I have a 1990 Seville with 4.5L V8 PFI. I am interested in having a custom exhaust installed (flowmasters).

The EGR valve necessitates some exhaust back pressure to function. Would gutting or removal of the cat cause enough back pressure to be lost to cause EGR malfunction? Also, I know the cat and back pressure somewhat has an effect on torque curve. I want to maximize my low end torque (heck - that's what these old pushy rod V8s are notorious for), yet not throw EGR codes but yet allow the engine to breath as best as it can to squeeze as many ponies as I can as well as really give the car a beastly sound.

Recommendations? Has anybody here modified their exhaust on either a 4.5 or 4.9 caddy engine?