I have now tried two different fan belt sizes. Both seem way too small. The biggest size I tried was the 10 x 725. Is there a list of sizes of belts for the six-cylinder air cooled engines, I am not sure if it is a different alternator and or different pulleys.

Thank you
MattClick to view attachment

I believe stock is 710. That said there likely is a mismatch of your belt doesn’t fit. You have to either match the pulleys or buy 4 different size belts until you find the right fit.

That’s what I need . A pulley/fan belt conversion chart.
Anyone?

Matt

Once upon a time I saw this discussed on the pelican 911 forums
Not sure if there was a chart or just comments about them

We tested the large pulley in a non oem combination to increase fan speed
Played the belt game a half dozen times
Loving the hole in the firewall

Click to view attachment

And some text I saved a long time ago:
---------------------------------------------
Guys:
There's still some misinformation floating around here ....
the small fan pulleys are 3.125", or 3.25" ( 80 vs 83 mm). Why such small change was ever made we'll never know. Notice that the pulleys are "pulley-halves". You can't simply change the upper fan pulley without also changing the mating fan ( which has the other "pulley-half" surface on it).

From my notes...and this is inconsistently shown in the various parts books, so don't hold me to it, it may be one model year "off":
1965-74/75.. 110 mm crank pulley..95 mm fan pulley
1976-77... 130 crank...83 fan ( may be 80?)
1978-79....130 crank... 80 fan ( or was that 83?)
1980-89.....120 crank....83 fan ( or was that 80?)

for fan sizes / blades / air flow:
1965-74/75....245 mm / 11 blade... 1.3:1 ratio..1390 liters air/sec
1975/76- 77.....245 / 5 blade.......1.8:1 ratio....1265 l/sec
1978-79...........226 / 11 blade ...1.8:1 ratio...1380 l /sec
1980-89.........245 mm / 11 blade...1.67:1 ratio...1500 l/ sec

Turbos used the 245/11/ 1500 set up.

Interestingly... the later curved fans for the 964 were quieter ( by being
curved)...but resulted in lower flow: -- 1.6:1 ratio..1010 l /sec (!).

fan belt sizes:
1965-75....9.5 x 710
1976-77.....9.5 x 725
1978-79....9.5 x 725
1980-on.... 9.5 x 710

There are "borderline" years where these specs don't quite match...and the
goofy 80 vs 83 negligable fan size difference doesn't help to sort this out
either. It won't make a difference in performance but watch out of you mismatch
a 80 and 83 pulley half. BTW....aftermarket will sell 9.5/10x 710 as being
"equal" to 9.5. Don't buy it. There have been reported problems with this. If
possible, buy from dealer or Pelican and ask for the right size.

--Wil
__________________
Wil Ferch
85 Carrera ( gone, but not forgotten )



Early 911 245 mm fan 1.3:1 pulley ratio 1390 ltr/sec @ 6100 rpm
1976-77 five bladed fan 1.8:1 pulley ratio 1265 ltr/sec @ 6000 rpm
1978-79 226 mm fan with 1.81:1 pulley ratio 1380 ltr/sec @ 6000 rpm
Turbo fan 1.68:1 pulley ratio 1500 ltr/sec @ 6000 rpm
964 fan 1.6:1 pulley ratio 1010 ltr/sec @ 6100 rpm
New twin turbo 1.8:1 pulley ratio 1210 ltr/sec @ 6100 rpm


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.
__________________
Tom Butler
1973 RSR Clone

Wrap a string around the setup & measure it's length.

Thank you

Will do, thanks

The old standard 911 belt sizes were 9.5 x 710 or 9.5 x 725
On my 911 SC engine for some reason a 735 or 740 seems necessary

I think I’m going to get a few belt sizes tomorrow. My SC engine used 710 or 725. I am going to measure the pulleys tonight and post.

Matt

oops