I'm having a hard time getting over 350whp with a 3" magnaflow ceramic cat on 94 pump and S256 turbo. Motor knocks once I get in the upper RPM which leads me to believe that the flow is being restricted/high egt (no gauge just a guess). It didn't do this before with just a straight pipe.

Is this typical or should I re-visit the tune with less timing?

A/F at 11.4:1.

Cheers,
Nate

 

sounds like you need to revisit the tune. cats restrict flow quite a bit at least when i switched from a cat to test pipe it really opened up the car