There are times when Porsche AG shares plenty of information, and other times where one’s curiosity runs ahead of its press releases. One item that’s always made us wonder: Why do new DFI engines from 2009-onwards have heavy carbon deposits on their exhaust tips? (This is true for other makes, as well.) Shouldn’t the new engine be cleaner? M96 engine port-injected exhaust tips are usually light gray to clean. As it turns out, emissions are the short answer to that question.
Last fall we had an opportunity to ask a Porsche AG tour guide, Gerard, just why those DFI tips are often sooty black? His answer: To heat the catalytic converters rapidly during the cold start cycle, the DFI system deliberately runs a rich mixture to ignite fuel with the exhaust valve not fully closed. That heats the cats quickly to their optimum temperature and better meets emissions standards — the side effect is the carbon residue on the tips.
Also in the curiosity department, Ken Koop of the Porsche Club of America’s Yellowstone region had the opportunity to ask a Porsche engineer in Zuffenhausen why the owner’s manual specified such a long (2000 mile) low-rpm break-in period, when the factory itself, on a dyno, runs much higher rpm on just-assembled engines? The answer is most illuminating and well worth the read on PCA’s website: