In the late 70's VW decided to go water-cooled, I gather to keep up with emission requirements. Porsche, obviously wanted to early on as well, with their 928 (intended 911 replacement). But, it seems they were able to keep their engine air-cooled way up into the 90's. Yet, they too went for water as well, even though they seemed to have conquered all obstacles. I alway wonder: did they need to? Why couldn't the engine continue to be developed as air-cooled? Materials are getting better all the time, and they actually want engines to run hot for greater efficiency, so why did they wimp out? Opinions?

I understand engine noise levels had something to do with the change. Reaching required emission standards probably had a part in the change, as well, and KEEPING the levels low over the life of the engine, and in all running conditions and modes was certainly a consideration. The Cap'n

Late 70's ?? VW had the water cooled Rabbit / Scirocco out in 1974.

One of the reasons Porsche went to the current watercooled configuration was to utilize 4 valve technology.....of course I can't remember where I read that, might have been Bruce Anderson's 911 performance handbook?

But everyone loved that sound.

The impetus for the 928 was concern over impending emissions and to a greater degree (appartently, as relayed by Ludvigsen in "Excellence was Expected"), noise. Europe lagged the US in requirements for pollution controls, but not noise controls. By the mid-eighteis, the HP barrier could only be broken with watercooling of the heads (962), and the 3.2 in the 89 carrera was prolly the most efficient air-cooler made. But the HP/KG curve compelled even better. To me, the value of air-cooling is weight savings. At some point, the same argument supports water cooling as well.

Water cooling was the only way to raise the hp per liter. Also, the 911 flat six is pretty maxed out at 3.8L.

Besides emmissions, I think it was also a cost saving measure. The old 911 engine was pretty expensive to construct compared to the new ones.

In fact, that's one reason I wanted a /6 instead of a /4...

Skip

There is a differance between "sound" and "noise".....

The Cap'n is correct, even the type/size of tires that Porsche and other manufactures have wanted to use has lead to certain models not being legal in some countries.

As much as I like my air-cooled cars, water is better for precise engine control of emissions, you can run higher-compression, the tolerances of the motor can be tighter....any mechanical device is going to work best at a particular temperature, with air-cooling, it is much more difficult to obtain that "ideal" temp with the outside temperature changing all the time and with the loads on the engine changing all the time.

Even Jakes DTM is not perfect...if operated in a very cold climate, the motor might never achieve the correct warm up temps unless changes are made..

that's funny, I've gotten more compliments on my /4 (with header) than the 3.6 air-cooled motor in my 911

Manufacturing.

I have had several of the new gen engines apart. They are stupid simple. Imagine HALF the pieces that are needed to assemble a 3.6 air cooled engine. NO joke.. they mimicked the Japanese and Chinese when it comes to manufacturing techniques.



B

This is a perfect place to unveil the prototype for my new registered trademark...

It pretty much says it all... The full color version is almost completed.. It'll make awesone T shirt...

Click to view attachmentClick to view attachmentThis is a perfect place to unveil the prototype for my new registered trademark...

It pretty much says it all... The full color version is almost completed.. It'll make awesone T shirt...

Ha ha.. you where a Marine huh ??LOL

Lose the eyes with tears and you have a winner!


B

Now I see the skull!

It looks like he's got a tear drop of water coming out of his eye.... lamenting the extinction of air cooled engines? Reminds me of that Indian in those pollution commercials.

Yeah, but I'm an old fart. Early 911s were the dream cars of my youth.

that's not water.....it's OIL

I don't know if it's true or not, but I read somewhere that getting 4 valves per cylinder was a consideration as well.

Like the man said, "I'd buy that for a dollar!" Lookin' good...

Did Porsche have to go watercooled, yes.

The amazing thing is they managed to stay aircooled as long as they did. Only a private German company would do that. I morn the passing of the aircooled Porsche engine, but Porsche developed it well past it making any sense.

Assembly, noise, emissions, economy, efficiency, all are better with a modern watercooled engine and have been mentioned above.

Don't forget what happens when aircooled engines run lean. I would think all manufactures selling in the US are using lean burn technology for efficinecy and emissions.

Jake that logo needs to be put on a bowling (or mechanic's) shirt. That'd be worth at least a couple of dollars.

Very accurate reply on all counts - same thing a former Porsche engineer told me.

Water is better.

Among other things, air-cooled motors tend to cool less evenly than water-cooled ones. (Ask Jake how much work he's had to put into getting just the right amount of air into just the right places...) It's easier to do with water, at least if you're doing a total blank-slate redesign.

I recall an interview in Pano a while back, where one of the company engineers was quoted as saying, "The only thing increasing the displacement will do is give us more torque. We need four-valve heads if we are going to make more power."

Lots of reasons to go water-cooled. Emissions, noise, four-valve setups, efficiency, ease of manufacturing, cost... And so on.

Air-cooling has its own appeal, though. For me, at least, it's mostly the sounds. And, at least in the T4, the simplicity.

--DD

What is it about four-valve setup that requires water cooling?

