Where does the boost gauge monitor vacuum/boost from? Intake side? I was boost at almost 20psi with 2.7 but after changing out cat to a 3" downpipe (I also have a exhaust leak thanks to unaligned flange when welded to downpipe) I see 15psi at 7000+. That's with no boost bypassing and no power loss... So I figure it must be exhaust side.... I'm confused... I know I didn't lose power cause I'm running better times now, and I saw my Airflow on HPtuners run a little leaner and had to up my VE table to compensate. Any thoughts??

 

letting your exhaust breath too much makes you lose boost a bit.

 

I have 3" catless and only get 18.5 psi with a 2.6 pulley.