I got a Flowmaster 40 series 3" inlet, dual 3" outlets and it is dumped right behind the cab. The catalytic converters have also been gutted. I eventually want to have it run out the side right in front of the rear tire.
It won't do any serious damage to the engine. I've had it this way for about 5,000 miles now and have had no trouble. It could effect your gas mileage because of the o2 sensor not seeing the voltage it needs because the cats are not there to do their job.
And it did make it louder, but I really don't know how much because the 40 series is loud to begin with and my truck was down for about week and half to two weeks when I did it.
im working on getting my dodge turned in to a extra cab. now that its got a little warmer now i can get going on that and i also have a 71 blazer i put on the back burner for a while a long while. and ow i have my 92 chevy 2500 im working on that i wont to get painted this summer its my tow rig.