951Porschiste

Greetings from a watercooler,

My 13 year-old son needs to do some research on different types of combustion engines. I would like to find out what was the original thinking behind choosing an air-oil cooled design versus a watercooled design. In other words, why did Dr. Porsche go with an air-cooled design originally and what are the advantages (and disadvantages) of the more modern (pre-996) air-cooled engines.

Thanks in advance.

rzepko6194

Aircooled advantages: no coolant, radiator, hoses etc.

Aircooled disadvantages: more noise (but music to me)

John

StanV

Bonjour Andre,

I'm sure others more worth listening to will weigh in with their opinions, but to my knowledge the major advantage was the lighter weight of the air-cooled motor. This would be especially important when the engine is in the "right location", hung out behind the rear axle. The lack of water jackets acting as sound insulators also makes for a better-sounding motor, although I'm not sure this was factored in (no marketing dept. back then).
As far as disadvantages, I am not so sure. I believe that air-cooled engines have a wider range of operating temperatures, so cannot run tolerances as close as liquid-cooled motors.
The Porsche history books that I own don't really address this, but I'm sure your son will get references from other list members regarding sources to check.
Wish I had that project when I was 13!

Stan V

dial911

Given proper engineering, air-cooling works very well on all kinds of engines.

I think one of the main advantages is it's inherent simplicity, in operation, as well as production.

The good Doktor seems to have planted the air-cooled seed, deep in the German industrial psyche. To this day, the Germans produce some very fine air-cooled Diesel motors, of large displacement and output.

Bill Gregory

Andre,

I went back to look at two sources and didn't find what I wanted. Somewhere, there is discussion on the merits in the 1930's of air-cooled engines. I want to say that ease of maintenance and simplicity influenced the air-cooled choice. Looking at Karl Ludvigsen's "Battle for the Beetle" and Ferry Porsche's "Cars Are My Life", they say the initial suggestion for the people's car was made by Hitler as a 3 cylinder air-cooled diesel, front mounted. In Porsche's book, he says "The question of the engine had been decided only shortly beforehand [referencing building the first two prototypes]. We had studied various units, including two- and four-stroke engine, two- and four-cylinder engines, and in-line and flat opposed-engines. We eventually settled on an air-cooled flat four with a cubic capacity of 985cc and overhead valves, which produced 23.5 hp at 3,000 rpm."

951Porschiste

Thanks all for these initial responses. Keep 'em coming.

I'd also like to know why Porsche went to water cooling for the 996. I've read somewhere that they had reached the maximum power output of the flat-six air-cooled engine with the 993 and that to get any more power they had to go to water cooling. Anyone know why that would be?

Also, is air the only cooling agent for the older Porsches or are these engines really cooled by oil which is itself cooled by air?

Again Thanks in advance

Speedraser

As I understand it, the supposed reasons for the change to water in the 996 was because they didn't think they could continue to meet coming emissions and drive-by noise standards. Since the 993 engines are pretty clean, many people think the real reason was the drive-by noise issue (water jackets are good sound insulators) more than emissions. However, Porsche wanted to use 4-valve heads, and they say they never could get 4-valve air-cooled heads to cool properly. This is why many of the race cars and the 959 had air-cooled cylinders and water-cooled heads.

The air-cooled engines are often considered air and oil-cooled.

dial911

Of course, air-cooling is actually a misnomer. The engines are cooled by both air and oil.

GrantG

"Aircooled advantages: no coolant, radiator, hoses etc. "

Also no water pump water thermostat

gerry100

The History channel "Automobiles" series VW segment says that air cooling was chosen because most Germans did not have garages and frezzing up would be an issue. Of course, Porsche got his start w VW parts for his initial designs.

hoffman912

that same history channel episode said that since it didnt have radiators/water cooled, it wouldnt boil over when driving up the alps, and their high altitudes.

air cools the oil. oil cools the motor.

art

I always assumed it was for ease of manufacturing, (no water passages to cast). Aircraft engines from Prof Porsche's time were air coooled for obvious reasons, so the leap to cars was not huge. Other cars were air cooled, Franklin in the USA.

Also the crank case is simple in terms of casting and machining. The downside to the simple machining is all of the leak paths that have to be dealt with.

Art

DGlenn

I was going to post the same info until I saw you had already posted it.

dial911

I don't buy into the History Channel rational at all.

Reading through Ludvigsen's "Excellence Was Expected", I could not find any references to frozen temperatures, and lack of garages etc.

More like....when you are trying to build a car in a remote, poorly-equipped, sawmill, you will go with what's expedient and simple (air-cooling).

jchaley

I think that the change for the 996 engine with water cooling were two fold. They could go to 4 valve head and maybe more important is they could design a much less expensive engine. A replacement 993 engine was around 25K and the 996 engines are around 8K. For the high perfomace 996 cars (GT3, GT2, and Turbo) still use the old case and internals from the air cooled cars.

john