dvkk

The choice of aircooling has nothing to do with the Porsche automobile. It goes way back to the early 1930s when Porsche Sr. was developing the VW. At that time, the vast majority of Germans did not own a car, so they didn't have garages. Its been well documented in VW history books that aircooling was chosen since most cars would be left outside all night. Many of the original design features of the VW were outlined by Hitler, including this one. One of Hitler's "election" promises was to put a VW in the hands of every working German, few of whom had garages.

The development of the VW was financially backed by Hitler's **** government, who had deep pockets. Porsche's villa in Stuttgart was hardly a "remote, poorly-equipped, sawmill" Rear engine, transaxles, magnesium engine cases and air cooling was considered to be state of the art at that time. The fact that his design continued production for 70 years proves this.

uli953

"Air can´t boil and can´t freeze"

That´s what Mr. Porsche sen. said.....

Petevb

No one has mentioned some inherent disadvantages of air cooling- somewhat limited specific output and efficiency. Because the heads of the 911 can’t be cooled as well as a water cooled design they get somewhat hotter, all things being equal. This lowers the detonation limit, and requires you to run either slightly less boost or compression compared to an equivalent water cooled design. This would be why the factory went to water cooled heads for endurance racers in the ‘80s (you can see how these disadvantages would be particularly important where there is a displacement cap). Efficiency drops slightly with the lower compression. Because you can make similar power with a smaller water cooled motor the apparent weight advantage of the air cooled motor is offset. Witness the late 993 vs early 996 motor.

r911

Air simply doesn't transfer heat very well as a working fluid (often leading to the claim that air doesn't "cool very well" which is a bit off).

Valves run hot due to the combustion gases and are thin (as they must allow gas passage and be light to close and open quickly). Add these up and you need good cooling. More valves allows more holes for gas flow, thus more power. But PAG could not make an air cooled head with enough room to allow air cooling, hence the requirement that they move to water. With that, the daces long air-cooled primativism was ended and PAG was able to use a modern engine head design like everyone else.

Noise shielding and pollution issues are also involved -- but they could have stuck with lower output motors and solved those problems.

951Porschiste

Thnaks very much all for your insightful responses. I'm actually beginning to warm up (pardon the pun!) to the idea of getting a pre-996 911 as a next P-car!

abe

It had to do more with the military under **** Germany wanting auto/tanks to run on air cooled engines
in the desert.
abe

Daniel Dudley

Of course the reason that liquids cool more efficiently than gasses is because the molecules are so much more densely packed together. Heat is the energy held by molecules, expressed by the speed at which the molecules bounce around. As a gas, the molecules literally fly around. As a liquid, they tend to be so densely packed that the movement is more like vibration, but the point is that there are a lot more molecules to transfer energy to in a liquid. Radiators of course work by transfering the heat of a liquid to air by creating a large surface area for the air to pass over, increasing the number of molecules that can pick up energy. This is also the reason that air cooled engines have fins.

Also, consider that the energy is transfered in much the same way that a pool ball bounces off another pool ball. A well shot pool ball will often transfer all of it's energy to the ball it strikes. Molecules flying around like pool *****. The speed that they fly at is heat, and the striking of one molecule against another is the transfer. Lets ignore radiational heat for this discussion, like wave energy, light or glowing heat. But consider a red hot bar of iron in the air, slowly cooling. Now dip the Iron bar into some water. Lots of heat transfer very suddenly, yes ? This is in fact why many refer to Porsche engines as oil cooled, and why they have radiators for the oil.

Thanks for the topic. I haven't thought about that for years

DanS911

Nice......why is such talk of air cooled motors like music to my ears?