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Sorry, but this is wrong. An air-cooled (technically oil cooled) car has no problem with the transfer of heat. Porsche themselves ran the 917/10k with a flat-1
by brc 11y ago
Sorry, but this is wrong. An air-cooled (technically oil cooled) car has no problem with the transfer of heat. Porsche themselves ran the 917/10k with a flat-12 air cooled twin turbo engine that could make 1000hp reliably.
The transition to water cooling in the 911 was done for noise and emissions purposes primarily. A side benefit for them was the ability to buy off-the-shelf HVAC componentry and not have to engineer a heating system based on exhaust heat exchange.
It's very easy to get equivalent horsepower out of an air-cooled engine than the current water cooled models. There are plenty of air-cooled turbos pushing 600hp, and the Singer Vehicle Design 911 engines are producing 400 hp based on the original air-cooled 911 engine.
- grecy 11y agoI understand how a water jacket helps with noise, but how does water cooling help with emissions? I would have thought an air-cooled engine would run hotter, therefore burning more of the "bad" emissions before they even enter the exhaust
- semi-extrinsic 11y agoLower combustion temperatures give a substantial decrease in NOX emissions. Burning off bad stuff is the catalyst's job.
- brc 11y agoIt's also the gigantic whirring fan on air cooled engines that is removed with water cooled engines which lowers the noise down significantly. One of the initial engine designs for the 911 was a twin-fan engine. Apparently it made such a racket that the porsche engineers nicknamed it 'the threshing machine' and Butzi Porsche canned it on the spot.
- grecy 11y agoI don't think I've ever seen a water cooled engine that doesn't have a radiator fan (or two). Older ones are crank driven, these days they're electric.
- brc 11y agoSure, and the crank driven fans have been replaced by much quieter variable speed electric fans as you noted. These are also more efficient as they can be switched off during highway driving. There are also the thermo-couple engine fans where the amount of fan-clutch engagement is driven by engine heat. My other car has one of these and sounds horrendous when driving in heavy traffic on hot days, but is mostly silent all the other times. But the big difference between a Porsche air-cooling fan and a crank-driven engine fan is that a Porsche fan is overdriven and much larger (diameter and blades) than a typical water cooling fan which is typically under driven and has fewer blades.