Hi all. I've finally gotten my three main mods done. I wanted to report back on the 'butt dyno' and the MPG I'm getting on these. All of my MPG readings are based on driving 61mph on cruise control, no traffic. 8 miles out and 8 miles back. I reset the trip computer after the first 8 miles and averaged the two readings. I did this after each of the three changes.

First, I installed a Volant CAI. Very pleased with this one. I like the sound under acceleration, but notice very little to no difference in normal cruising/driving around town. The power increase was noticeable, but not alot. My impression is that the car just runs 'easier'. It feels more free. I'm sure I gained some HP. And that seems to be proven by the increase in my MPG. I started at 17.1MPG based on the car's trip computer. After the Volant, I went to 18.1MPG So I gained 1.0 MPG and can feel the increased power. A good mod.

Next, I bought a Superchips Cortex tuner. I've only tried one of the tunes so far. But this one was a 'wow'. I was surprised how much power I felt after the tune. Acceleration change was dramatic. I used the 'light tow' tune because I did not have 93 octane in the tank and read on the forums that the light tow tune (which only requires 91 octane) was very close to the 93 performance tune. The tune was an eye opener, in combination with the Volant CAI. Downside was I lost mpg. I had thought more HP would mean higher MPG, but not the case (at least with me). I went from 18.1MPg after the Volant, down to 17.0MPG most of the time to get that accelration. It really was a big difference. My wife drove it and came back and told me something was wrong with the car. She didn't know I had changed anything. She said the gas pedal was too touchy and she was jumping away from stoplights too quick! I love it! Thanks Superchips. I am going to try the economy 89 octane tune as well, and see what that does for my mpg.

Third change was adding a 22" Magnaflow muffler. Everyone was saying this will give me a few additional HP and TQ, so was expecting even more jump off the line. Well, I was shocked. I clearly lost torque and felt like just a touch less HP after getting up to speed. My MPG reading backs that up. I went from the 17.0 down to 16.9mpg. Just a small mpg change, but it felt exactly that way. A small loss of HP. The biggest change, though, was loss of low end torque. I'm bummed now. Feel like I spent money to lose power. Any suggestions on what I can do at this point? I thought about going back to the shop that did the install and seeing if there is anything they can recc changing.

BTW, the Magnaflow isn't too loud. Louder, but not bad. I've only ran the car up to 61mph but no drone at that point. I'll be traveling this w/e, so will see if I get any drone above 61mph.

All I can say is, do the Volant and the tune, but forget the Magnaflow muffler! I also called Magnaflow, but they had no suggestions. I told them it had been reported that on our vehicles a Magnaflow muffler should gain around 8HP. They said it was likely more like 3 or 4HP, so little that you'd never be able to feel the difference. But they did say it should be a slight gain, certainly not a loss of power. I'm real tempted to get the Magnaflow cut off and try a different muffler (anyone need a new 22" Magnaflow??... maybe you'll have better luck than I did with it). Maybe the Borla Pro XS? I'm all ears right now. Looking for suggestions to reverse what I've gotten from the Magnaflow. Heck, stock was better than what I've got now.

Give the ECU some time to learn the Magnaflow. I felt the same way when I swapped from a Flowmaster 70 to an 18" Magnaflow. I pulled out of the shop, stepped on the gas, and felt a torque loss. After a few days, I had a smile back on my face.

jb2c...thanks for your update. i was in your same boat however my setup is a bullydog pp wigth and injen, on 22in wheels. i contacted magnaflow to get part #'s for our muffs but after reading ur post, not sure although sudden urges post seems to ease the doubt. you have an 08+ right?

does anyone tried how much mpg gain if go with superchips XSsaver? is there any difference?

i have the bully dog pp, injen CAI AND magnaflow. the muff was the last step i applied in this chain..

the magnaflow DEFINATELY made a difference. i think i had the magnaflow installed maybe two months after i did the power pup and injen CAI, so i knew it was a difference.

im using the premium tune on the pup...

so i agree with urge, let the ECM get used to the air increase and tune. i can attest i felt a difference once the muff was put on... i think i have the 22 inch..

edit: OOh and there are 24 inch wheels on the vehicle...

Urge, I hope you're the lifesaver here! I had not thought about the ECM needing to learn. You're absolutely right. I'm going out of town this w/e, so hopefully that will be enough driving for it to learn the muffler. Sure hope I'm smiling come Monday morning.

Jonah, yes, I have the 08. Hope to report different results come Monday. But Marctronixx says he felt an improvement immediately after install of his Magnaflow. So will just have to see what happens. Would it make any difference if I do a different tune now that the muffler is installed? I had thought about that too.

I have not yet tried the Mileage saver tune, but will next week. Will advise.

i can tell you immediately it felt like i was driving with the brakes on the car before i had this muff installed... once i got it on and drove out the shop, i was like.. dang did i have the emergency brakes on all this time?? :D i mean it was night and day for me. i gave the pedal a little pressure and the car increased in speed easily and swiftly... so yes i felt an improvement...

Good write-up there jb2c

CAI and tune are on my list...

Which is the preferred CAI around here?

Injen CAI + Amsoil Filter...

I finally came down to the Injen and the Volant. Went with the Volant, but it was a toss up decision. I've seen others say the S&B is a good choice. But I think the Volant and the Injen are better looking units, if that sort of thing matters to ya. I'd go with one of those three.

Well I'm very happy to report Urge was exactly right. After my weekend trip, the bump is back. Whatever that ECM did, it leearned well. My power is back, and my mpg is back up. It's hard to describe, but the power feels different now than when I first did the tune. It still doesn't feel quite as 'crisp' to me. But it's so close, it's hard to really say. But the mpg numbers tell me I'm better than I was before. I was only able to check it one way (coming home) so the various variable potentially are there. I want to make my 16 mile route to try to cancel out any variables. But on my way back home, I got 18.6mpg. That's the best I've seen. And that's with the light tow tune on the Superchips.

I do want to ck the mpg on my 'course' and see how it does. I think that will confirm (or not) the gain. That ECM thing threw me, for sure. But at this point, my mods have paid off, and I'm a happy camper. Thanks to Urge for pointing that out. Now if I could find out how accurate that trip computer really is... hopefully alot more accurate than the tire pressure monitoring system.

jb2c,
Good news to hear. I was pricing out an install on the Mag muff and I was getting $200-225, or $35/weld if I brought the muff. What did it cost you if you don't mind me asking. Also, do you know what the part # of the muff? I contacted Magnaflow and I assumed ours was single, but when I looked underneath, I see that its a single/dual. Is this correct?

I'm going to double check the mpg on my little route today. If I confirm the mpg reading, then will try one of the other tunes, probably Mileage saver first. Then the 93 performance tune!

The Magnaflow was, I'm pretty sure, p/n 12580. Yes, it's dual in/single out. I paid right around $100 for the muffler and $40-50 for the shop to install it. They did have to run a little extra piping as the stock muffler was longer than the Magnaflow. One thing I would suggest is to be sure to tell them the reason you're changing it out is to gain performance. I think I may have lost a bit in performance due to not a real good job of welding the muffler in. It does not look like a quality weld job. And I suspect that may be affecting air flow some. If we're trying to gain performance, then there's no point in their doing it if they aren't going to do a good job. I talked with the manager about this beforehand and he knew why I was changing. But I don't think he relayed this to the guy actually doing the welding.

So what was your final result on mpg?

You really should do the physical math calculation on the MPG by filling up at the pump and divide by mileage traveled.

The mpg readout on the dash i believe (someone correct me if i'm wrong) calculates based on the vacuum pressure from the engine and the miles driven.

I'd like to know also what the final mileage was on the Economy tune!

OK, I have finally gotten some results to report on mpg.

I started out at 17.1 mpg highway. Stock. Again, this is a QX56 not an Armada. Confirmed this mpg after many checks and alot of miles. And it was very consistent at that 17.1.

I added the Volant CAI and mpg went to 18.1mpg. Again after several tests, a reasonable amount of miles on the car and it was consistent at 18.1. So the CAI gained me exactly 1.0mpg.

Next I added the Superchips light tow tune. My mpg went down to 17.0. But that was checking immediately after adding the tune, so no miles to allow the ECU to 'learn'. I loved the light tow tune as to performance! It's my favorite so far. But mpg suffered.

