Did Porsche have to go water-cooled? Options

[pbanders]

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.

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

[Brett W]

Water is better.

[Dave_Darling]

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

[smontanaro]

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

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

[MattR]

and they actually want engines to run hot for greater efficiency

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.

[alpha434]

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?

[Dave_Darling]

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

[alpha434]

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...

[Rand]

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.

[Brett W]

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.

[horizontally-opposed]

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

--DD

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.

(IMG:style_emoticons/default/clap56.gif)

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?

(IMG:style_emoticons/default/hide.gif)

pete (IMG:style_emoticons/default/ph34r.gif)

[MattR]

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.

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

(IMG:http://www.grc.nasa.gov/WWW/K-12/airplane/Images/otto.gif)

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 (IMG:style_emoticons/default/owned.gif) (IMG:style_emoticons/default/biggrin.gif)

[MattR]

but a lot of comments here are either being made casually from (faulty) memory or a lack of real knowledge ... 996 vs. 993 chassis production costs...

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

[MattR]

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

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 (IMG:style_emoticons/default/wink.gif)) 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.

[Mueller]

Matt,

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

thanks,

Mike

[cnavarro]

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)

[thomasotten]

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

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?

[horizontally-opposed]

but a lot of comments here are either being made casually from (faulty) memory or a lack of real knowledge ... 996 vs. 993 chassis production costs...

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

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... (IMG:style_emoticons/default/beerchug.gif)

pete

[cnavarro]

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....

[MattR]

Matt,

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

thanks,

Mike

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.