What size 11 blade fan??????

[sean m]

I'm replacing the old, inefficient 5 blade fan on my 77' 911s. Found out there are several sizes of replacement 11 blade fans. Used the search here and found out 1. how and 2. what to measure.
Info from the tech articles:
911 & Year
Fan Pulley Diameter

911 1965-74 3.75"
911 1975-77 3.25"
911SC 1978-79 3.125"
911SC & Carrera 1980-89 3.25"

Using this, I should need the 3.25 fan. When I measured my current 5 blade fan using this method in the photo....it's 3.5!

Now what??? Which is right?

Thanks guys.

Sean

[jstobo]

The fans are all the same size OD. The dimensions are for the pulley size to use with the fan. The smaller the pulley the faster the fan spins, the more air it pushes and the more HP it uses. The 5 blade fan had a smaller diameter pulley than the 11 blade fan so it spun faster. Probably many people when they convert their 5 blade fans to 11 blade keep the 5 blade pulley and that is one reason they see so much better cooling. Hope this helps.

[Bill Verburg]

the production 5 blade fans were 245mm w/ the 3.125" pulley.

When I swapped mine out I used a 245mm fan from a '84-89 Carrera because of the cooling slots for the alternator. Kept the smaller 3.125" pulley.

I don't feel that that made much difference in oil temp., but I am sure that the heads were happier.

[Bill Verburg]

One last thing , the '78-79 used 226mm fans w/ the smaller pulley. You can't use them w/ the other year 245mm shrouds