Looking at the design of the two DP & stock pre-cat, just with the naked eye one could tell which one air will just flow right threw. The bends in the stock set up as everyone knows force the air to change direction, cause more time for it to release, same as in a hose that you bend, the water moves slower out, right? Where that beer bong you drink out of at the parties goes straight down to your month, allowing you to take in more beer. Straighter the pipe and bigger size ( TT only ) piping more exhaust hp gained. Gutting pre-cats is a temp. fix until you can get the DP. If your looking for max performace and sleep better at night..........
