I've tried two different systems in two years and found no difference in gas mileage. The first was a Magnaflow with duals out the back and I'm currently running a Gibson Super Truck system.
The only difference I've seen/heard is the sound (Gibson is LOUD).
Has anybody noticed any MPG gains when changing out the factory exhaust?
2004 1500qc 4X4 Hemi
K&N drop in
99659 miles and still runnin strong

 

Cat back exhaust is a good thing, but really doesn't do much by itself. I am a firm believer that everything you do to your intake/exhaust system is cumulative.

My truck "woke up" both from a performance and MPG stand point when I added LT Headers to the CAI and Cat Back I already had. It freed up the entire system. I am convinced that putting that piece in, let the other components do a better job.

Your Cat Back would give you better numbers, for sure, but small enough on both the performance and MPG ends that it would be barely noticeable.

Basically, you can enjoy the note of your exhaust, or keep moddin' the whole breathing system for results you can see/feel...

 

learning from school yesterday we talked about most of this topic....
If you want your gas better you have to do what hammer is saying.... you have to work with your A/F ratio in other words improve both sides the intake and the exhaust....
Your exhaust needs to have free flowing so need headers exhaust and keeping the heat in near the engine from the headers will help with the gas as well.... intake side needs to have updated intake of course and you will want some cams for the exhaust and the intake.... more air equals better combustion better cumbustion with little fuel gives a harder stroke.... even after mostly all this though yea it cost alot of money to do alot of this... but even then your maybe gonna add maybe 4-6 mpg if your not a lead foot other wise you just boosted your HP and Torque

 

You'll never get back in saved gas what you put into it, cost wise, in trying to do so. You basically work on performance, the easier an engine has to work, the less fuel you'll use.
I think the best bang for the buck in regards to fuel savings is still an e-fan! The stock clutch fan robs a lot more than most people realize from the engine... It's also a fairly inexpensive way to free up a good, solid 15-18 HP to the rear wheels...

 

yes and no. the biggest restriction is were the y-pipe comes into affect,simply remove the restriction by either going true duals off of the manifolds, or have a larger y installed. what good are headers if they just keep flowing into the y-pipe restriction. its a game of chance when combing intake parts and exhaust parts to make the engine breath better. most catbacks are different in diameter and muffler placement, i noticed that when i switched from my duals on my dakota to a single 3 inch catback, i had way more low end torque getting out of the whole,

 

SD has a point, when looking at your over-all intake/exhaust system, it's important to keep the "chain theory" in mind. You are only as strong as your weakest link. All the money put into better breathing components is money wasted if there is still a restriction that has gone unaddressed...

 

Is there a write up on switching fans? What brand of fan did you wind up getting? Thanks a lot.

 

yes there is, right here

lots of other useful info in the FAQs as weel

 

I put an Aero turbine muffler and kept the rest of the stock exhaust. the mileage seemed to go up 2 mpg into the wind, or against the wind. a very nice deep rumble, too.

 

thanks hammer forgot about the fan part.... even though i was complaining about it today in class.... and yes upgrading anything thats upgradeable in the breathing section of performance will help gas.... aint that sad how it works.... the more performance you have the less gas it uses.... or what hammer said the less the engine has to work the less it uses....all in all your still an 8 cyl and your firing and cylinders are still gonna need the gas and air so your still using them just not as hard if you up grade it...