|Most diesel exhaust systems are single. One pipe runs from the turbo to the muffler and one pipe comes out of the muffler to the tail. Dual exhaust kits for diesel trucks have one pipe from the turbo to the muffler and two tail pipes from the muffler back. Having two huge pipes coming out the back doesn't add any extra power but it sure does look cool.
||For trucks that came with a 3.5" exhaust from the factory (most do) changing to a 4" kit that is bent better and includes a high performance muffler will add power and a performance sound. 5" is over kill for most applications and will have a louder deeper exhaust tone similar to big rigs. For trucks like the 2004+ Dodge Ram that came with 4" exhaust a 5" kit is the way to go.
||Turbo back kits replace the entire factory exhaust system front to back and eliminate the catalytic converter if one exists. Cat back kits only replace the exhaust behind the catalytic converter. Trucks made after January 1 2007 will have a Diesel Particulate Filter (aka DPF) that cannot be removed. Kits for these trucks will replace everything behind the filter and do not include a muffler.