forum.audiv8.com Foren English Audi V8 Forum Exhaust, lambda, cats

While I am waiting for an engine to grace my drive to put the car back on the road, there are a few small jobs to sort, and curious questions to answer.

1. X pipe. That's my name for it for now.
Why is there a connection between left and right exhaust, immediately after the downpipes/manifolds?

2. Sensor In the X pipe.
What is it, and it's purpose? Oxygen sensor?

3. Lambda.
Where is it

4. Cats
The right hand cat was nearly non existent, while the left hand was mostly there, but I suspect quite blocked. Will the car require any adjustment to run correctly? There is a sensor in the right hand cat which obviously must be monitored by something.

Hi,

1) X-Pipe is the term we use as well. Why do they cross? Good question, next one please I think it has something to do with the exhaust gas flow...

2) That's the lambda (=oxygen) sensor.

3) See 2.

4) That's the CAT temperature sensor. It controls the symbol in the cockpit instrument (for overheasting). On the ABH it is also linked to the Lambda correction, but not on the PT afair.

Bastian

In Antwort auf:

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I think it has something to do with the exhaust gas flow...

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That's it!
X-pipe makes exhaust gas flow easier at V-engines. In this way, both exhaust pipelines are in use for each cylinder bank.
So torque and power increase while fuel consumption and noise level (inside the) car decrease.
In former times H-pipes were used for this exhaust gas compensation between the cylinder banks. But the 90° angles at the connector between the two pipelines were disadvantageous for an unobstructed gas flow.

A side effect is, that the exhaust gas can flow a little bit better, when one of the pipelines or mufflers is jammed by a burnt CAT.