up pipe connexts the end of the header to the turbo exhaust inlet flange.. and the down pipe runs off the other side of the turbo where the waste gate opens too and then down to join to the mid pipe .. which joins to your cat back.

turbo back exhaust doesnt use an up-pipe as thats pre turbo. up-pipe and down pipe together both increase the flow of the turbo.. and let it spool up easier.. for the money i've yet to see an exhaust post better numbers or sound better than scooby sport..... it posts the best low end torque gains of any exhaust I have ever seen..and with the 2.0 in the WRX.. low end torque is much needed....it has gains right across the range of course.. but the low end is pretty bad assed..