I have a 04 dodge ram 4.7, few weeks ago i put a true dual system on it, but i cheaped out on it and put 12$ glass packs on it, to make it worse they guy who put them on, put them on backwards, to make it louder. I did notice that my HWY mpg went up dramatically, i want from 16 to 22 mpg hwy, and when i went to my cabin, i drove a lot more than i usually do, and i barely ate threw gas. only used 1/2 tank to drive nearly 350 miles.
Any who this is my problem, in city i have noticed a DROP in fuel economy due to the fact that i have no back pressure ( im assuming). And when i drive up a hill, i need to floor it to go anywhere, feels gutless. also its TO LOUD. i like loud exhaust but this is to much.
So im thinking of upgrading to the flowmaster 50 Series. Due to the "increase fuel economy hp and torque" so im wondering, should i get a 2 in 2 out but it wont be "true-dual" or shall i run 2 (1 in 1 out) mufflers and keep the true dual. The reason i ask that is, i want the fuel econ on the hwy, but more power. If i run 2 in 2 out will i loose alot of the hwy mpg or will it stay same, or should i keep it true dual.
There's a lot going on here, lol!
I'm not sure what the difference is with a glasspack and a straight through muffler, I think they are relatively the same. If so, there's no "backwards" way to install as they are reversible. There's no way you jumped from 16 mpg to 22 mpg, 16 mpg sounds about right for your truck.
I believe your exhaust is 2.5" dual pipes into a single 3" pipe. Keep this same size piping, don't go larger or you will lose torque. The back pressure thing is a myth, ignore it. Back pressure is ALWAYS bad for power and torque.
Flowmaster is fine, but mostly for sound. There is very little to no gain in power over oem. I'd recommend a straight through muffler like a magnaflow, dynomax, etc. They will perform much better, still sound great(although different...IMO better), and if you don't want it too loud just get a larger(longer) muffler. More volume = quieter.
Duals is good, but really not any benefit over a good y pipe. Maybe slightly if any. If you do duals make sure to install a crossover, either an x or h pipe. If you don't you will lose power.
I'd also keep as much oem pipe as possible as I believe it is mandrel bent. If you go to an exhaust shop they will install crush bends and perform worse.