Questions about Porsche 911's

[bmwannabe]

Maybe dumb, but how did they get an aircooled engine to work without overheating? Are the engines problematic or reliable? Also, why did it take them until 1997 to figure out that liquid cooled would be the better route? Is there a good source of 911 information out there on the web, pertaining to design/philosophy/technical information/how things work on 911's?

[cramer]

It's called oil.. and lots of it (12 quarts IIRC).... And if you were a true Porsche enthusiast, you'd know only real 911's are air cooled ;) Aftermarket companies have had no problem getting 700hp out of air cooled turbo cars, but for Porsche, water cooled presented a higher reliabilty for added power while also making the engines less noisy.

www.pelicanparts.com has a good tech forum for Porsches.

[Avus_325is]

Even with the ton of oil in them 911's will start to overheat if they sit for too long, like 15 minutes long. My buddy's 25th anniversary 911 cab temp will always start to creep up even if we just stop somewhere and run inside for a few minutes.

[Rob]

The shape of the 911 motor allows good airflow over the cylinders, aiding in cooling. Like Cramer said also, a dry sump oil system, usually with an oil cooler or two help keep temps down. When I had my 911, I always loved how the car would run better @ 90mph than it would in traffic. And again, expanding on Cramer's statement, Porsche had no problem being competitive on the international race circuit using aircooling until the mid 90s, when the thermal limits of the motors started being reached. More stringent noise limits and efficiency requirements in Europe also had a lot to do with the water cooling switch. btw- air cooled 911s sound much better :P

www.rennlist.org is another good forum

[bmwannabe]

idk, i just read that in 1997 they switched to the horizontally opposed 6 cylinder liquid cooled engine as opposed to the air cooled. Im not really a porsche enthusiast, but i want to learn more. Im pretty interested, i love the lines of the bodies on these cars, as well as the efforts of porsche to distance itself from other cars in the way of using different technology. (I.E. Horizontal opposed engines, aircooling, being one of the 1st cars to use turbocharging technology)

[kansas-ix]

The cylinder head design I believe also helps the air cooled 911's stay cool as each cylinder has it's of head like a motorcycle engine head look in appearance, and as stated the 14 quarts of oil doesn't hurt either.

[M3fiftyseven]

I think the change was to conform to the market. Air cooled car engines are a thing of the past. Liquid-cooled is much more efficient, with the only drawback being a slight drag on the motor from the pump.

The 996 still holds about 9-10 quarts of oil, even though it's liquid cooled. The amount of oil capacity was tied less to the fact that the engine was air-cooled, and more to the fact that the oil coolers were in the front of the car, and the engine in the back. Those lines (1 supply and 1 return) hold a lot of oil themselves.

The finned individual cylinder design did most of the cooling at the motor, with the ducted fan at the back (some might say front) of the engine.

I think aerodynamics also played a role in the change from air to liquid-cooled. My 996 has a lot more pans and covers around the engine than my 911 does. Makes the car more slippery by reducing turbulence (thus cooling ability) around the engine.

Oh, and as far as reliability.....I'd say the 911 engine may even be more reliable than the 996. They're pretty much bulletproof.

It's also easier for the engineers to come up with a more efficient HVAC system with liquid cooled systems. It takes FOREVER for the heater in my 911 to function, but only a minute for the one in the 996. People today expect that. Hardcore 911 folks don't give a rat's ass.

[kansas-ix]

Can you drop the 996 engine out in 4hrs like the 911's?

I know that Lotus Esprit turbos had oil coolers up front too, and they don't take near as much oil as 911's.

The old 911 engines are a testament to engineering, bulletproof, easy to remove, air cooled, and easy to rebuild, and light as hell.

[Jon325i]

bmwannabe-

The 1997 car that you are referring to is probably when the Boxster was first introduced. That was the first mass-produced modern "P-car" to employ liquid for cooling instead of just air. It was the motor in this car that served as the platform for all modern horizontally opposed 6 bangers to be developed on. The first of the liquid cooled 911s (chassis code 996) first appeared in late 1998 as 1999 models. The last of the legendary air-cooled 911s was 1998 model car (chassis code 993).

