WTB - 1978 911SC small diameter fan

[sezme]

1978 911SC small diameter alternator fan needed. NO chips or damage please! Measures 9 inches tip to tip...

Stu
sezme@aol.com

[andyjboy]

Stu - there's a 225mm fan & housing on pelican:

http://forums.pelicanparts.com/showthread.php?t=452296

[sezme]

Andy -

Thanks. I've sent him a PM to see if he'll just sell the fan. Crawford is making my ring....

[porscheaparts]

does anybody know what the advantage could (would) be of this smaller fan ?
less friction, more power ???
thanks

[andyjboy]

Porsche used a smaller (226mm) 11-blade fan on all its 911-based racing cars (911R/ST/RSR etc) - the thinking behind it being that since these cars would spend most of their time running at high revs, then the std 245mm fan would produce too much cooling air causing the engines to run below optimum operating temperature.

[J-P]

Engine fans, direct-drive airplane propellers...same concept.

The bigger the propeller you have to turn, or in this case, the bigger the fan being driven off the crankshaft, the more power you are going to pull from the engine to drive it, thus less power available to propel the car.

It seems miniscule, but in big-dollar racing, it is one more piece to the victory puzzle. This gives the car that much more available power.

I don't think Porsche was worried about over-cooling. Rather, it's the other way around. They figured a smaller fan turning at higher speed would still provide enough cooling air despite the decrease in overall air volume for a given engine RPM.

[letsrollbabe]

The race engines Porsche used the smaller fan on typically did not have an engine mounted oil cooler (used grenade filter instead), and thus no air channel to an oil cooler, thus the volume of air produced more turbulence. I remember reading somewhere that the smaller fans consumed up to 8-9 hp less at 8000 rpm.

[porscheaparts]

Thanks for all this info.
Can I conclude that I can put a smaller fan which will cool my engine enough and maybe I'll gain a little horse power ...
I have a 3 L SC engine with about 240 HP
Regards

[sezme]

Bingo (but at the risk of overheating in a daily driver)

[lisa_spyder]

Stu,

Funny thing - going through some bits and pieces this morning for someone else and found a small fan .

Can send you some pics if you are still in need of one.

Cheers,

Lisa