I have the Injen straight tip exhaust. Where the 2 pipes don't cross over. Is it true a X-pipe gains more hp? Because of the balance of the gas?

 

in theory.. that's correct

that's why i modded my injen SES by adding an x-pipe, but my motivation was sound... by cross flowing, the exhaust pulses are evened out and you get the nice stock VQ sound back

performance-wise i didn't notice a change... but i didn't notice any difference with any of my mods obviously my butt dyno hasn't been calibrated properly