If you want to learn more about Porsche, refer to the Pelican Parts and Rennlist links plus this site

http://www.flat-6.net

Jon

[bmwannabe]

I read a couple things to watch out for on the 911 engines, such as loose cam chain tensioners, as well as faulty head studs due to the cooling issues.... im sure you guys know all that stuff, but you say the engines are bulletproof. Wouldnt bad head studs be a pretty severe problem, i mean driving down the road, and you all of a sudden dont have any compression because your cylinder head popped off..

[DrMcDave]

I read a couple things to watch out for on the 911 engines, such as loose cam chain tensioners, as well as faulty head studs due to the cooling issues.... im sure you guys know all that stuff, but you say the engines are bulletproof. Wouldnt bad head studs be a pretty severe problem, i mean driving down the road, and you all of a sudden dont have any compression because your cylinder head popped off..

thats why the make raceware head studs, 279 dollars plus shipping and you've solved the head stud problem. I have them on my e30, seem to be doing alright, we'll see how they do under boost if i ever get around to buying the rest of the turbo stuff i need.

[BimmerToad]

If properly designed, aircooled have definate potential. Just look at the 2 valve/ cyl horizontally opposed 12 cyl 917 engine. Enzo Ferrari was quoted as saying a 'flat' aircooled 12 would never be competitive and yet the 917 won Le Mans year after year, beating his water cooled 12s of practically the same displacement. And the turbo version of the 917 in the 917/10s and 917/30 was capable of 1400hp! :twisted:

One of the major reasons why Porsche went to water cooled from 97 and on is because it's harder for an air cooled engine to achieve current smog emission levels. Another reason why they went to watercooled is so that they could efficiently cool a 4 valve/cylinder head. IIRC, racing porsches (935, 936, 956, 959, 962) since the late 70s - mid 80's have had water cooled heads, because they've had 4 valve heads. The problem with an aircooled 4 valve head is that as the complexity of the head increases, it's harder to design a streamlined head for the air to efficiently flow past.

As for the head stud problems, stay clear from the '74-'77 911s. Those 911s were the victim of last minute, inefficient smog control which made them run much hotter. On the other hand, since those 2.7 engines didn't last long (~50k mi), the engine has probably been upgraded or replaced.

One day I'll own a '73 2.7 (or 2.8 ) RS or RSR clone :) Nothing quite like a ~300hp engine pushing around a 2200 lb car . . .

As for the 996: I can't believe that with Porsche's history, that car does not have an oil temperature gauge.

[bmwannabe]

Are the bore kits for the 2.7 engines worth it? I mean bumping it up to say 3 liters, what kind of power can they acheive?

[Rob]

thats a tough to answer question, and it really depends on variables such as who is doing the work, what you want to do with the car, etc etc, to make any decision as far as 'worth' it.

[M-technik-3]

bmwannabe-

The 1997 car that you are referring to is probably when the Boxster was first introduced. That was the first mass-produced modern "P-car" to employ liquid for cooling instead of just air. It was the motor in this car that served as the platform for all modern horizontally opposed 6 bangers to be developed on. The first of the liquid cooled 911s (chassis code 996) first appeared in late 1998 as 1999 models. The last of the legendary air-cooled 911s was 1998 model car (chassis code 993).

If you want to learn more about Porsche, refer to the Pelican Parts and Rennlist links plus this site

http://www.flat-6.net

Jon

The first official production flat 6 water cooled for mass market Porsche was das 959

Data from below was borrowed from http://erntheburn.tripod.com/autos/959/9592.htm

Horizontally opposed 6 cylinder, 24-valve DOHC aluminum block and water-cooled heads
Bore and stroke: 3.74" x 2.64"
Displacement:174 cu.in. or 2849cc
Max boost pressure: 14.0 psi
Horsepower: 450@6,500 rpm
Power to weight ratio: 6.6 lbs per horsepower
Compression ratio: 8.3:1
Cd: .31
Fuel system: Bosch Motronic
Induction: Twin sequential turbocharging

Air cooled served it's purpose and can be reliable, but when you say after 15 minutes of idling it gets hot, it's like no Duh? No airflow and why would you let a car idle for 15 minutes as it is a waste of fuel.