Wrong diameter fan pulley

[pjv911]

I UPDATED THE 5 BLADE FAN ON MY 2.7 WHEN IT WAS REBUILT TO A 11 BLADE 245MM(?) UNIT. IM STILL USING THE 5 BLADE PULLEY AND IT SOUNDS LIKE A FIGHTER JET EVEN WHEN IDLING. IS THIS THE WRONG DIAMETER FOR THE 11 BLADE ? WILL I ALSO IMPROVE MY HORSPOWER TO THE WHEELS WHEN I GET THE CORRECT SIZE ?

Kurt Williams

[Chuck Moreland]

The answer is... it depends.

The 5 blade from 76 to 77 spins at 1.8:1.

The early 11 blade 245 mm from 68 to 75 spins slower at 1.3:1 ratio.

The later 11 blade 245 mm from 78 to 79 was the same as the 5 blade, 1.8:1.

The latest 11 blade 245 mm from 80 on spins slower at 1.67:1.

Other than the drive ratio, I believe all those 11 blade fans are the same (but I don't know this for sure). So the question is how much cooling you want.

Spin it slower and you will bump HP. There was an earlier thread that said just lengthing the fan belt can be good for up to 7 HP. Lengthing the belt reduces the ratio since the belt rides higher on the split pulley.

[pjv911]

My engine is a 77` so I gather I should call the dealer for the early pulley. BTW the heating system blows with unbelievable force similar to a leaf blower when the car is revving high. I kinda like the turbine engine sound and it definetely draws attention since its so loud .

[Bill Verburg]

• -75 1.3 245mm except for some racing models which had 226mm
• 76/77 911 & Carrera 3.0 1.8 245mm 930 1.67 245mm
• 78/79 911 1.67 226mm 9301.67 245mm
• 80-87 SC/Carrera 1.67 245mm 930 1.8 245mm

I used the stock 76 Carrera 3.0 pulley with an 11 blade 245mm fan and had no problems with noise or heat, there was a good flow of heated air but not to excess.

The fan uses ~6 hp at wot, much of that going to the alternator, so if you underdrive at 1.3 and put in a small alternator and backdate to the smallest 226mm fan(and shroud ala RSR) ypu will gain less than that in terms of hp

[alan911]

Just curious...... on a '77 2.7. Where are the measuments of the pully taken from Exactly, (i.e., where to put the caliper) and, I take it the ratio is the the fan pulley vs crank pulley ?

I went from the stock 5 to the 11 about 12 yrs ago and the first thing I noticed was that on start-up, I had to initially rev the engine to about 1500 rpm before the the V-regulator would trip and the red light would go out. It didn't do this with the old 5 blade.

I kept the pulley half from the old 5 blade and used it on the 11.

What I'd like to do is get more revs from the fan end for more cooling and better alt. output at lower RMP. What to do ??

[Bill Verburg]

For more revs of the fan you need a smaller fan pulley, the stock 5 blade pulley is the smallest normally available with the 1.8:1 ratio. Porsche already sped up the fan for the reason you gave, more juice from the alternator at lower speeds. It sounds like the alternator/voltage regulator may be the issue on your car

[alan911]

I suspect you're right. Going to have it checked tomorro.

thanks.