x and h pipes

The biggest reason for using them is it will allow the use of a less restrictive (louder) muffler and keep the noise level to acceptable levels. If they are positioned exactly right they will help with power but its not a huge amount.

I had a car with duals and glass paks an it was all together to loud and the sound was pretty raunchy under WOT. I installed an H-pipe cross over and the change in the sound level and quality of the sound was dramatic.