kappa88af

I recently installed a Fister muffler along with a shark werks bypass. I have noticed carbon soot on my rear bumper since the install. Trying to determine why this is and how can I stop it.

DC911S

Carbon soot means its running rich, a tune will lean it out.

John@Fabspeed

Not unheard of when you've eliminated a muffler and replaced the rest with higher flow ones. Less restriction for the carbon to make it's way out the back of your car, same with condensation build up. Every time I start my old Z28 after it's been sitting with straight pipes I coat my garage door and floor with some wet grayness

kappa88af

Thanks for the replies.

Bruce In Philly

Watch your oil consumption. I suspect you are worried about bore scoring and the resulting blow-by.

As you watch, think about ensuring you boil off water in the oil by running the car hot for a while before critical measurement

Peace
Bruce in Philly

gpjli2

Stock ECU usually can compensate for muffler/exhaust 'upgrades'. Not to be an alarmist but soot on bumper is pretty extreme imo. Be especially careful if it is one side. Bore scope is your friend if you have concerns.

CTCOOP

Since reducing restriction in my exhaust system (with Fabspeed center muffler x-pipe) and doing Fister mufflers I'm seeing carbon soot on my garage floor at the rear of the pipes, as well. Nothing on the bumper or anything though. Sound and power is worth it though :-)

Macster

If the engine is running with no untoward symptoms and the CEL is dark the engine is fine and the presence of soot is normal.

Remember too there is 1 possibly two converters (per bank) between the engine's combustion chamber and the exhaust pipe outlets and rear bumper cover. If there was an excess of soot present this could be as much a reflection on the performance of the converters rather than the engine.

For every gallon of gasoline the engine produces around 19lbs of carbon mostly in the form of CO2 but there is some carbon in solid form (soot) produced, too. Every exhaust outlet I see -- mostly my own cars but other cars in parking lots -- are black with soot.

Like I like to remind Porsche owners: Soot happens.

My Boxster doesn't seem to collect much soot on its rear bumper but my 996 Turbo does. Its aerodynamics are better and there is a much more pronounced low pressure area created behind the car -- to help the air forced in through the engine compartment lid exit out from under the car and to help pull air through the intercoolers -- and the Turbo rear bumper cover shows soot. Also, it is hard to distinguish soot from tire/rubber dust of which there is a lot on the roads.

Absent any signs of trouble from the engine or a CEL I'd not worry about a bit of soot on the rear bumper cover.

kappa88af

Thanks for all the replies guys. I think it's just the cost of doing business as many have stated.

Lvt19672

Sooty tailpipes is a warning sign of bore scoring per the experts on Rennlist.

Philster

Post pics. Evenly distributed soot is the lowest of low concerns.

How the tips are positioned can matter. But more likely that some shaking and vibration from the install surely loosened up some soot from the exhaust pipes that stayed put.

If you know what an Italian tune up is, then go forth and do that. If you don't, then shame on you!

(yes, I sold my 911S and miss this placed briefly. lol)

JayRace

Kappa, I will confirm this is completely normal on the 997.2's if you go to a bypass pipe AND use a modified gundo/fister cans. The residue you are seeing was normally caught in the side and center mufflers. I've had this issue on every DFI car that I've substantially modified the exhaust on. Get a good coating of wax on the bumbers and it wipes off easily.

wickerbill

Balr14

My car has carbon buildup on the exhaust tips, too. I have Fabspeed intake and exhaust and custom ECU with a tune. It runs rich for about 30 seconds, when it's cold. No big deal.

swingwing

As you drive around or walk through a parking lot survey the exhaust tips of various cars (even new ones). You'll see soot a lot. Personally I think there's too many reasons to contemplate, but DFI engines, turbocharging, factory ECU settings and even different fuel formulations could be in the mix. I see soot on the rear end of my '09 C2 (DFI engine) regularly and not as much on wife's '07 MB C230 (port injection).