The dip is from the 3 port trying to keep boost up. Its working hard to keep boost level but my head out flows the turbo making it hard to hold boost. I will try a few things to see if we can get it to smooth out.

 

hmmm good to know maybe a 4 port is needed for this setup?

 

A little confused by turn down pipe, is it possible to post pic or example of before & after?

 

After the downpipe, the exhaust is open and pointed down.