the engine needs to breathe remove theresonator, put your muffler back on. the muffler is a total a little over 4" discharge, yet has some back pressure if you need more air out remove the cats all of them.
I have with the V8 of course no cats, noresonator, but added 2.5 pipes from engine to 3" from Y on back into stock muffler ,, there are no headers for a V8 in a crossfire so i cleaned out the exhaust manifolds , with tune ,,smaller SC pulley and exhaust i went from 11.87 to 11.49 in the 1/4 mile. Oh it is not that loud as i drive it every day on the street, just a suggestion I would try the exhaust pipes you have now before going bigger jim