930 with Electric Flat Fan ??

[Duckweed Dave]

Hi I'm new to the forum.
I've seen many posts about the pros & cons of flat fans & fan speeds etc. & here's my understanding:
- The flat fan was introduced on the 934 to aid cooling to cylinders 1 & 4 as the cars were involved in endurance racing.
- Porsche run their fans at differing speeds depending on whether the expected use is high RPM racing or lower RPM street use. The High RPM racers counterintuitively run "lower" fan speeds relative to engine speed to maintain an appropriate fan speed when the engine is running faster. Their chosen pulley diameters etc. are chosen as a compromise because its a direct fan drive system & fan speed is directly proportional to engine RPM.

So all this begs the question: "Why not dispense with all the costly & archaic belt drive systems & just use a variable speed electric fan?"

[Jim2]

Cooling is no small task, at full song the fan consumes a few hp. For sake of the exercise lets use a conservative number of 3hp or 2200 watts. With an alternator output of 14 volts you’d need 160 amps.

At 7000 rpm redline the vertical fans spin about 20,000 rpm and moves somewhere in the range of 5000 cfm. There is cooling fan data in the forums somewhere.

[Duckweed Dave]

Thanks Jim,
As always its all to do with power! I'd not realised that the fan consumed so much power.

[kamaro]

In the extreme off-roading, you can't get a better cooling than a good mechanical fan, I'm into sand dune bashing and I see most of the trucks with even the largest electric cooling fans had to stop every hour or so due to over heating, and my v8 FJ40 would dune climb at WOT for many hours with a steady engine temp with a single mechanical fan. Now I heard some good things about the newer brushless electric fans but I'm still not sure about it.

[Bobley]

Mezger said the 917 fan used 17HP and that was "efficient". Electric fans on cars over 600 Watts are rare!