Well. I was in the repair end for 2.5 decades.Modified many cars. I saw fuel mpg increases but not just with a muffler. Lots of these vehicles unless 'other mods' only make more noise.Just my experience. Lots of factory exhaust and intakes flow very well for the h.p. they are.

 

I have been very analytical my whole life......Ran two full tanks before K&N air filter and 18" Magnaflow, and ran two more tanks after the mods. I get an overall average of 3.184 more miles per gallon. Those four tanks I ONLY drove back and forth to work to somewhat insure identical driving habits, duration, and length (no way to be exact of coarse-but a good way to try and eliminate some large variables).
Just numbers, just facts.

 

Not to be argumentative but I've also had K&N filters and catbacks and never did I ever get any increase in MPG. Engines today are finely tuned and controlled by computers and sensors. If you add K&N filter and it allows more air, then the computer will compensate by adding more fuel to keep the desired air/fuel ratio. The O2 sensors and others monitor in a closed loop and provide the engine management module the necessary info. Catbacks or less restrictive mufflers are to far back to make any difference to the exhaust backpressure and exhaust scavenging. I think over time your numbers will return to the numbers before the mods. I wish it was that easy to get an increase of 3+ MPG on my truck.

 

Cai,Full length headers,true duals and then the increases start but even then minimal. But muffler alone or even with a CAI at the most is maybe a 5 to 8 horse gain at peak horsepower etc. Fuel mileage negligible if that.

 

The way to increase MPG and HP over stock is to do the following after you do all of the other mods
1) Install a matched set of fuel injectors
2) Dyno the engine and calibrate the O2 sensors inputs to the computer
3) lean out the factory air/fuel ratio using the Dyno and tuner

 

more exhaust flow= fuel burns easier and quicker

 

OK.... I have a question for anyone in this post who thinks putting on a muffler, or even a cat back, will increase flow resulting in more power and MPGs...

1. What is the MOST restrictive part of a stock exhaust system?

Power (and MPG) is not added by exhaust components, however it can be added with a COMPLETE system. Which is why there is so much confusion on this topic.

Person A... who is a car builder with access to progammers and dynos... I just put on headers, high flow cats and a cat back, also went though 4-5 diferent tunes on the dyno and made 10RWHP and 2MPGs.
Person B after hearing A to person C... Did you hear A put on an exhaust system and got 10RWHP and better MPGs....
Person C after hearing B to D... I "know" this guy who put on a muffler and got 10MPGs and some more HP!!

 

Yeah this will not be won cause everyone will have their own opinion and experiences. I'll check another two tanks in a month to recheck my numbers. Wouldnt more air and more fuel create greater HP and torque? and if it does-doesnt that mean you'll be using the gas pedal less and thereby using less overall fuel?
Check out this link and you can see how restrictive the stock 26" is with pictures of it cut open.
http://www.*********.com/forums/show....php?p=3957068 fill in the * with dodge talk

 

I do not need to look a the muffler, it is not as restrictive as this. Anyone ever see the inside of an OEM CAT? Yes, I know, not a Ram CAT, but they are the same.

http://www.bimmerboard.com/forums/posts/120011

Point is you have an upstream restriction that is holding things up, you can do whatever you want to downstream, but until you fix the upstream with some high flows you will not have any decent benefit outside of nice sound.

 

Only time I got a difference with exhaust was when I put headers and removed the cat and went back into separate mufflers, I don't remember but it was 85 GMC pickup, it gave it a bit of power too, or it could be the noise but when I drove it normal the gas mileage got better.