Audi Repair: Audi A6 2.7T quattro, header pipes, catalytic converters

Question
I ask Greg the below question & got the following answerSubject   2000 Audi A6 2.7t Quattro
Question   On 1t starting the car it smokes HORRIBLY for about 15 minutes. It runs great very smooth no miss just smokes. there is no sign of an oil leak anywhere. no problem with power or acceleration after 15 minutes or so the smoking with slow down to just trace amount coming from the exhaust. But shut it off even for 5 minutes & the whole routine starts over again. The smoke is white in color but does sometimes have an a slight oil burn smell Tempature is normal

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Answer   hello
This looks like oil burning. You can check how much oil is inside the intercoolers. You can - remove engine belly cover(under the engine) and you will see intercoolers hoses on both sides. Brake loose clamps on both sides and slide the hose off ---- watch for oil, if there is a lot - you will need that side turbo. Check both sides. If there is a lot of oil - do not wait to replace turbos, because oil is burning inside CATS so after  awhile cat ot both cats will go bad.
Good luck, Greg
MY NEW QUESTION IS WHAT ARE CATS ? WHERE ARE THEY ? WHAT ARE THERE FUNCTION?

Answer
Cats = Catalytic Converters, these are the sections of the exhaust where the exhaust gas is 'cleaned' and these run very hot.  If you check underneath the car, you will see two larger sections just down from the header pipes, these are your 'cats'.  Your engine needs the cats since the mixture is adjusted based on four O2 sensor readings, 2 before the cats and 2 after the cats.  These engines cannot be easily tuned without catalytic converters.  Sounds like you need to replace turbo's though.  Cheers,  Jan