Are there pictures around of the engine in whatever it is they call a 911 these days? Is it basically the earlier 911 boxer with water-cooled heads (a la Vanagons) or is it a completely different engine?

Skip

Hmm, I would check your sources on that one. You want more heat rejection for greater efficiency. There is a block temperature that yields maximum efficiency in steady state that can be acheived in both watercooled and aircooled engines.


Brad, you're right on about the street motors, but the race motors are not japanese crap. They are watercooled 964 motors and are amazing. I would love to see those in street cars... oh wait, go buy a turbo, gt2, or gt3! They're big bucks. Porsche couldnt keep making $80k cars with 964 based motors. So either they make high performance $120k cars (gt3, turbo) or they make compromised $80k cars... or both. Remember, the 996 technologically light years ahead of the 993. The production costs are WAY higher on the rest of the car, so to maintain the same price they had to cut somewhere.

There is no reason that a 4-valve setup can't be aircooled, besides convenience. With a swirl pattern, the intake valve is right next to the exaust valve on either side. Makes it hard to keep things in tolerance. Going water cooled lets them avoid going at really invasive angles to spread the valve stems apart. Really exotic valve patterns aren't as hard to achieve with a push-rod engine. Some of the drag guys do some weird stuff. But with a pushrod, you can mount the lever at in almost any position. With overhead cams, the valves have to be inline with the camshaft.

Also... Swirl pattern.
Intake Exhaust
Exhaust Intake

Done so that the air swirls in the head really aggressively. Big power.

I do believe that the later 917s had 4 valves per cylinder. Or all of them did. Its hard to remember. One of Porsche racing models had 5. 962? My brain hurts.

Any questions?

There isn't anything specific to the four-valve heads that keep them from being air-cooled--there are lots of motorcycles out there that do it! But Porsche found that they could not do it effectively in the 911 engine. Something about not having enough room for enough cooling fins around the exhaust valves (???).

They tried it, they couldn't make it work. Definitely not for street engines.

Alpha, the 962 had water-cooled heads. Five-valvers were no problem on it (though I think they were just four-valve heads). And where did you get the idea that the 917 had four-valve heads?
http://www.ultimatecarpage.com/frame.php?f...&carnum=418

Matt is quite correct about the different "families" of engine; the race cars and Turbos and GT3s and so on have what is basically the 1990-94 Carrera 2/Carrera 4 (AKA 964) motor, with water-cooled heads (and cylinders?). The regular 997s & 998s have the newer simpler engines.

--DD

Well....

That site is giving the specs for the /K. There were a lot of revisions. I mean 600 hp? come on! The /30 was making what? 1200?

917...
Early- 12 cylinders NA
Early (2)... 12 cylinders NA, with fan drive relocated
Mid... 16 cylinders NA
Late... 12 cylinders Turbo

I just remember reading somewhere that one of the versions had 4 valve heads. They changed nearly every year. Bleeding edge technology...

Does anyone really question which is more efficient at cooling? Air vs. water? Clearly water. Anyone who debates that isn't facing reality.

Just when I was good at keeping my flame bait comments outta here, I go and say something like that. Oh well. Obviously there are a lot of design variables.

Having said that, let this be clear: If I could put ANY motor I wanted in my 914 today.... I would choose a 2316 built by Jake. Over 200/200 in a reliable 100k motor based on the original power plant. Yeah. THAT rocks.

Actually swirl is is bad for maximum power. You will find many race engines are designed to eliminate swirl and tumble. Swirl is however great for part throttle emissions and fuel economy.

On an Otto cycle engine the more heat we can keep in the chamber the better. Heat rejection is bad. Thermodynamic efficiency is one reason why diesel engines are more efficient than gas engines. Also the amount of potential energy in the fuel is another reason. (but this is kinda off topic) In reality if we can keep the materials stable the hotter you can make the engine run the more efficient it will be.

It takes something like 20+ hours to assemble an aircooled engine on the production line. It take 12 (I think) to assemble the water cooled engines. The lower end engines are not as good as they could be. Many of them can't handle running on the track with DOT-R tires.

Another reason POrsche had to go watercooled is sound emmisions. Aircooled engines are very noisey, just from the external noises. Cooling fan, valve noise, cooling fin vibration, etc. Water muffles much of that noise, thus making it easier to pass strict European noise regulations.

Watercooled engines are much more stable and it is easier to control emissions levels, throughout the different engine cycles.

The 917 used standard Hemispherical head design. Although Porsche did design a complete set of Beryllium pistons for the 917 engine. Never made it into the engine. Price...., if you have to ask.

Knew you guys would nail it eventually, and this is the most concise, correct answer here. Pretty much covers all the bases without going astray and wrong.



There are some other good/interesting ideas floating around here, too, but a lot of comments here are either being made casually from (faulty) memory or a lack of real knowledge, esp. with regards to 917 engine technology/progression, 996 vs. 993 chassis production costs, and the limitations of four-valve setups in air-cooled 911 engines for production purposes.

Don't mean to bust anyone's balls -- or get into a pissing match -- but I just hate seeing misleading info on a board that usually has so much good info...

