I was told this before. Tried it, not the case. My exhaust stops at the front doors. Literally, no more exhaust system after my cat. so I have a hiboost DP and a cat then nothing. With the apex, the length of the whole DP is as long as the HiBoost and cat, then theres nothing after that.
So, the 3in makes my car a HELL of alot louder and backfires constantly it is slower. It takes off harder but after you punch it, nothing. As soon as I put my DP set-up with the cat back on and it's 2.5in. not that it matters, but my car runs good and better again because of the cat. W/o the cat my car is indeed slower. If I had a muffler to give me some backpressure and more piping maybe I could run no cats but as it is now, I need a cat to run this 3in DP.