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.