I`ve had a MRBP catback for some time and just added the Edelbrock shorty and then I got an unwelcome vibration from the resonance at 4K. The original cat had the guts knocked out so its like a straight pipe. Could not stand the sound and vibration so I had a high flow cat installed where the flex was and the flex is now under the oil pan. It is a nice sound now with less vibration and resonance, but some remains. The installer said the high flow cat would be better than a muffler to quiet the car because its more dense and no room to fit a muffler. If you still have the original cat your results may differ.
H & R springs, Addco rear sway, frt & rear stress bars, s/s brake lines, adj. KYBs, Short air ram, UDP, shift kit, Hawk pads, speed bleeders, Torsen , Fidanza flywheel, MBRP catback, TB, SVT header