as title states, whats are their purpose and is it worth upgrading to an aftermarket one on a sti?

Both are part of the exhaust system.. better designs have better flow.. pretty much it

As with usual exhaust upgrades - you'll get minor responses to flow/response/feel of power.

Heres a pic of an aftermarket up pipe:



And one of the downpipe:

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up-pipe is the last pipe before the exhaust gases go into the turbo.

Unless you have a bugeye WRX (my01/02 non STI) which has a catalytic convertor in the up-pipe, leave it as is.

Dump pipe comes after the turbo and goes down the firewall and under the car. It is worth upgrading this to a 3 inch full turbo back exhaust system.

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RS Liberty - Because WRX's are only good for parts...

up pipe joins the exhaust manifold to the turbo, to feed it spent exhaust gases,
dump pipe takes the exhaust from the turbo to the rest of the exhaust pipe.

Dump pipe is recommended doing as the factory design interferes with the wastegate's (used to regulate boost pressure) flow.

Up pipe should be done if its a bug eye due to a cat convertor being in the factory up pipe that can break down and go through the turbo...

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Balls.

Bugeye STi doesn't have the cat in the up-pipe. Only the MY01/02 WRX. Still can't believe they did that, total bad design ..

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Should have bought an STI

so if i get aftermarket headers its totally different from up and dump pipe yeah?

correct, headers meet the up-pipe.

Do a search and you will find all about them

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Should have bought an STI

headers are as follows :



you can see the difference between std and aftermarket

Note: depending on equal or unequal headers you will keep/lose your boxer rumble.

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worth it get a 3" TBE with a butler dump, imo dont really need to upgrade the front pipe but that up to you as im happy with what i have right now...will sound better and feel more power.

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Biggest gains are had with the design of the mouth of the downpipe. Pay a little bit more and you will get fantastic results.

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[COLOR="Gray"]550Nm off a 2L... Just wish it was in the dak dak...[/COLOR]