11 Blade fan

stevo96 · stevo96's Garage

Hi All,

I need to do this upgrade ASAP - Ive seen a few 11 blades for sale, my question is - can i just buy the fan and do a direct replace for my 5 blade or do I need to buy a different housing / pulletys etc?? The engine is a 2.7i.
Thanks!

faverymi · 08-07-2011, 04:48 PM

I did a direct replacement with an 11 blade fan that I got in the forum.
I had the right pulley.
Housing was the same.
Getting the old fan out of the alternator shaft was a *****.
Take pics of the wiring. Can be another problem

Talk to Tom1394racing in the forum. He will have the part at a good price

Flat6pac · 08-07-2011, 04:54 PM

The 5 blade fan has the 12 small holes near the center. This represents the pulley taper and size needed. 77 uses a 725x9.5 belt because of the crank pulley. For replacement use 1980 on fan, even Carrera will fit and be correct.
Bruce

stevo96 · stevo96's Garage

Hi, apologies but why use the 1980 fan onwards - will the ones before that not fit? I've seen one for sale on ebay which states it fits all cars from 68 - 79, is that right? If I buy the wrong one can it be made to fit?

Targalid · 08-07-2011, 09:56 PM

I just did the upgrade. You need the 245 mm 11 blade fan. Two years of the 911 SC had a different diameter and you don't want those years' fan. I believe it was 80 and 81. Any other year will fit. It has to be 245 mm. The pulley for the five blade fan actually turns the fan faster than the standard 911. I saw a post that said it was the same pulley ratio used to cool the Turbo models, 1.8 to 1. Anyway, my 11 blade fan sounds like a low flying spacecraft. The engine is cooler than with the 5 blade fan by about 20 degrees F. To change the fan, you need to remove the pulley, loosen the fan housing and tip it up at an angle to clear the sheet metal at the back of the engine. Unlike what the book says, you do not have to take off the alternator. Then you can put a 3 jaw puller onto the 5 blade fan at the edge of the fan hub between the fan blades, put the nut back onto the shaft so that the center of the puller does not slide off to the side. Then just turn the bolt on the puller and the fan will pull off.

stevo96 · stevo96's Garage

Thanks targalid! I don't have one of those pulley things so I guess I'll have to remove the alternator.... Thanks again.

dhagood · dhagood's Garage

you can buy generic pulley/gear pullers on ebay for under 20 bucks. you can also rent them buy the hour at any number of tool rental places.

Flat6pac · 08-08-2011, 02:50 AM

The smaller fan was from 78/79 SC. The replacement info I gave is good.
Bruce

Targalid · 08-08-2011, 06:49 AM

Stevo,
You will still need a puller to get the fan off the alternator. I did. Don't try to pound it off as you can damage the alternator bearings. As dhagood says, rent a tool if you have to. I bought a complete set of pullers at Harbor Freight for around $20. Are they cheap? Yes. Are they as good as American made tools? No. Do they get the job done? Yes.

stevo96 · stevo96's Garage

Attempted to take the fan off tonight which is a huge deal for someone who only knows how to use a hammer....
I followed the instructions in the tech section which all rang true until I tried to pull the housing out. Mine had a plastic cowling on the back with about 6 nuts which were an absolute pain to get off - I have the red knuckles to prove it. I also had to disconnect an earth wire attached to the final nut which was the hardest to reach, I got there in the end....
I accidently dropped one of the small nuts into the back of the alternator - can't get it out, I'm thinking its magnetised.....?
The housing came off ok with a bit of force and so did the fan eventually.
The 11 blade is on order - hopefully I can get it back together ok!

Targalid · 08-09-2011, 06:29 AM

The plastic air deflector, as well as the 11 blade fan upgrade, is detailed in Wayne Dempsey's book "101 Projects for your Porsche 911". If you don't have that book, you should order it from Pelican. Be careful during reassembly that you don't overtighten the nuts against the plastic and crush it.

Flieger · Flieger's Garage

The plastic air deflector is not an upgrade. Every engine is supposed to have it. The 5 blade fan was only there to make the engine run hot to reduce unburned hydrocarbon emissions in slow speed US driving. They were intended to have 11 blade fans.

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by Flieger

The plastic air deflector is not an upgrade. Every engine is supposed to have it. The 5 blade fan was only there to make the engine run hot to reduce unburned hydrocarbon emissions in slow speed US driving. They were intended to have 11 blade fans.

The 245mm x5 blade fan was used to step up alternator speed at idle it was accompanied by a change in pulley size

blower drive ratio before '76 5 blade was 1.3, these fans move ~1390 l/s @ 6k rpm

for '76/77 w/ 5 blade w/ 1.8 blower ratio is used, 1265 l/s @6K rpm

the '78/79 use the small 226mm x11 blade fan w/ a drive ratio of 1.8, these move 1380 l/s @6k rpm

from '80 245mm x11 blades are used w/ a drive ratio of 1.68, 1500 l/s @ 6k rpm

the '84-89 11 blade is the best retro fit as it also has alternator cooling slots, these work fine w/ the stock '76/77 pulley halves.
summary

stevo96 · stevo96's Garage

Thanks Bill. Ill take the housing, fan, alternator and pulley to the guys house who's selling the fan to make sure it all fits. The fitment of the fan onto the housing/alternator didnt change did it?

stevo96 · stevo96's Garage

Targalid - what size was your pulley on the 5 blade fan?

Quote:

Originally Posted by Targalid

I just did the upgrade. You need the 245 mm 11 blade fan. Two years of the 911 SC had a different diameter and you don't want those years' fan. I believe it was 80 and 81. Any other year will fit. It has to be 245 mm. The pulley for the five blade fan actually turns the fan faster than the standard 911. I saw a post that said it was the same pulley ratio used to cool the Turbo models, 1.8 to 1. Anyway, my 11 blade fan sounds like a low flying spacecraft. The engine is cooler than with the 5 blade fan by about 20 degrees F. To change the fan, you need to remove the pulley, loosen the fan housing and tip it up at an angle to clear the sheet metal at the back of the engine. Unlike what the book says, you do not have to take off the alternator. Then you can put a 3 jaw puller onto the 5 blade fan at the edge of the fan hub between the fan blades, put the nut back onto the shaft so that the center of the puller does not slide off to the side. Then just turn the bolt on the puller and the fan will pull off.