Next I added the Magnaflow muffler. MPG initially (without miles on it for the ECU to learn) was 17.0. But after adding miles (thanks again Urge) it went up to 18.6. After more miles, I really think the 18.6 is a touch on the high side. I did not do another controlled run to test it, but in checking on short trips, it wasn't quite as high as that. No official number, just my gut feeling.

Next I tried the 93 Performance (couldn't help myself!!). This one was a real mixed bag of results. And where the confusion comes in. I got 18.4mpg with that setup initially. Clearly had more umph at speed, but also clearly lost torque at take-offs. For my purposes/goal, the light tow is the better choice. But then I ran the route again and only got 17.8. Waited a day or two and tried it again and got only 17.4 this time. So pretty confusing as to what the 93 Performance will get you as to mpg. But since I like the light tow better anyway, and 93 octane is alot more expensive, not an issue for me.

Next I tried the Mileage XS tune. This is supposed to be their best as to mpg. I only got 18.2 and it felt worse than stock as to performance. Clearly not the tune for me.

Next I added synthetics. Mobile 1 in the motor, Royal Purple in front and rear differentials and the transmission. Ran the test and was very pleased to see 19.2mpg. So the synthetics gave me an extra 1.0mpg. I had expected a small gain, but not 1.0. Well worth doing IMHO. Should give me around a 1.5 year payback.

Last, I tried the 91 Performance tune. It worked backwards. It gave me 19.7 on my initial test. I was pretty pleased with this, but both the light tow and the 93 Performance felt alot better performance wise. But to get that much more mpg with the price of gas, I was considering it. Then after putting some miles on it, I ran the route again and only got 18.4mpg. I decided another tune was a better option.

I've changed back to the light tow for now and really like it, since most of my driving is around town and love the torque. I still need to test the 87 octane and Tow Performance tunes and see how they do. And will check the mpg again on the light tow to be sure on that. That's where I'm at for now. Hope myabe some of this can help out. Would love to get that light tow tune torque AND 20.0mpg!!

Did a check on the light tow tune again today. got 17.8 mpg. I'm going to continue checking mpg on the various tunes. Still not sure which I'll end up using. But now that my other mods are done, I'll take my time and check out the various tunes. Anyone else out there that has tried to ck for mpg in a semi controlled manner with the different Superchip tunes?

In the end, I love the light tow tune thus far, so it may be a 'heck with mpg' deal!

Oh, I did check my mph accuracy with the handheld GPS and it was off by .9 mph. I had it sat on 61 and I was actually going 61.9mph. The speedo appears to be correct (as close as you can tell by the needle), but the cruise control is off by .9 (it's digital). I have noticed that these vehicles are pretty sensitive to speed vs mpg. So if you slow down, you will save on fuel. I'd guess that every .1mph of speed would equate to at least .2 mpg difference. Not alot of difference, but with these gas prices still going up...

jb2c,
So good to hear of your results. This has justified my decision on doing the muff swap. However, you have mentioned in a separate post that the diameter size was a concern. I have an 08 Armada. Can you confirm that the correct Magnaflow muffler to use if Mag Part 12580 2.25 In /2.5 Out. What about Mag Part 12588 2.50 IN / 3.00 Out. Several others have installed 12580 which leads me to believe that 12580 is the way to go, but Magnaflow recommended 12588, but he also recommend I go to a muffler shop and have the measure the pipe. I don't have a diameter tape measure all I have is a regular tape measure and I cannot get an accurate reading.

Can someone confirm pipe size or which part# to choose for 08+ Armada?

I'm going by memory here (which ain't what it used to be!), but the 12580 is what I installed. I was surprised to find that it had 2.25" instead of 2.5" pipe. Not sure why Magnaflow would recc 12588 unless the 08 Armada is different than the 08 QX56.

Sorry guys, we all love our SUV's, Im still crazy with mine and would'nt trade it for any other vehicle. I dont think about MPG anymore. I have a few mods and a CAI and if I think too much about gas, I will end up buying a Prius and that is not fun. Very interesting your assessment about fuel comsuption in our monsters. I live in NYC and it is not helpful because there is always a lot of traffic so i usually get 12 or 13 MPG and as i said i dont think about it until i go to the Gas station.