been available back in 1970 so determining which is best for the big block has me wondering. Would you go with a 18" fan with 7 blades or 5 blade? Why did GM design the difference? I believe the 5 blade design went to Yenko but not sure which is better?
These fans in the thumbnails above are for a clutch configuration due to the large hole center.
The Nova only fan has the small pilot hole.
 

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5 blade no clutch or spacer is correct for factory L78 Nova. I have an aftermarket 18" 7 blade that is load enough to drown out my L78, but my car has never gone over 185°F in stop an go traffic when it 90°+ and I swear it can pull the cars in front of me back lol.
 

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1969 Nova . . 2dr . . Chino Valley,Az USA
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"and I swear it can pull the cars in front of me back lol"


Man ......... that IS funny ..........


'cause , my 250 - 6 ....... had a 7 blade clutch type fan blade (Factory installed - A/C car). I did finally remove it ---- just because I could not find a 6cyl a/c fan "clutch" ...... (I have two of those 7 blade fans).

So, can you get a "fan clutch" rebuilt ? I need to know .....

jim
 

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"and I swear it can pull the cars in front of me back lol"


Man ......... that IS funny ..........


'cause , my 250 - 6 ....... had a 7 blade clutch type fan blade (Factory installed - A/C car). I did finally remove it ---- just because I could not find a 6cyl a/c fan "clutch" ...... (I have two of those 7 blade fans).

So, can you get a "fan clutch" rebuilt ? I need to know .....

jim
I believe you can, check your local Napa.
 
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