Personally, I have mine routed out the side, behind the left rear tire pointed down at an angle! These are the reasons why!
1. Out the back, the pipes can be packed with mud or dirt backing into a bank accidentally. How many of you been sitting in traffic with that mid 70's to early 80's diesel mercedes benz, and had them gas it to have a big black cloud envelope your trucks front bumper and have it come into the heaters vents!
2. Out the side, if your starting to burn some oil or getting some moisture from a bad head gasket you can see it, generally when driving down the road! By examining your exhaust tip you can tell if your rig is in need of a tune up, or if the carb is running too rich or lean! This is how I found out my head gasket was going bad! Alot of steam coming out of the tailpipe. And what's really cool is watching the flames shoot out of the tailpipe at night when the pipe is jacked with gas.
3. Cut off under the truck can trap the carbon monoxide and cause the metal to rust out. How do I know, just look at the inside of my bed, when I got the truck it had a bad exhaust leak, who knows for how long! The frame has alot of surface rust only from the bed portion back!
