Jaws1

i previously owned a 997.2 and was constantly having to clay bar the rear bumper in order to get rid of the exhaust soot. The car did burn a little bit of oil, but I think the soot was mostly a function of the DI. I picked up a .2 C2 yesterday and the tailpipes are remarkably soot-free. Is there a difference between the 9A1 and 9A2 to account for this difference?

subshooter

I have two Porsches, one with the 9A1 (38k miles) and the other with the 9A2 (5.2k miles). I have never experienced any soot on the bumper on either of them. I have a lot of soot that builds up on the 9A1 exhaust tips though. On my 991.2, it has black tips so it's hard to tell but the body is white and there is absolute no soot.

koala

Ethanol fuel seems to be a major contributor. I'm not sure about the USA, but here in Canada, Shell 91 is the only fuel in the entire country without any ethanol added.

That said, I run 94 because horsepower

Jaws1

Rambler_13

My 997.2 definitely leaves a good amount of soot on the exhaust tips and sometimes will spray onto the bumper but it easily wipes off. I had 2 other 991 9A1s but they had black pipes and exterior so I couldn't tell. Other DI cars I've owned have done the same though.

DBH

Just for the record, my Cayman GTS with 9A1 threw a lot of soot out the pipes. I was constantly cleaning them. My current 911 GTS (9A2) has no evidence of soot at all. I don't know why? NA vs turbo?

Rambler_13

I don't think that's the reason, my 997 is turbo.

Rambler_13

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Valvefloat991

DI typically produces more particulates in the exhaust because there is so much less time for the air and the fuel to thoroughly mix. That leaves pockets of slightly lean and slightly rich mixtures. The rich ones produce soot.

As the particulate emissions standards get tougher going forward, it is likely that some DI gasoline engines will need particulate traps in their exhaust systems, much like diesels. This is one reason that some newer engines are employing both port and direct injection on their engines.