Those are not for water cooling.

I believe you a fighting a losing battle here.

I have never, ever, seen a water cooled head conversion on a modded car. I guess that doesn't mean that no one has done it. I have seen a couple cars with coplete engine swaps from 996 GT3 / 996 TT etc. etc.

A more pertinent question is: name any engine (water cooled or air cooled) that produces 100 bhp per liter that will stand up to extended floggings and track use on an extended maintenance schedule. If you want an eye opener, do some research into the rebuild times on modern water cooled Porsches. In the past several years the SCCA (pro) world challenge cars had 50 hour top ends! Machines that are run hard do not last 100k miles.

More on the topic of this thread:
As Steve W pointed out above. Water cooled conversion parts will not be cost effective. It would be a far better use of your money to turn the output up, and maintain the engine as necessary.

Plus water and radiators are heavy to carry around! Added aftermarket complexity will also most likely detract from the overall experience.

 

I don't know that there is a battle.

The original question was what was the rational behind water cooling.

I didn't know it was going to turn into what was better, which I never got into.

Personally I like the simplicity of air/oil cooled myself.

 

Let's get back to basic engine design 101:

1. Power is proportional to rpm & cylinder pressure, therefore to make more power from an aircooled 911 engine you either have to increase cylinder pressure at existing rpm or increase the rpm whilst maintaining existing cylinder pressure. For example, take a 3.8 993RS engine making 300hp @ 6500rpm, increase peak power rpm to 7850rpm whilst maintaining the same cylinder pressure and you get 350hp.

2. Next consider what is happening in the cylinders. A 993 turbo engine makes 408hp @ 6000rpm, in comparison to above 993RS engine to do this requires 31% more cylinder pressure (408/300hp x 6000/6500rpm x 3.75/3.6litres).

3. Cylinder pressure is directly proportional to the temperature change in the cylinder (Boyles Law, PV/T = constant), so if the cylinder volume is roughly the same (3.6 to 3.75 litres) the temperature has to increase by 31% to generate the additional pressure.

Hence it's pretty much a given that a stock 993 turbo engine runs roughly 30% hotter at peak power than a n/a 993RS engine. This is easily verified in testing on the road or dyno.

Hence can someone please point out the error in my judgement that explains why a 400hp, 8000rpm 993 n/a engine running with 25% less cylinder pressure than a stock 993TT requires watercooling to be reliable??

 

I have no idea what you just said or what it means...I do know you, are an asset to the Rennlist community.

 

Obviously, Porsche didn't agree.

 

I understand 9's arguement.

However, there has to be some other dynamics in play.

to get 400 hp is going to require X amount of energy reguardless if it's at 6500 or 8000 rpm. And energy is heat so it would also reason that at peak power the temps should be similar.

maybe I am missing the cycles calculation.

Now what I am sure he is speaking of is combustion temps, because external or oil temps don't make sense. IE that equates to 72 or so more degrees of temp which would put the oil temp past 300 degrees. We know what happens to oil at 300.

However, again I am not trying to make an arugement one way or another for why the factory thought they needed to water cool their motors, but they did.

Just offering the factory response. They were looking at homologating the 911 down the road and felt that water cooling was the answer to being reliable and competitive at the same time.

 

BMW S50B32 (ROW e36 M3 engine) and S54 (e46 M3 engine) are probably the closest OEM motors to your definition. Theyrw fairly bulletproof and don't require much more maintenance than they're more pedestrian passenger car variants ~ and respond well to heavy track use (at least in the 'amateur' racer sense).

As far as this being a battle - its not. Just a conversation on the limits of an air cooled motor. Porsche obviously thought the mid 400 range, at least from an OEM standpoint, with all its inherent limitations. From the aftermarket/enthusiants standpoint, the limit I think is much much higher, as has been proven time and time again by guys like andial, RUF, protomotive, 9m, and many others.

BTW, if porsche thought the upper limit to be 300, how do you explain every turbo from '91 on?

 

That BMW striaght six is just about indistructable.

