What technical innovation led to Porsche going to water cooled engines on 996?

I saw a special last weekend on Porsche and it said something about technical improvements led Porsche to using water cooled engine design for the 996 and boxster. I don't remember why. Does anyone know what improvement in technology led Porsche to switch from air cooled engines to water cooled engines? Thanks, Mark

I did some reading on this when I went from a 993 to a 996. It was mainly to meet tougher emission standards by applying engineering to have a better combustion. I think that required 4-valve heads and that couldn't been done without water cooling. Apparently, air cooling wasn't enough anymore. As to the crankcase, it was just cheaper to make a whole new water cooled engine.

Porsche couldn't safely get more HP out of the engine without going to water cooling. There's a very good reason why there aren't any high-powered air-cooled cars in the world! You simply need the cooling power of water.

Noise. European noise abatement laws could not be met with an air-cooled car...

well there are 2 sides to this. 1st is the production of the engine it's self - a "crate" 996 motor is about 12K (no core) or 8K with core - this implies that the total cost of the motor is cheaper than a 964/993 motor at 25-30K for the motor (no core). when the 996/986 series were being developed they hired toyota to help stream line the production of the cars (same front clip, block dimensions, etc). to standardize the production tooling. Volume = cost reduction. The use of water cooling was nessecatated for packaging reasons in the boxster The second reason is the european emissions compliance and the need to move to a simple 4 valve system to meet them. the air cooled engine by it's nature is extreemly dificult to get to meet the new and upcoming restrictions. by water cooling the motor you have a means of making the engine more effecient with the same or better power. The Air cooled cars can easily make the same power ranges and the water cooled motors however they do it with a need for tighter tolerances - more radical engine mapping, etc. none of these are good for emissions compliance, etc. Tighter tolerances again drive up costs (cas in point is the GT-3 motor at 50K for replacement, incidently this is based on the 964 block with water passages added) ultimate engine noise is determined by the exhaust system primarly (# of cats (the 996/986 now have 4 btw) muffling systems etc. and less so by the water/air cooled nature of the car. packaging is a consideration as well since there is not much rool on a 996 for mufflers. My 2 cents.....

Rob: Thanks. Nice analysis. I knew the answer for going to water cooled engines was to meet more stringent emission standards, but I never saw an explanation before of why that was the case.

Two points were critical in the move: Noise, the water jacket does significantly reduce noise....it's not just the exhaust, and Heat dispersion: it is hard to get the heat away from a multivalve head and the water cooling is basically essential for this. (water cooled heads were used in some earlier "air-cooled" Porsche competition cars). This is, of course, associated with the tolerances and build complexity and achiving relaible high combustion temperatures is part of the emissions equation. The benifits of streamed production and common parts are clear economic improvements in the running of Porsche but they are not the basis for the mechanical configuration. In the end the decision was based on having a engine line that would be longlasting, cost efficient and useful in different applications.

There are many factors involved: More HP = more heat and our air cooled motors are really oil and air cooled as the oil system is used for cooling as much as for lubrication. Compare the last air cooled NA engine (993C2S) at 282 HP versus the 996 GT3 which uses the same dry sump block in a water cooled configuration at 380 HP. Do we want to carry around 20 liters of Mobil One? Space = air cooled engines need to cool the heads this means cooling fins. Adding extra valves to improve combustion means less space for cooling. The Porsche 962 race engine had water cooled heads for this reason. More Valves = improved combustion for better power, emissions and fuel economy. The air cooled head can't handle more valve area for the reasons above. Noise - The Swiss have very stringent noise restrictions and it's an important market for Porsche. The air cooled cars have a hard time meeting the noise standards - witness the 993 which has a cover under the engine, one which we should all remove as it traps heat (as well as noise) and has been shown to lead to premature valve guide wear. Liquid cooling reduces engine noise (and I don't mean exhaust) the water jackets quiet clatter and dispense with the noisy cooling fan needed for the 993 and earlier engines. Power (I know I said this but we're talking P_O_W_E_R) = the water cooled engine in the GT3 is a very high power per liter, unequalled by any emissions controlled road going Porsche. The use of 4 valves and variable cam timing makes thius possible in an engine which is tractable (unles some very peaky race engines). Best,