When buying exhaust, do I need the purchase the Rear Exit Cat-Back System with split rear single round rolled angle cut tips? What do these tips do?

Also, if I do a test pipe will it alter the sound of the BORLA exhaust system? What will a Test pipe with factory exhaust do for my power?

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03 A4 1.8T Quattro

test pipe eliminate teh Cat there fore higher flow more power, will sound better, but its ILLEGAL, you wont pass emissions, tips are just what you see at the end of the exhaust that sticks out. You can get diff ones for your liking.

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2002 A4(B6) 3.0L Light Silver
Mods: De-badged, Lip Spoiler De-chromed grill
Future 19's, 20%, Lowered

There is no emmissions in the county my car is registered in. It's a rural area.. however I LIVE in a city. That being said, would installing a test pipe on factory exhaust eliminate the need for a BORLA Exhaust system, considering the cost involved?

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03 A4 1.8T Quattro

not if u want alot more power because a the stock exhaust has alot of back pressure and ur turbo doesnt like that so the more u open ur exhaust the more ur turbo can breathe but i think too big changes stuff not surebut yea i have2.5 inchtechtonics with borla mufflers and a 3 inch down pipe and a high flow cat which is legal and almost gives u the same amount of power the testpipe wouldand its awesome. its the best thing ive done to my car i think. other then my brakes

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2005 b6 a4
GIAC stage 1 chip
bilstien pss9 coilovers
evo ms intake
techtonic full exhaust with down pipe and race cat
stratmosphere diverter valve
forge silicon hose kit
brembo 332mm slotted 2 piece rotors with 4 piston calipers

the testpipe will give you the best bang for your buck when considering exhaust components.. the borla will help a little. but not much. it will be more for sound and looks after you put a test pipe in.. the test pipe will give you a little deeper sounding stock exhaust, maybe 10hp on the stock ko3 and a little bit more responsivness(less turbo lag)

but with the small ko3, a big open exhaust is not the best option. it is a small flowing internally gated turbo. it relies on a small amount ofback preasure to build boost.2.5" is the WIDEST you should ever go with a ko3 or ko4 car. and a good HFC like the Labree product will give you a good amount of backpreasure for your turbo...

so if you got the money, and you're not going to go bigger than the ko3 or ko4. then a Labree HFC and and aftermarket catback(including downpipe) that is 2.5" or smaller would be the best setup.. borla is my personal favorite for the sound. very agressive

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yea i loved my borla set up it was the shit, i ran it with a tp too and the gains were real nice

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Richard-
New Beast: 99.5 Ford F350 Powerstroke w/ 07 front, Dp tuned, 5' Exhaust, Big Turbo
99.5 A4 1.8TQM GIAC, Borla Testpipe. Forge 006, S4 Front, C/O's