Dirty exhaust tips and Porsche engine break-in methods

Clean-burning M96 exhaust tips
Clean-burning M96 exhaust tips

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:


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