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Pulley sizes

I just took a 3.0 apart and measured the crank pulley diameter...126mm. For grins I pulled out my pulley stash to see if I had a single pulley (don't need the ac pulley as I live at 8,000 ft and don't need ac) to replace the factory double. The pulley sizes I have range from 116mm to126mm to 134mm. If I raise the diameter, I will increase the fan speed...good for cooling, but do I run the risk of over-running my alternator? I think my voltage regulator protects the battery. I have heard of drilling out the fan hub to use a smaller diameter pulley on top to increase the fan speed, but haven't heard of swapping out the lower pulley. Obviously the fan housing needs to be cleared too, but I haven't heard of different size fan housings for different size crank pulleys. Thoughts?

Speedo
Old 03-14-2010, 06:59 PM
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Lars

The crank alternator pulley sizes range as follows:

1. 2.0 thru 2.4 - 116 mm
2. 2.7 - 131 mm
3. 3.0 SC - 126 mm
4. 3.2 and 3.3 - 127 mm

The factory used the same 245 mm fan and fan pulley for the 2.0 thru early 2.7 motors. This represented about a 13% change in fan/alternator speed for the same engine speed. This variation is small compared to the variation in engine speed over the operating range of the engine.

The early 116 mm single crank pulleys can be used on all later model motors through the 3.2.
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Last edited by tom1394racing; 03-21-2010 at 05:10 PM..
Old 03-21-2010, 11:27 AM
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Lotsa good stuff here---->

5 Blade fan vs. 11 Blade Fan
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Old 03-26-2010, 03:22 PM
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Think I have it figured out...

Spoke with Grady on this subject. Best configuration would be the larger 131mm crank pulley and the smallest 84mm fan pulley. I fortunately have the 84mm fan pulley and my pulley "spares" box turned up a single 131 crank pulley, so I am set. I don't remember what the fan rpm advantage using this pair of pulleys is over the stock configuration...but 1.6 times seems to be what I remember. Now I need to get the pulleys cleaned up and cad plated.
Thanks for all the feedback.

Speedo

Last edited by speedo; 03-26-2010 at 05:35 PM..
Old 03-26-2010, 05:31 PM
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You may have to relieve the cut-out on the bottom of the fan housing by a couple of milimeters. A 131mm pulley wouldn't fit on my 3.0l without a little trim.

Joe
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Old 03-27-2010, 09:10 AM
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oh yeah...forgot to ask

Belt size with a 131mm crank pulley and 84mm fan pulley...what is that? Save me having to guess and corner the market on wrong belt sizes

Thank you...

Speedo
Old 04-17-2010, 05:57 PM
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Quote:
Originally Posted by speedo View Post
Belt size with a 131mm crank pulley and 84mm fan pulley...what is that? Save me having to guess and corner the market on wrong belt sizes

Thank you...

Speedo
I'm bumping an old thread
I just did Lars' conversion with the 131/84

I bought the 725 porsche belt from our host, but its too tight
can anyone please chime in and help me with belt sizes?
I'm guessing at this point...
obviously longer than the 10x725 I tried

Help.....

thanks in advance
brant
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Old 09-06-2015, 08:27 PM
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Since the 131/84 setup is a custom arrangement, I'd be surprised if there is an off the shelf fan belt that will fit with the proper tension
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Old 09-07-2015, 06:46 AM
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I agree. It's unusual and not Porsche

But it's been done before
I'd love to hear what fits from those that have done it ??

I see the Conti (continental) belts come in a 730 and 735mm size
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Old 09-07-2015, 11:22 AM
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And the winning belt size...is?

Conti 10 x 725...and you will likely get to play with the shims. VERY curious to see what temp change you notice Brant.

Speedo
Old 09-07-2015, 11:41 AM
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Was it ever determined if a faster fan has any negative effect on alternator life or the VR?

If you want more cooling there's also Grady's "Rubbermaid solution".
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Old 09-07-2015, 12:05 PM
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I blew 2 of the conti 725's at the race track
Too tight.
One delaminates.
By the way you can't get the right belt n Nebraska on a Sunday!

It did run cooler
But I need a longer belt
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Old 09-07-2015, 02:29 PM
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shims

Where did the six shims end up? Inside the pulley halves and still too tight?
I've got it....put the belts in the oven...heat them up and stretch them or not
You will figure it out. All I can say is the 725 worked for me.
Old 09-07-2015, 05:26 PM
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I've heard that running an 11 blade fan at high speed that air cavitation can occur, causing inefficient cooling (or at least wasted power in turning the fan faster). Has anyone else heard this? If so,any idea at what speed RPM it becomes an issue?

Scott

Last edited by stownsen914; 11-17-2015 at 02:00 PM..
Old 11-17-2015, 01:52 PM
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Cavitation does not occur in air flows. Cavitation occurs in liquid flows only when the local fluid pressure drops low enough to vaporize the flowing fluid.

Running an axial fan, like our five and eleven blade fans, too fast could cause them to stall like an airplane wing stalls on a steep climb. Stall would limit the airflow through the fan. I am not aware of any data showing where our axial fans could stall.
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Old 11-17-2015, 02:29 PM
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I must have forgotten to report back...

Better late than never. I am in thin air at 8100 ft. When I used to drive home from Boulder at 5200 ft, my temps would approach 250 degrees (assuming my sensors and gauges were correct). With the modified pulley setup I rarely get to 220 degrees.
I am very pleased with that lower number....and so is my tired 2.7

Speedo
Old 11-17-2015, 02:47 PM
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Thanks for the update Speedo, and Tom for the correction/explanation.

I thought I'd heard of airflow limitations at high speed for the 11 blade 911 fans. And note that Porsche used the smaller 11 blade fan (226mm?) on its normally aspirated race engines instead of the larger fan. Maybe they had it wrong?

It sounds like the sped up pulley is the way to go at least for a street engine. And from Brant's report, it may well be the way to go on the track too. It's the latter I am most interested in. Has anyone heard of any issue in air flow/cooling with spinning a 245mm 11 blade fan at 8000+ RPM?

Scott
Old 11-18-2015, 10:57 AM
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Bumping this... Is there any new or updated info on this from the guys running the 131/84 combo ?
Doe's it seam to keep the temps low and any belt issues other then what's posted?

TIA
Old 02-13-2018, 07:15 AM
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I've been running this combo for the last 1000 miles or so. No problems or noticeable down side.

OTOH, No obvious reduction in oil temps either. I'm sure it helps, but it is not huge.
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Old 02-13-2018, 07:10 PM
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pulley effect

Since I am the one promoting the strategy...
I have modified everyone of my restos to the smaller/top-larger/lower pulley strategy.
From 2.2 to 2.7 L I have noticed a consistent average temp drop of 20 degrees at my 8000 ft elevation. Air is thin here, and I would think in lower environments where the air is "thicker" that the benefits would be more. Grady always loved to talk about the advantages of water-fan induction which I never attempted. It all started with me wanting to cool an aging 2.7 stock engine without adding a cooler up front ...and I do not have the smog-pump-air injection system on my car, but don't tell any one
Old 02-13-2018, 07:24 PM
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