It's up to us to keep the history correct for future Porsche/914 nuts. How many newbies will come along and read this, take it as gospel, and spread it on from here?



pete

Whoa, you're absolutely right. I'm glad someone caught me.



thermal efficiency (eta, th) = q,out/q,in = 1- (T5-T6)/(T4-T3)

I was mistakingly calling the 4 to 5 expansion the heat rejection, but its really the power stroke.

i got

Ouch. Be careful whose information you discredit. Porsche has many young employees.

Yep, they are specially designed water jackets with press in steel cylinder liners. They are actually a little different from the 964 case, but not terribly different. I know the case bolts are different in a race engine, for instance. The 996 GT3 cup engines actually have a 964 part number, but the 997 GT3 cup and most of the other 3R shit is 996 part number.

The 993 aircooled engines experimented with smaller width on the main bearings, which was good for the aircooled, but isnt strong enough for the big power in the watercooled, so they run the beefier 964 main bearing journals in the race cars.

The 996 and 997 generation street motor (dunno about the 998 ) has two identical heads that are flipped from left to right, so theres one less part number. There is a timing chain at the front and back of the engine. This is very different from any other flat 6 porsche has made, but its much less expensive to produce. The entire crankshaft is also on a carridge that torques together and bolts up for quality control in bearing tolerances and ease of production.

Matt,

are there any exploded views of these 964 based watercooled motors?

thanks,

Mike

http://forums.pelicanparts.com/showthread....mp;pagenumber=1

Some wonderful pictures of a 962 being rebuilt I think by Neil Harvey (Performance Developments/LINK USA)

Of course water caries heat away faster, it has 4 times the specific heat. The engineers knew that back in the 30's and 40's, so the air cooled engine didn't become into existence because of a misunderstanding. Simplicity of design, weight, reliability, the all came into the design.


I was just thinking about this, didn't the 959 have air cooled cylinders and water cooled heads?

Hey Matt! Sorry, I am not trying to discredit you and read your note with interest and respect given where you work, but I would love to hear more information on how the 996 chassis costs more to produce than the 993 did.

While some of the tooling was paid for long ago on the 993 chassis, nearly 50 percent of the 996 platform (everything from the seats forward, in fact) is shared with the 986. If the 996 per unit actually costs more, then surely Porsche is spending less on platformS when you look back to the 968/928/993 period.

But I'm just not sure the 996 body, when completed, costs more to produce. Look at all of the ways that things go together. The 993 was the first step towards more efficient production after the expensive and labor intensive 911 and 964 platforms, but the 996 took "efficiency" to new heights. Just look at the snap-together center consoles. These things were meant to go together once very quickly on the line and then be taken apart/put back together only so many times...

Again, if you have information that states the 996, less engine, was more expensive to build than the 993 less engine, I am all ears -- and VERY interested!

No offense meant...

pete

Yeah, the 959 was like that 962 if I understand correctly, but with aircooled cylinders. Now there's engineering :-) I'd still like to electron beam weld a Nickie onto a cylinder head....

Do you have PET? Go look at the 996 turbo. If not, I dont have anything on my computer other then a snap shot from PET I can take for you.

I dont have any numbers, but I do have 2 friends I worked with that informed me. One worked in Weissach on traction control for the street cars and we were talking about how much more money goes in the R&D side of the new cars then the older ones (even the 993). Stuff like advanced ABS, knock control, TC, PASM, etc. add to the costs of the 996 over a 993. This is coming from a guy who designed the stuff... Weissach has grown in size tremendously since '99. They just built all new facilities and have nearly 3000 employees in R&D now... which is the only reason I applied to go work over there.

Another friend I worked with is now in Stuttgart writing his masters thesis on process engineering. He confirmed everything I said. Of course the Germans see nothing wrong with the new honda based watercooled motor because its german engineered, but it costs much much less. The entire car as a package has a similar cost to the 993 though just because its more technologically advanced.

You make a good point on the snap together interiors. The 993 interiors I worked with all seemed really basic and not really interiors, more like pieces of cardboard with leather stapled to it (like our cars). The new interiors are very complex and expensive to manufacturor. They are easy to assemble because you have to assemble half the goddamn interior to do a service.

I hope I'm teaching you something about these cars and not coming off like I'm trying to fight you. I've spent some time trying to understand how the krauts work. More money in R&D and WAY more money in making things cheaper to assemble. So the final product is less expensive to produce, but they invest a lot to make it that way.

That is a current trend in the automotive industry. Cut production cost and increase efficiency. Ford just went through a major restructuring of their logistics and supply chains to increase efficiency and cut cost. Look at Toyota and Honda. They place a premium on efficiency and their prices and quality reflect that. Compare the quality of American and even German cars to the Japanese. They aren't even on the same level. Everyone is trying to copy the Japanese. Even the Germans for the most part have as many problems as the American manufactures. Their cost are pretty high and it is reflected in their cars.

I know some Porsche gearboxes are made by Aisin instead of Getrag. Not Sure why though.

Anyone remember AdvanTec four valve heads for the aircooled 911? Wonder how well they worked.