Looking for a couple more MPG out of truck. It has around 190k miles. Pull 6-7k trailer a lot. Averaging about 8.5 pretty consistently. Is it worth trying a better muffler? Granted gas is going down, truck is getting some rust, and getting up there on miles. Without pulling around 10. Thanks

There is a fuel economy gain from exhaust upgrades, but it is generally less than expected.

If you are still close to stock,
your exhaust backpressure at
2000 rpm and three quarters open throttle
will probably be
3 to 4 psi at the exhaust port.

About 2 psi of this caused by the catalytic converter, the rest by the muffler and tailpipes.

If you can get this down to 2 psi or less
you might get 0.5 to 0.75 MPG gain while towing.

10 MPG for day to day non towing fuel economy seems low.

Air your tires up to 40 psi, f
ill up the tank with 87 octane "winter blend" gasoline,
then drive 100 miles at a steady 60 mph
on a blacktop interstate without super steep hills
during a day when the wind speed is less than 7 mph.

If you do not get at least
17 MPG
there is something else wrong with the truck,
such as a poisoned oxygen sensor
or a fuel injector(s) dribbling fuel when it should be off.

With all due respect, I am not convinced you will see 17 mpg out of a 04-08 3/4 ton 4WD Hemi even under your testing conditions, at least not with the 545RFE. There are a small number of MT trucks out there that might do it, but I still doubt it. And if I was to run that test, I would put a full 80 psi in the tires....

I agree that exhaust changes don't make much of a difference. Maybe with the full JBA set up, but the cost would swallow the increased mileage savings such that I doubt you would reach a positive ROI. I have the cat back set up on my 05 QC 4WD Hemi. It is lighter and sounds cool, but that is about it.

The only thing that seems legitimately reported to increase mileage are the hub conversion kits - spyntec, dyna-trac, etc. Again, the cost will far exceed the savings, but there are some other benefits. I am looking at these now.

Thanks for replies. I agree 17 is not even close to reality. I do have some Mickey Thompson aggressive tires on also but keep them at 60 PSI. It is a big, tall, heavy truck but would like a hair better MPG. It was just at shop getting new water pump and tstat. I should have had him check o2 sensor. No check engine light ever on.

I was talking to an older guy with a Ford Super Duty V10 said he picked up 2-3 with muffler swap. I know apples to oranges.

Iowa is all blended crappy Ethanol gas, so that does not help. Unless u want to pay extra .30-50 a gallon.

Can I pull cat off or is there a o2 sensor after cat? not worried on emissions.

Not going to mess with hubs or full on exhaust.

I did the locking hub conversion on my 06 2500 QC Cummins truck and only got about 0.8 improvement at best. Not something I'd spend over $2K on again.

I put a Flowmaster cat back on my 05 1500 HEMI quad 4x4, replaced the awful factory y pipe with a Magnaflow one and put on EBay Chinese shorty headers and got a nice performance boost. I never tested mileage but I didn't notice any obvious difference. These things cruise at 1700 RPM and probably only 25-30% throttle opening, I don't think you'll find much of a benefit mileage wise, BUT it's definitely worth the performance increase (0-60 in the mid-high 7's with mods, vs low to mid 8's stock), and I don't even have a tune yet. Honestly, if I had to do it again, I'd replace the factory muffler (the stock pipe is 3-3 1/2") and do headers and a y pipe. I read on a Ram forum someone dyno tested the y pipe mod and it alone was worth 8 hp (Did I mention the factory one is horrible?). The factory Y pipe on the new rams is even worse, I checked out a 2015 Ram 2500 Power Wagon and the one pipe going in is basically flat.

Good point about the y-pipe. It is ridiculous. Crushes the pipes in half (picture).

At Guitar - when you are only getting 12mpg, that .8 is still almost a 7% improvement. I think the passenger unit bearing on mine might be crapping out anyway. outside of tire on that side is wearing....

There are o2 sensors after the cats. Remove them and it will throw codes. I am not convinced you will see a mileage increase either.

Header choice on the 2500s is pretty limited.

