haha thats epic !! mine does that too just not as massive, i coast it onto the road before i start it.

ive just got a tune. upgraded turbo. dump pipe tbe, grimspeed 3port and a rough idle for free. and a p0133 CEL

guess ill just have to live with it, not too worried if people say its not damaging anything.

do you find it effects the paint at all ?

 

My 2012 WW GSR get a ton of black soot on the back and its 100% stock. So maybe the color of your car is camouflaging the soot. Whipe your finger after a few days or a week of driving and check it.

 

It might. I haven't really checked up close. But the back of the care gets as dirty as the sides or the front. I get some soot on my exhaust. I havent really seen much anywhere else.

If I wipe my finger across the back of the car and then wipe a different finger across the side of the car will the finger wiped across the back look darker?

 

^This. I use a microfiber fleece mitt for the rear. I also use a detailer spray which just another layer of protection also making it easier to clean the next time.

 

Mine only does that at WOT. If I drive normal there is no build up.

 

Mine is like that, but then again I see my afr at 10s when I beat on it. I got ww also and running Cobb ots map

 

Shows heavily on my WW too, 08's run filthy rich so I expect it. If I can't get to washing it off before it sets, sometimes the orbital is required. But comes off with ease if I have to bring that out.

Hopefully after I opti coat the car it really will just wash off with the water hose

 

There are many factors that influence the amount of carbon and unburnt fuel that can coat your rear bumper. Sadly it's a low pressure area so dirty air swirls around behind the car and that's why it's collecting there.

1) Test Pipe versus High Flow Cat: When I switched to a High Flow cat I noticed a dramatic decrease on the amount of deposits on the rear bumper. The cat tends to burn off excess fuel before it exits the exhaust so if the tune isn't perfect it really does help.

2) MIVEC settings: The more exhaust retard and intake advance you run, the more unburnt fuel tends to shoot out your exhaust. Now the extra spoolup is well worth the trade but if you get too aggressive like right on the surge line of the turbo, expect more carbon on that bumper.

3) The Tune: Closed loop cruising (O2 sensor feedback) should be cycling around 14.7 AFR's and produce very little carbon on your bumper. It's possible that your AFR's are swinging rich to lean a bit more than typical which can throw extra unburnt fuel onto your bumper though. This usually happens with larger turbo cars with bigger injectors and 3.5" MAF's that need better calibration between the MAF and MAP tables to keep "loadcalcs" consistant.

Open Loop or driving at loads of 100+ under boost is where a tune can make quite a bit of difference. If the AFR's are around low 13's at 5 psi and hovering around mid 12's up to 15 psi you will burn about as clean as you can without being too lean. At 20+ psi you will generally want to be mid 11's with a safe tune, although you can be slightly leaner in the 15-20 psi range for a cleaner burn if you spend extra time to dial things in and don't go crazy with the timing advance. For the street that works fine but if you road course the car for 20+ minutes you will have to accept the fact that 11.5 is about as lean as you would want to go and some carbon on the bumper is a reasonable trade for a running engine.

I've actually been black flagged at a road course for too much smoke out the exhaust which basically was from running mid to high 10 AFR's, aggressive MIVEC, and a test pipe. the car ran fine but was just a bit smokey. Follow the above suggestions and it will clean things up dramatically.

 

That's funny.... my garage door has one spot of black soot from my old evo 8 where I would occasionally start the car just before I opened the garage door. Reminds me of that!

 

It may also cause you to carbon up O2 sensors faster, but it's still not a huge deal.

I get some carbon like the OP, but not nearly that much. I wonder if some of that may be coming from the road as well? I know around here they really like to put rubbery asphalt goo into the cracks on the road a couple years after the road was paved. When I drive on roads like that when it's hot out, I see little black specs on the side of the car and on the back. They won't come off easily either.

I can tell the difference between road goo and exhaust carbon, as the road goo is very much like tar and if you rub it with your finger it stretches out and is very sticky. The exhaust carbon spots just come off with your finger, and they aren't as sticky.