My mileage dropped when I installed the 4" Megaflow muff and removed the cat. Not just a little but a lot. From 17 highway to 13-15 empty, worse with load. Today I added a cold air intake hoping for a jump in mileage.
A pal of mine just did same thing to his Duramax with same result.
Any idea's oh guru's of the forum?

 

I certainly don't qualify as a Guru but let me ask you a question,,, did you notice any better acceleration/improved Throttle response??? perhaps it seems like more torque being made????

 

Well I only drove my truck very few miles before the change, so maybe that's it, more power is the trade off. I am looking for more pulling power, was under the impression that the free flow would help with mileage. My pal with the Durmax, did the opposite of me and did the intake first, he noticed better mileage, then did the pipes and lost what he gained.

 

That is the trade off from what Ive seen,,, now that the power is increased you have to relearn new driving habits to keep the mileage per gallon up,,,

When you are making more Power it easy to want to mash on it!!!!!!

I think you will see some MPG gain back with the Smarty Jr. But still a lighter foot will help alot,,,, JMHO and experience with the stuff I'v done!!!!!!

Oh and if you are towing heavy It wont be any better cause you are gonna feel that power and ,,,,, look out!!!!!!

 

Smarty is next on the list. I do have a heavy foot a bad habit I know.
When I had my 2001 F350 with the Nav star, I did the same mods and saw no loss of mileage?? It was the same, but felt more power for sure.
But I only have 12500 miles so maybe she ain't broken in yet

 

I felt the same thing... but I don't remember it being that much, maybe a 1-2mpgs. What I did was put a Aero Turbine XL4040 in the place of the stock cat. It did bring it back up to where it was before, but still had better flow for more power.

 

I removed the muffler, left the cat. My mileage went down at first cause I was stepping into it to hear that nice new sound. After I got over that and drove it normal, there really was not much of a difference. I got my most gains from the Quad box, about 2 to 3 mpgs. Again, it went down at first because I was enjoying the newly added power.

It has been warmer here and I have been running the A/C more, it looks like that is dropping me from 1 to 2mpg. Are you running all the same accessories ?

 

Yea here in Az it's been real hot, so we live with the a/c on, lookin forward to the day we can just open the winows again! I do love the trubo whine, so now and then I open the windows to hear it bounce off the houses. Lot's of a/c loss there!!!

 

That's TURBO, trubo is somethin, I'm always in!

 

From my experience, the air and exhaust mods really don't do much to help mileage or power. My truck dyno'd almost exactly the same as factory stock (280hp/522tq) when I added an AFE Stage 2 air intake and cut out the cat and replaced the stock muff with a 4'' straight thru Magnaflow.

You will prob see slightly better mileage and cooler EGTs if you add the Smarty Jr. (or Sr for that matter).....and drive it normal, which may be hard to do when you feel the power.

My mileage went up a little bit going down from 35'' mud terrains to 34'' all terrains. (narrower tire, less road resistance)

Don't get me wrong about the air/exhaust mods....they sound cool. And prob help a little bit on a heavily modified, bombed truck. But on an otherwise stock truck......the benefit (powerwise) is really minimal, if any. There are other side benefits though...my stock air box/filter would produce about 8 ppm of silicon (dirt/sand) in my oil over a 5k mile run. The AFE Stage 2 filters it down to 4 ppm consistently.

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I think your are dead on. I climbed a long steep hill into the mountains before the exhaust mod, and after and noticed no power difference, lots of noise, scrared the wildlife for sure. I like knowing the intake and exhaust flow free, seems like a way to keep temps down all around. I'll leave it as is. I do want the Smarty jr, waiting for a deal to come my way, seems like I could wait forever

 

I dyno'd next to an identical truck only difference was my intake was stock with an Amsoil DIF and he had a AFE Stage 2.. We dyno'd so close that there was no definate increase from the intake. This was up thru SW3 on the SJR, or about 410 rwhp (corr)...

Thou his turbo sounds better...

 

Nuttin like the turbo sound! I have the K&N set up, because it was cheap.
I must say the instructions and harware left a lot to be desired. It's like they got a deal on nuts and bolts, so you need like 15 different tools to put it on.
My instruction sheet had the wrong truck pictured, but you get what ya pay for I guess.

 

Are you using the K&N filter? If so GET THAT THING OFF THERE!! It will eat your turbo!

 

I hear ya. Well I had dyno'd my truck stock....280/522...on a dynojet then later went to another dyno day event at a different dyno. (mustang) They said I made 330hp. I was jumping for joy! Whoo hoo...I gained 50 hp with only air/exhaust mods.

I got on here bragging about it a few years ago. Some other much more knowledgeable people informed me that had to be wrong.

So I couldn't stand the suspense. I went back to the original dynojet dyno and it made essentially the same numbers as original. Apples to Apples, the air/exhaust mods just don't add power on a stock truck from my experience.

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