air cooled vs water cooled - is it important?

[Bailey]

I know many Porsche purists cringe at the thought of a water cooled Porsche. I myself am a traditionalist (they were air cooled for so long), and I also like the lines of the older cars better. My question is, why did Porsche switch? If there is better cooling with water, why didn't they do it long before? Also, didn't many of their race cars in the past employ water cooling? Given this history (if correct), does it make water cooled Porsches more palatable. I honestly don't know much about the engines and cooling and their different pros and cons. I have found myself gravitating towards certain models based more on styling. As Porsche made the switch to water cooling I feel they started designing cars that might appeal to a wider audience, that incorporated more creature comforts, and that are perhaps easier to drive, losing some of the old Porsche appeal.

[ChrisBennet]

Water cooling is just a great way to cool a motor. Porsche race cars had water cooled heads 20 years ago. I think they waited so long because they are a small company and couldn't afford to make big changes like that until they absolutely had to. Look at the 911 Turbo; that didn't have electronic fuel injection until 1996, 12 years after the Carrera.
-Chris

[304065]

As a heat transfer medium, water is many, many times more efficient than air.

As specific output of Porsche racing engines increased, so did the heat generated in the combustion chamber, that was absorbed by the head, which was then cooled by air. The trouble is, when they did the later 935 with four-valve heads, there wasn't enough material in the head to be an effective heat sink. Therefore, they were approaching the "materials limit" of the aluminum head- it was getting too hot to function properly. Hence the water-cooled heads of the 962.

If you look at the specific output of the production engines, however, it's not that high: the 2.0 S of 1966 had 80 bhp/liter, the 993 had 76.3. So air-cooling worked all right. Enter the turbo, however, and it's a whole other ball game.

Also, emissions was a factor: an aircooled cylinder is not as dimensionally stable as a water-cooled one, requiring you to run higher tolerances, which allow more oil through, resulting in higher emissions. As emissions regs got stricter, that was the end of air cooling.

[beepbeep]

Watercooling is superior in many ways. It allows usage of 4-valve per cylinder, controlls thermal expansion much better and allows usage of monolithic heads.

Porsche knew this long time ago.

[mperkins]

Thanks, Bailey, this is actually a great question and I hope this thread elicits further feedback.

I've always been interested in why Porsche stuck w/ air cooled engines (in their passenger cars) for so long..
Have never been able to find well researched answers.

In other words, what was the 'reasoning' and 'advantage' over water-cooling??

[JMar]

Hmm if I'm not mistaken Porsche started water cooling in production engines back in the 70's...it was only the 911 variants that remained air cooled.

[KobaltBlau]

* simpler
* lighter

[mperkins]

yes, exactly - only for the "911 variants" obviously.

as Goran stated, Porsche knew the benefits of water-cooling way before the 1970's.

[rob justice]

Also I believe noise was another reason - a water cooled engine is quieter than an air cooled.

[jazzbass]

Here's what I've heard from various people/websites, all of which is subject to correction by those who actually know what they're talking about. Air cooling was a *60's* thing. By the early 70s, Porsche knew water cooling was the way to go. Furman thought the 911 was dead, and the 924 and 928 projects were the replacements. But the 911 kept on selling, despite little to no development effort on it until the late 80s (why didn't we get a good shifting transmission until '87?). So Porsche wanted to all water 30 years ago. Fortunately for us, people kept buying those darn air cooled 911s.

As for racing, I've heard they wanted to go water cooled as early as the 917, but they couldn't becuase of a contractual agreement with VW. Apparently Porsche was getting sponsor money from VW, and VW wanted an air-cooled race car, since they're whole product line at the time was air cooled (Bug, Bus, Type 4s). I read this on some random website devoted to LeMans and have no idea if this is true or not.

For now, however, I think the "water-cooled" stigma you see on this board comes a lot from the (IMO) bland styling of the 996. If they would have stuck the 996 engine in a 993, things would probably be different. Oh - they'd need to keep the dry sump, too. No 911 should have a wet sump engine.

[vesnyder]

I do not base this on fact, but with the introduction of the 944 and 928 (water cooled), Porsche considered discontinuing the 911. As the change in leadership at Porsche reconsidered, the decision was made in teh late 80's to maintain the 911, and that was when the decision to replace the air cooled 911 motor with water cooled. This coupled with the stricter emission requirements drove the movement to water pumpers? Make sense?

[klaucke]

I read in a book on classic sports cars that the 928 was supposed to be the successor to the 911, and they would then make the switch, tentatively, to water cooling. However, as previously stated in this thread, the aircooled 911 kept selling, so they didn't end production.

