After returning from 3 hard days of DE at Pocono, I noticed my rear bumper by the exhaust (not wastegate side) was surrounded by a yellowish brown residue.

I did not notice this after 2 days at Lime Rock last weekend. At first I thought the bumper discoloration was front heat. But when I cleaned the bumper today with OilFlo the yellowish brown stuff came off. What was it and what caused it?

 

Hey, man - by the looks of it, it was probably dust from your old 914...

 

Yellowish-brown residue by the exhaust would suggest a build-up of sulfur. I wouldn't expect this since most commercial grades of gasoline are pretty low in sulfur.

I suppose if you burned enough gasoline and didn't have a catalyst to trap it, you could see some residue - still that is not what I would expect. Did you happen to smell it?

 

I'm not running a cat if that helps support the sulfur theory one way or the other.

Would there be any engine issue that would result in this sulfur buildup?

 

I don't think it is an engine issue - the only other source of sulfur is your oil. What's your oil consumption look like?

I really don't think this is anything to worry about - over time, you may have accumulated some sulfur deposits in your exhaust that under high temperature, vaporized and redeposited on your bumper.