The year they abandoned the CAD (central axle disconnect) Chrysler put out a press release that it was costing 1 MPG

If your tires are really bad rollers,
it is possible that you would get less than 17 MPG on a 60 mph test run.
SIXTY Miles per Hour.
60 mph can be easily checked because ten Interstate mileposts should go by in exactly ten minutes.

For testing purposes you can narrow down whether poor fuel economy is being caused by the engine or the drivetrain/body by coasting down a hill and seing what your "terminal velocity" is by gravity alone.

Many "steep" hills on Interstates leading down to river bridges are 4% grade.

On a long four percent grade hill a 5400 lb 2wd Ram with Bridgestone Deuller HL 245/70R16 tires will coast in neutral at approximately 70 mph on blacktop, and slightly higher on concrete pavement.

A rough way to test engine efficiency is to idle the engine without the AC on for a long enough time to measure how much fuel it uses.

A 1995 Magnum 5.9 V8 idling for three hours will use 2 gallons.

A good condition 2004 5.7 Hemi will probably use less than 2 gallons.

I would say those tires are your biggest problem. The width for increased drag and especially the height is killing your overall ratio and making the engine work harder.

Not much you are going to do unless you change the tires to back to a stock height. Then only help some, but that engine has enough power you probably don't even notice it is laboring with the increases in ratio.

Well, tires are stock height but aggressive. I love them and they dig, never spin out pulling boat off ramp, snow and mud they are at home. Howl a touch but worth it.

I ended up hacking off muffler and Y-pipe right after cat. Hacked off exhaust I put on my 1990 dodge 1/2 ton 4x4. It was full 2-1/2" with dynomax bullets and homemade Y-pipe. I ran for a few weeks before rolling truck.

Anyway, I got it all together with some slight mods. Used factory 3" tailpipe. It has a little more low end from just a few miles driven. I little noisy, but sounds good. Filled it up and will see what it does.

Well I have not picked up much, if any mpg. I do a lot of short trips and stop go with trailer. It does sound nice, maybe that is why it is not getting better mpg with my foot on the gas more.....heh

There is only one way to get better fuel mileage from any 3/4 ton 4x4 truck with big tires- don't start it up. I'll never understand why so many people insist on owning these things (of all makes, not just Dodge) and then complain about fuel economy.

What were you thinking when you bought it?

If you need a truck for a daily driver, you will have significantly higher gas expenses than if you do not.

If you need better fuel economy, you will be significantly limited in what you can tow and haul.

Always, and without exception. Decide what you need for most of your use, and compromise accordingly.

Yours sounds pretty typical. On average I`m getting about 10-11 mpg on my 06 2500 4x4 5.7l. I have seen as high as 14 mpg on highway. While towing a camper about 8-9 mpg. I will be changing my muffler soon with a performance one. Mostly because the old one rusted out. BTW, I don`t see him as complaining. Just asking a question.

If you want a point of comparison, this is my truck:


2005 hemi 1500 4x4 short bed standard cab. short, but heavy

3.92 rear end, with the 20" wheels. 275/60 R20 I think they are. pretty tall. not huge

With a mix of city and highway driving, the vehicle has a lifetime mpg average of 14.4 according to the computer. so I wouldn't expect higher than 14 with a 2500

I put 17" steel rims and snow tires on mine and it scares the hell out of me to drive. like piloting a dingy in a hurricane with that hard compound

I will say this. even with the big stock wheels aluminum/flower petal wheels, on a cool autumn night, it will lay a serious patch without torque braking. And that's with limited slip diff. I was impressed by that.

Heh, yeah I was not expecting the mileage of a Prius when I bought it. But, I will not go back to a 1/2 ton after having a 3/4, pulling as much as I do. Oh, it is a 4 door also.

The Mikey Thompson's are getting down there in the tread department, but they got grip. Although, gravel roads and heavy loads don't mix well with them. Probably need a new set this fall. What do you guys run that hold up well to heavy loads? I don't care about ride quality.

Not a daily driver but, it is truck and is used like one. More than most of the other clowns with a 7" pipe blowing black smoke out of it....

Check this article out, same truck, just different tires and a 2.5 mpg difference

http://www.fourwheeler.com/how-to/wheels-tires/129-1104-tires-and-fuel-economy/