I was out cleaning the TT today. I noticed that there was a lot of carbon deposit on in the tail pipes. I'm assuming this mean it is running rich.

Where should I troubleshoot first? Will this harm the car running it like this?

Thanks

 

You will always have carbon buildup in the tailpipes and it does not means you are running any richer than you should be. If you have other symptoms such as smoke, hard warm engine starts, etc, then go looking for trouble. Otherwise, drive and enjoy.

 

Turbos, by nature, typically run "slightly" rich from the factory. It is a safety measure so to speak. It's better to run rich as a standard than lean.

Do you have a stock or modified/aftermarket exhaust?

 

Very good to know that it runs rich by design. I don't have any other problems and I guess I was worrying for nothing.

I have a stock exhaust.

 

They run very rich until the engine warms up. If it runs too rich it will throw a code.

 

No, there really isn't much to worry about. Turbo cars are VERY touchy when it comes to knock-count. More fuel - typically - lowers the knock count and/or lowers the chance of knock. There are other factors involved, but typically knock/pre-detonation is curbed via more fuel. More fuel cools the intake charge and helps to reduce exhaust gas temps (EGTs). It's always better to err on the side of caution. Of course, adding a higher octane gas also curbs detonation as well.

There are a few drawbacks to running rich:
1. You won't get the maximum performance that you would get with a perfectly balanced air/fuel ratio given the engine load/rpm/etc. However, walking that line is dangerous as knock is a fine line at times. I'd rather run slightly rich than walk the fine line of perfectly mixed vs barely lean.
2. Your plugs will "foul" sooner. Much like running more lean (turns the plugs white), running rich will "darken" your plugs. Then again, replacing plugs are an easier/cheaper solution than replacing a piston.

Porsche turbos (as well as most turbos sold by manufacturers) run "slightly" rich.

 

A friend of mine tuned his BPU supra (mostly stock) and realized a 10% HP gain at the wheels. He went from 360 to 395.

His fuel curve went down from 12.5:1 to about 11:5:1. Still a pretty conservative setting.