I think Porsche knew by then water cooled was in there future.

The were using all kinds of super exotic stuff on the turbo engines.

300 is just an even kind of generic number that was tossed out, and I am sure there is some exact spec somewhere in Porsche vaults that specify what that number is, but it's somewhere in the low the mid 300s. At least that was all the talk was about when we first heard they were doing a water cooled 911.

I am not saying it's not possible. I have friend who has a well over 600hp (630-640@ the wheels!) A/C 930, so I know it can be done.

Let me ask you: why did Porsche go water cooled? What do you think the reasoning was?

I am also interested in NineMeister's cylinder pressure calculation.

How exactly did you derive at those numbers any way?

Obviously you can't calculate a hard mechanical number on something with boost.

I am just curious.

I am not afraid to learn anything.

 

The answer to the original question is, yes there would be a benefit as long as the system was designed properly (the engine would be able to withstand more combustion energy) however this is assuming all of the hardware and software are capable of producing this additional energy. Then the next thing you must realize is, the cost/benefit ratio is not favorable for 99% of air cooled 911 owners.

400+ hp air cooled has been done many times over and costs a small fortune

 

I must say, the BMW motors of the mid 90's, vs. Porsche's - there's a wide gap in engineering, it seems. In 1995 BMW had the 3.2l S50B32 making 100hp/liter (321hp DIN) in road-going street cars (M3's), revving to 8000. Porsche had the 993 3.6 non-VR making what, 272? I'm not convinced water cooling was the big reason for the difference though, still - the BMW had ITB's, 4 valves/cylinder, dual VANOS (infinitely variable cam timing on both intake and exhaust), etc.

I still like my Porsche much better overall than my Bimmers...but still, the engineering was incredible. 15+ years later there aren't many N/A engines that approach the same specific output. Anyways, I digress:

For heat management? Like what?

Not trying to be argumentative at all, just honestly don't know. What is there "exotic" to be done to cool it down (and affordable enough to include in an OE application)

If you aren't saying that its not possible, then what are you saying? This one has me confused. I know you say 300hp is just a generic number - but is it accurate? Correct me if I'm wrong, the original topic was whether 300hp was the limit or not for an air cooled motor...you yourself have a friend proving it's not...and I doubt there's anything that exotic keeping it cool, no?

Lets just say, that I think the factory looks at the limit as the mid 400's. The ROW 993 Turbo S made 450hp...and that was a warrantied, general consumption, road-going car, expected to run to 100k+ without trouble (and the most powerful regular-production air cooled car, no?). I doubt they would have released a car to the general public that they themselves didn't expect to last.

I don't KNOW all of the specific reasons Porsche went to water cooling, I don't think anyone but Ferdinand Porsche the senior himself knows (). But I do have a general idea - power and emissions. But, it wasn't the 300hp mark they were trying to surpass - they were far past that already. Water cooling allows them to sell a brand new 612hp 997 GT2 RS that will be as reliable (under 'reasonable' use) as a Boxster.

Emissions - both sound and exhaust - were getting increasingly more stringent. The air cooled motors, as you know, are LOUD, even with a stock exhaust - just the mechanical clatter of the whole thing spinning around is enough for the "unwashed" to think something is wrong with my 964. The water cooled motors are much quieter driving by - and that satisfies the politicians, I guess. As far as tailpipe emissions - water cooling is more efficient at keeping a combustion chamber's temps steady - which means Porsche can run hotter temps, creating more power (yay! for me, the future owner of a 997.1 GT3) and lowering emissions (as you know, the hotter the chamber, the more complete the burn - therefore lower emissions - yay! for the trees and little furry animals and stuff). I know in some areas of the US, air cooled cars used to be given emissions exemptions back in the 70s (my dad worked for PCNA and has related stories to me about this) - because even back then, Porsche & VW were having trouble keeping up with legislation. Those kinds of exemptions were long gone by the late 90's, and Porsche had to do something.