[88911coupe]

I have heard also that the new engine control systems require very narrow operating temps and air cooling makes it difficult to keep the temps in this range. Not sure where I heard that though....

[KobaltBlau]

Originally posted by rob justice
Also I believe noise was another reason - a water cooled engine is quieter than an air cooled.

Absolutely. Switzerland in particular was a PITA for porsche in this respect.

Originally posted by jazzbass
Here's what I've heard from various people/websites, all of which is subject to correction by those who actually know what they're talking about. Air cooling was a *60's* thing. By the early 70s, Porsche knew water cooling was the way to go. Furman thought the 911 was dead, and the 924 and 928 projects were the replacements. But the 911 kept on selling, despite little to no development effort on it until the late 80s (why didn't we get a good shifting transmission until '87?). So Porsche wanted to all water 30 years ago. Fortunately for us, people kept buying those darn air cooled 911s.

Yes, the 928 was supposed to be the replacement. When this scenario didn't play out, money for 911 development was very tight for many years, really up until the 964 was developed.

Originally posted by jazzbass
As for racing, I've heard they wanted to go water cooled as early as the 917, but they couldn't becuase of a contractual agreement with VW. Apparently Porsche was getting sponsor money from VW, and VW wanted an air-cooled race car, since they're whole product line at the time was air cooled (Bug, Bus, Type 4s). I read this on some random website devoted to LeMans and have no idea if this is true or not.

This sounds very suspicious to me. no offense.

Originally posted by jazzbass
For now, however, I think the "water-cooled" stigma you see on this board comes a lot from the (IMO) bland styling of the 996. If they would have stuck the 996 engine in a 993, things would probably be different. Oh - they'd need to keep the dry sump, too. No 911 should have a wet sump engine.

Hear, Hear!! I would love to see how things would be different if this was the case. Witness the respect the GT3 gets from some techies hear compared with a normal 996... Not least because it has the dry sump, even though it still has the 996 styling. the 996 seems like a big car to me, just like a 944 does. Credit goes to porsche, though, for not increasing the weight meaningfully between 993 and 996.

[Bill Verburg]

The modern water cooled GT3 and GT3RS are some of the best engines Porsche has ever produced. That said, they belong in a chassis designed for them.

[JMar]

"Originally posted by jazzbass
As for racing, I've heard they wanted to go water cooled as early as the 917, but they couldn't becuase of a contractual agreement with VW. Apparently Porsche was getting sponsor money from VW, and VW wanted an air-cooled race car, since they're whole product line at the time was air cooled (Bug, Bus, Type 4s). I read this on some random website devoted to LeMans and have no idea if this is true or not.

--------------------------------------------------------------------------------

Kobalt


Actually jazzbass is correct here, please read the revised excellence was expected where this is explained by one of the Porsche people involved with of the program. I believe this is in the section devoted to the 917, but don't recall the pages. Basically Porsche's racing was subsidised by VW as long as they used air cooled motors. I'll look it up tonight and provide page numbers is you still have a hard time believing this.

[KobaltBlau]

Originally posted by JMar
Kobalt


Actually jazzbass is correct here, please read the revised excellence was expected where this is explained by one of the Porsche people involved with of the program. I believe this is in the section devoted to the 917, but don't recall the pages. Basically Porsche's racing was subsidised by VW as long as they used air cooled motors. I'll look it up tonight and provide page numbers is you still have a hard time believing this.

Huh. Just sounds strange, I hadn't heard of any of that.

[BlueSkyJaunte]

I have to wonder about the 2-valve / 4-valve reasoning...why? Well, I just drove an '04 Viper, which makes 500 hp, and has 2 valves per cylinder.

Couldn't Porsche have just stuck with 2-valve heads?

?? ??

[Hugh R]

I heard that one reason VW got rid of air cooled cars was they couldn't meet the oxides of nitrogen (NOx) emissions standards because of the high combustion temperature which formed the NOx

[JMar]

Originally posted by KobaltBlau
Huh. Just sounds strange, I hadn't heard of any of that.

Yeah it was a big hush hush at the time, and was "publicly denied" now however the truth is known. In case anyone would like the details see the latest edition of Karl Ludvigsen's Porsche Excellence was Expected Volume 2 page 564. For those who don't have the book (first of all what is wrong with you, get it!) basically it states that The agreement between Carl Hahn (of VW) and F Piech was that VW would accept 2/3 of Porsche's racing budget as long as all Porsche's competition cars used air cooled engines.