Hi everybody,
i am looking for the dimension of the cooling blower pulleys or the transmissionrate of a 2,2 six.

Thanks in advance

Anderson says 1,3:1 ratio (Spec book says "approx 1,4:1" which I figure assumes zero slip...) all 911 from 1968 to 1975 displacing 1380 liters/sec @6500 crank rpm.

several pulleys - crank and fan - used through the years that can be mixed and matched to produce a fairly wide variety of drive ratios.

Thanks for the information, but i feared that answer! I have a little uncommon setup with a 2,2 engine and a turbo blower (i think,because the part number starts with 930...). The crank pulley is somewhat 12cm and the blower pulley is 10cm.

So this is 1,2:1, much to low in my opinion.

Should look for another setup.

well - it's not the ratio of the diameters that makes the drive ratio, it's the ratio of the circumferences...

but you should know that the hot setup on lots of short (66mm) stroke race engines is the 5-blade US fan - much less HP loss and still pumps plenty of air at high engine speeds. in the US '74-'75 cars, that was used with a crank pulley that produced a 1,8:1 ratio. this was the plan for my 2,2E, before I sold it, and I'll probably use it on the 2,8. spins the alternator faster too, for better power output.

most factory race engines used the 1,3:1 ratio, but a smaller (226mm vs road car 245mm) fan and shroud. again - less HP loss, and less rotational inertia - that's from the 906 through the 956/962 - although of course those last two had water-cooled heads.

Turbos and 1980 and newer 911's used a 1,67:1 ratio (that's pre-993, perhaps pre-964 - I don't follow the newer cars as closely).

So - IMO - first you need to compare the ratio of the circumferences, then you need to mount a CHT, before deciding you need to make too many changes.

which, of course, still gives you a ratio of 1.2:1 ...
Andy

PS: Math 1 on 1 on a monday morning

circumference = 2 * Radius * Pi = diameter * Pi

meaning, that if you multiply both diameters with Pi to get the circumference you can simply ignore the constant (Pi) and get the same ratio result by just using the diameters.
both calculations return 1.2 as a result ...

yeah - I knew the constant factored out...

If we take the factory 1,3:1 number, I still remain unconvinced 1,2:1 is that much less, but then it isn't my engine... I don't know if the crankshaft pulleys are interchangeable between the 66mm stroke and the Turbo's (which was just 70,4mm in the early years) but if so, using the Turbo pulley should get back the 1,67:1 ratio.

Mike -as promised here are the sizes of both crank and fan pulleys on my 2.4
(I've measured outside diameter as the belt is in the way + the top pulley 'vally' is adjusted by adding removing shims + the outside should be enough to work out the ratio)

Is that 1.2:1? not sure how to work out ratios

115.36 / 95.88 = 1.2031706299541093032957863996662

so yes, that's 1.2:1 ...
Andy

Hi James, thank you very much !!
But now i am a little bit confused. 1,2:1 seams to be the genuine ratio for a 2,4 or a 2,2. Where does the 1,3:1 ratio come from??
Maybe my setup isn´t so wrong? I was able to find a crank pulley with 13,5 cm. I will give it a try.



oh by the way, today arrived the factory engine tin. Looks very nice. Will post pics in the got the six -thread.

Anderson.
Porsche Little Spec Book says 1,4
of course the "correct" measurement needs to be made where the belt contact point actually is - it can be fairly deep in the fan pulley to achieve a higher effective drive ratio.