Sunday, 14 October 2012 14:43
Whenever you read an article about the 911, you always get the complaint about the engine being in the wrong place, and until 1999, air cooling? Whats that all about?. Conventional thinking is very powerful. If you look at the facts, rear/mid engine air cooling ( REAC for short) as prescribed by old Dr Porsch is the most perfect configuration for a passenger car. Lets look at the at the advantages of air cooling. Fast warm up: air cooling has low thermal mass. Note when you stand near a 911 starting from cold, how fast warm air comes from under the car. Heating: We can blame Volkswagen for the myth of poor heaters. The heater on my 59 beetle put out as much heat as a gnat’s breath (plagiarism note: I read this phrase somewhere). The exhaust stoves on a 911 are not much different that the furnace in your house, ie, hot toxic gases warming up a fresh air stream. My SC’s heater puts out prodigious amounts of heat, and almost instantly. Porsche deserves some brickbats here though. It took till the 964 in ’89 for them to figure out to regulate the heat automatically using dash mounted controls. Air conditioning load: a water cooled car with the rad in the front, bathes in its own thermal pollution. Simplicity: No rad to corrode, rad hoses to pop, water pumps to squeal, head gaskets to leak glycol into the oil or cooling jackets to freeze. Lets face it, water and engines are not really compatible. Reminds of the small rad leak I had in Italy. A well meaning East German trucker came by with some epoxy and I put my finger right through the rad. On the DVP in heavy traffic I once didn’t notice that my cooling fan had failed until a mixture of oil and antifreeze exploded out from the coolant expansion tank after the temperature gauge went off scale. Do fan/serpentine belts as used to power the 911 fan fail – yes, but I’ve never experienced it myself or had it happen to anyone I know. My 914 has the fan connected directly to the crank.
Are there any advantages for water cooling? Aerodynamics: This used to be an advantage for REAC. Back in the day, I remember reading about how the lack of rad airflow resulted in a 20% improvement in aerodynamics for air cooled cars. That however, was in the days when wind tunnel testing was done by a guy with a fan and a cigarette. Today, they can feed the rad by bleeding off a bit of air here and there. To provide sufficient airflow for REAC to reduce the power consumed by the engine fan would be very difficult. Power density/pollution control. It’s easier to control temperatures and conduct heat from hot surfaces with water, but in my opinion this is just an engineering problem. At about the time of the 959, Porsche said they could not do 4 valves per cylinder with air cooling. I however, have a 1993 air cooled motorcycle with 130hp out of 1.2 litres and 4 valves.
So why did Porsche abandon air cooling? I’m guessing it was that all the old guys had retired and/or died and they took the easy way out. Even I, in 1985 bought a new motorcycle simply because it had water cooling. Now I know better.