Terrible Fuel Mileage

[03f250stroke]

Hey whats up guys, I have a question for you, I called Raul, who BTW kicks A$$..and is probably super annoyed that I call him at least twice a week with questions but always is nice and helpful. Alright here is my problem. I lifted the truck as some of you may know. put a set of 35 pro comps on there. I have an SCT looney, 4inch straight pipe. and an intake. The truck is great runs perfect everything seems ok. I calculated my fuel with the new tires I got a killer 11.7 MPG. Alright let me state a few things first. I called Vivian and retuned for the bigger tires. I added shims on my driveshaft. And I havent been getting on it alot either. I still need an alignment but dont think that affects anything. I want to say though. I felt that my trucks mileage went down hill after I pulled the cat off. Raul and I both felt that the 6.0 needs the back pressure. I 100% think so especially for a lower HP 6.0. I am up for a oil change in the next like 200 miles. I have 70k on it right now, I am going to do the fuel filters and water drain. Tomorrow I am gonna throw the cat back on and put a economy tune on there. See if that does any good. What do you guys think I should do on top of that. Like i said the truck doesnt perform any worse but, Ive had the SCT on my truck after having it for less then a week and its been on Looney since day 1. The exhaust went on 2 weeks ago and the lift went on last friday. I honestly think its the Cat and the bigger tires. I can deal with 16 but 11? thats insane I sold my v10 for a 6.0 in hopes of getting better mileage. with the looney I got almost 20 sometimes with stock exhaust. Please anyone shed some light on this problem and help me get my mileage back lol

-Evan

[Clay Henry]

you have 35s, you are running looney, you aren't going to be gettin great milage...sorry to tell you.
The exhaust doesn't make any differnce in milage. The biggest thing is intake temp and winter mix diesel fuel. When its cold, you will see a decrease in milage from the temp as well as decreased milage from winter mix diesel fuel. You have an 8,000 lb truck (+/-) and its gonna be hard to get more than what you are getting with what you described under winter conditions.
I drive at 60 mph as often as possible and i get 15 mpg...stock wheels and tires and no looney tune.

[planeoldguy]

OK, I'm keeping my '01 350 stock, 19 is nice.

[03f250stroke]

I hear ya man..The thing is though that my dads truck has a straight pipe exhaust with the cat on there..no tuner but does have 33s..no effect in mileage at all..his truck is also a 6.0. if anything it probably got better. I understand bigger tires they are heavy. Totally understandable. but 11? that is like criminal. and what is this mix diesel? And thanks for the info I didnt know all about the winter conditions changing my mileage like that. starts to make sense..at least its making me feel somewhat better. thanks alot man

-Evan

[LvTitan]

okay...
if you are running winter fuel then you will lose mileage. if you are running larger tires you will lose mileage. If you are stock, then you will probably wanna keep your cat, but since you are running the looney tune, you will not suffer by removing the cat. you are probably putting your foot in it more than you think due to the newfound power and sound from your mods. make a conscious effort to drive easy and see how much mileage you can get out of it.
my truck is lifted on 35's and i never see more than 15mpg on the hiway, and usually about 10-12 around town. you own an 8000 pound diesel truck you cant cry about mileage man.

[03f250stroke]

ohh easy man im not crying about it. My questions were simple. I thought Im having a different kind of problem. Im not too worried that my fuel mileage is low in that aspect but the fact that its low maybe due to something else. but last week i was getting 17-19 with a looney and straight pipe. I put 4 more inches of tires on my truck and it drops to 11? 15 highway isnt bad, around town though is mainly my driving so idk..i love the lift but i wish there was another way around it. I appreciate your help in trying to make me understand. I mean everyone on here is more then nice believe me. Ive been on some real bad forums where if you weren't there from day 1 you were beat. But either way my concern was more then my mileage but worried me that I may need to be looking into something else.

-Evan

[Builttuff]

Originally Posted by CHenry

you have 35s, you are running looney, you aren't going to be gettin great milage...sorry to tell you.
The exhaust doesn't make any differnce in milage. The biggest thing is intake temp and winter mix diesel fuel. When its cold, you will see a decrease in milage from the temp as well as decreased milage from winter mix diesel fuel. You have an 8,000 lb truck (+/-) and its gonna be hard to get more than what you are getting with what you described under winter conditions.
I drive at 60 mph as often as possible and i get 15 mpg...stock wheels and tires and no looney tune.

I dont think that winter fuel would have any affect on milage like it used to. I used to Haul fuel and when a customer wanted winter blend I blended no. 1 and no.2 fuel up to 65% no. 2 35% no.1 plus added an additive. Now that sulpher is the issue I dont see them adding no. 1 like they used to. No. 1 is high in sulpher, usually around 800 ppm. Ultra low is around 10 ppm.

I know there is someone going to argue with me here so before you do my info comes from being around petrochemicals the last 11 years. I hauled it for 7 years everything but propane. Ive been at a petrochemical co. for the last 5. I run tests on every fuel that comes up the line, sulpher,vp, distilation, conductivity, flash points, so thats where I get my info:-)

[Dave]

The taller tires killed your mileage. Also your odometer is incorrect unless you adjusted it with the SCT so your mileage calculations will be off. If you want mileage back you have 2 options. spend about 2k and have your truck regeared, or put the smaller tires back on

[03f250stroke]

Originally Posted by Dave

The taller tires killed your mileage. Also your odometer is incorrect unless you adjusted it with the SCT so your mileage calculations will be off. If you want mileage back you have 2 options. spend about 2k and have your truck regeared, or put the smaller tires back on

thats the reason I went with the 4inch lift as apposed to a 6 or even an 8. I wanted to stay with 35s. I talked to alot of guys and they said anything over 35 you need to consider regearing. I mean if thats what it comes down to. 2k for new gears wont kill me but seeing my needle moving like a clock does. If some1 else can share some more info that would be awesome. Im due for an oil change and I want to change my fuel filters as well. Im thinking maybe that has something to do with it. But then again the truck runs perfect. I also thinks its the cat. Im gonna put it back on and see what happens. see where that brings me

-Evan

[Dave]

Did you recalibrate your speedometer and odometer to the new tire size?