Can someone please explain the difference between a down pipe and a test pipe. From what I understand they are identical as far a position in the exahust system but, the test pipe is without a Cat. Is this correct?

 

test pipe is to replace the cat (its basicly a tube that free flowing, u aint gonna pass smog)
down pipe is just the pipe that goes after the cat to the mufflers

so u can have both if u like

 

Would I be correct to assume that a high flow cat is the middle ground between a test pipe and the stock cat it would repalce?

 

actually a high flow cat is a cat still, but sure its in the middle, u still might pass smog with it

 

Then could you explain the physical order of the exaust components from begining to end?

 

you have the cylinders in the engine, the exaust manifold (the pipes from the engine that would be called Headers if all 4 of them were the exact same length), the turbo (if it is turbop charged. if not, just skip this one), the catalitic converter OR testpipe, the downpipe, and then the mufflers/resonator. If you get a system like Borla, you will have a downpipe with it. If you bolt your new exaust directally onto the cat, then you have a downpipe.

 

Much thanks Panda
Much thanks AudiCross

AudiCross, I am not sure I understand what you meant about the exahust manafold/headers. I was under the impression that all manifolds and headers were the same thing. Why would the pipes being different lengths make it one thing but not another?

 

Becuase form the factory, they make the pipes quiet and easy to fit in the engine compartment. in doing this, they wont be the same length. When they are not the same length, then each cylinder has a different resonance and a different amount of back pressure. Also, headers generally have lerger diameter pipes, equating to a greater exaust flow out of the engine.

 

No ****. I find that proves how little I know about this car Do you know what the compression ratio would be for a 1.8t (for the record I did a search but found nothing)? Do other manufactures do this as well or is it limited to Audi?

 

they all make normal manifolds, not headers. but there are some high performance cars that come with them

and the compression ration, i dont knpw. but it would be somethig low. like 8.1:1 or something