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Join Date: Oct 2006
Location: Chas, SC
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Increasing Fan Speed

Just read in Bruce Anderson's latest 911 Performance Handbook that he recommends using a crank pulley from a 76-77 on the 930's to speed up the fan in order to increase the cooling. Anyone tried this?
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Tim
1986 930
Gone:71,2,4 914's, 70T, 71T(RS),77S
Old 02-10-2007, 06:35 PM
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Location: Orange, CT
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I have not tried it but I want to as I am going to run a bunch of power on stock 930 cylinders. Does he say anything about the belt size?
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Kris
86' 930/GT-40R Sold
94' Rustang GT daily
Old 02-12-2007, 07:22 PM
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No, just the pulley.
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Tim
1986 930
Gone:71,2,4 914's, 70T, 71T(RS),77S
Old 02-13-2007, 04:07 AM
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I have some limited expirience with increased fan speed on aproject I worked with. We increased fan gearing on turbo-converted 3.6 N/A engine to 2.41. At 7000 RPM, fan was spinning @ 16900 RPM and severe belt problems appeared. Generator inertia was too big and it was tearing the belt apart. Fan tip speed @ 7000 RPM was aproaching M 0.66. We sourced problems to the fact that rapid RPM changes made heavy OEM generator accellerate/deccellerate too quickly which teared up the belt in zero time. Also, car wore out the generators quickly.

You can see the flat belt, belt-tensioner (actually a 944 cam belt tensioner) and "outsourced" generator situated on the right side of the fan here:


It was finally solved by using flat belt and fitting lighter generator situated out of the fan and driven by separate belt with lower gearing. I believe biggest problem with severely turbocharged aircooled engines isn't so much cylinder temperature as it is head temperature.

Also, curved 3.6 N/A fan flows less air than "930-style" straight-bladed fan. It's quieter though.

I strongly suggest checking belt wearing issues if deciding to gear up the fan. OEM V-belt is just capable of default gearing and might fail if subjected to up-geared fan.
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Thank you for your time,

Last edited by beepbeep; 02-13-2007 at 07:13 AM..
Old 02-13-2007, 05:53 AM
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