porsche fan

hi anyone give me some advice on how fast i should spin my 12 blade fan on a type 4?

as slow as you can, the air output of the 12 blade is too much and can actually make back pressure cause of air stagnating in the shroud as it can't get past the heads and cylinders, this page has info on pulley sizes for 911 kits http://www.aircooledtechnology.com/cooling/index2.shtml

Have a good read, hope i helped you, Damo.

this page has info on pulley sizes for 911 kits http://www.aircooledtechnology.com/cooling/index2.shtml

Have a good read, hope i helped you, Damo.

I could not find that info, only info to use the sellers own system...

66deluxe wrote:as slow as you can, the air output of the 12 blade is too much and can actually make back pressure cause of air stagnating in the shroud as it can't get past the heads and cylinders,...

According to the facts ('Jake-speak' for you), the original 12-blade flows less than all others. Key also is the drive ratio as you can see from the list below from a french guy that collected all factory specs:

Early 911 245 mm fan with 1.3: 1 pulley ratio 1390 ltr/sec @ 6100 rpm

1976-77 five bladed fan with 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 with 1.68:1 pulley ratio 1500 ltr/sec @ 6000 rpm

964 fan with 1.6:1 pulley ratio 1010 ltr/sec @ 6100 rpm

New twin turbo with 1.8:1 pulley ratio 1210 ltr/sec @ 6100 rpm.

Early 911 245 mm fan with 1.3: 1 pulley ratio 1390 ltr/sec @ 6100 rpm[/color][/b]


..................diameter (mm).........rpm.........pulley ratio....speed (ft/sec)

early 911................245..............6100............1.3 ..............334

76-77 5 blade..........245..............6100............1.8...............462

SC.......... ...............226..............6100............1.8...............426
.
930..........................245.............6100...........1.68...............431

964/993................... 279.............6100............1.6...............468

993tt.........................279.............6100............1.8...............526


1965-74/75...... 110 mm crank..................95 mm fan pulley
1976-77... ........130 mm crank..................83 mm fan pulley
1978-79............130 mm crank... ..............80 mm fan pulley
1980-89............120 mm crank..................83 mm fan pulley

fan sizes / blades / air flow:

1965-74/75........245 mm / 11 pales.........1.3:1 ratio..1390 liters air/sec
1975/76- 77......245 / 5 pales..................1.8:1 ratio....1265 l/sec
1978-79............226 / 11 blade, pales ...............1.8:1 ratio...1380 l /sec
1980-89............245 mm / 11 blade.........1.67:1 ratio...1500 l/ sec
964...............279mm / 12 blade......... 1.6:1 ratio..1010 l /sec (!)

BTW, it also stated that the 12-blade fan only uses 8,1 hp at 6100 tpm!
(but has much more directional vanes inside the housing)

FYI, that is less hp-usage than a type 1 fan at that rpm!... (another myth bustet)

brilliant thanks you are welcome at my place any time for a drink or ten once again thanks!!!!