Yeah dude, I dropped out of Greek pretty quickly back when I was in school...I'll let the experts translate

Let me be clear - this is all based off of my *fairly* solid automotive knowledge base, and uncommon sense. I know nothing specifically about Porsche's switch to water cooling, but I do have my hunches, and my hunches are known to have (at best) about a 50/50 chance of being right

 

Q: What's the best way to make a small fortune in the P-car business?

A: Start with a large one!

 

Things like sodium filled valves that were $300 ea found in stock turbos. and other bazzar metals. Yes, specifically for heat dissipation. A NA Carrera valve was about half that much.

To be honest I am not really sure what he had in it other than $100,000 maybe, maybe more.... and it was just a killer DE car. In it's final configuration it probably didn't see more than a few thousand miles.

I will buy into the noise issue becasue they, Europe was coming down hard on that with Porsche in particular.

It is hard to say about emissions because the figure that out very strangely depending on who is doing the figuring. And guess I could research it more when it started and who started but in some emissions figures they take the entire sum of emissions: Exhuast, and any regular maint. fluids that are taken out of the car specified from the factory and are given some value for it.

It's one of the reasons you see 10k oil change intervals on Audis.

I understand 400+ aircooled engines have been done thousands of times. I just wonder if any have gone 100s of thousands of miles like their stock counter parts.

Just even on the stock turbo cars going back forever they were never as reliable, lasted as long, or were anywhere near the cost of a NA car.

 

Porsche must shop at Turkish Bazaars


Turn 'em on to an Afghan Bazaar, and list on that new turbo might be a few grand cheaper next year (sorry, I had too!)


Thinking back, I guess I knew that about the sodium valves. Thanks for reminding me, pretty trick technology

Don't the (non-GTx/turbo) water cooled cars have a significantly lower oil capacity? I'd think getting rid of the Exxon-Valdez-esque oil change would more than offset the odd coolant exchange. Plus isn't that more of a importation/certification emissions thing, rather than a local/annual emissions worry?

Certainly no, they haven't. That's largely a function of their use though - how many build a 350hp N/A flat six to drum along the highway?...how well does a stock 964 lump hold up to the conditions that the high dollar race engines are built for, though? Some will run as long as the owner wants...a few will pop on their first DE (I've seen it (rod bolt let go) - certainly not a slight against the M64, nor is it normal/anywhere near common, just an observation/sample of one).

What would be a more interesting comparison - a well built 3xx hp 9M (as an example) vs. a water cooled 996 (w/ similar output levels) motor on the track. I'd be really interested to run a fleet of them verses each other for an extended period, tracking maintenance and repairs. I know where I'd put my money...

This has been an interesting discussion, and I know I've learned a lot. I'm going to bed though...maybe!

 

I think some of it is from UFO technology.

Yes, when they went to water cooled they also went to a wet sump, which was a big mistake. Although Porsche has corrected that now.

 

Cylinder heads being water cooled vs air cooled is no mystery. The cylinder head is subject to a great majority of combustion heat. Outside of Porschedom for instance you can view 100s of 1000s of cheaper engines with scored cylinders from overheating conditions. The greatest heat and pressure is in the first 1/4 inch of the top of the cylinder and in the head. Air cooling for all manufacturers became a dead end due to emissions regulations. Air cooled cylinder heads need a richer fuel mixture for cooling than water cooled. The same can be said across the board for detonation with higher boost, higher compression, and so on. Beyond that, 4 valve heads with more complex dense centers are difficult to cool with air. Especially between the exhaust valves.
Ok great, now that the two pages of pointless arguments of a decade ago are settled, has anyone ever compared the stud spacing of the 997 heads to a 964, 993 or anything? You would have to weld up the coolant holes on the cylinder head surface and then mill them. Add something like a fuel rail on each head to feed the coolant in. Also machine an inner and outer timing cover to work with the heads. Oill feeds and modified air cooling shroud that stops at the top of the cylinders. Intake manifold? Whatever works, GT3 would work.
This could run leaner, higher peak combustion pressure, extremely improved head flow and combustion chamber design. All meaning a far better volumetric efficiency up near 100%.