Bumper turning black ?????

maybe your a/f gauge is off...sounds like you are running rich

Monitored A/F while tunning car on dyno.

a lot of carbon buildup? Put your hand behind your exhaust...see if you get carbon deposits on your hand...then smell your hand and see if you can smell if its lean or rich

It might still be rich. I am afraid to lean it out any more. I have been told I could damage engine due to high compression with forced induction.

well if you hear a knock then you know to stop...

do that hand test and let me know if you get carbon on your hand and what it smells like

O.K. seems we have a carbon problem.

seafoam

Your car is a rich pig. Nothing you can really do about it except lean out your a/f ratio or clean it off with a rag every once in awhile. Don't get a ghey CF cover thing for your bumper exhaust outlet whatever you do though.

how much can I lean it out without damage?

Normal. Happens to me too. You have it tuned rich up top to accommodate the boost, but it's hardly overly rich. Wipe off bumper, resume driving

What A/F are you running with your 10.5 psi pulley?

Exotic II said:

What A/F are you running with your 10.5 psi pulley?

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Right around 12.0 at high RPM's and a bit leaner at lower RPM's, but not much.

Do what I did. Buy a black car.

Seriously, I wouldn't worry about it. The more serious concern is that you aren't running too lean. Just wipe down the car. The exhaust should not be staining the bumper permanently or anything.