I have a 2008 silverado that i leveled and put new tires on and now the gas mileage sucks real bad. I new it was going to get worse with the lift and bigger tires but i wasn't expecting 15 mpg on the highway kind of bad!! I was wondering if a CAI or a different exhaust would help much. As of now it is the stock exhaust. Would headers and full exhaust be worth the trouble or would just changing the stock muffler help. Just wondering. I'm open for suggestions. Thanks

 

How big a tire did you go to? Did you change (compensate) the tune for the tires? How are you measuring fuel consumption?

 

I just dont understand why I read so many threads of people getting such bad highway gas mileage. I have a 2000, granted it's 2wd but I get well over 20mpg, with both a 4.8L and now a 6.0L. The newer trucks are more aerodynamic, although I think they do weigh more.

 

I went with the 305/70/18 MT ATZ on the stock wheels. I did not do anything with the tune and i was doing the math when i filled the gas tank up with the mileage and the gallons of gas i put in. Thats how i was figuring it out. I didn't so much trust what the computer was telling me. I figured it would be a little off with the tire size change.

I don't much understand the mileage either. It even has the active fuel management. Granted I know it dosen't do much good when you are going high speeds on the higway.

 

Yeah, your calculated mileage is going to be lower since you didn't recalibrate for the bigger tires.

 

Is there a way you can recalibrate short of buying a tuner?

 

My fuel economy went down 2mpg's with an aftermarket muffler. And, no its not because I wanted to hear my muffler more.

 

you need a tune.

 

I thought that with your exhaust flowing better, the gas mileage would go up?


What kind of tune would you suggest?

 

That's what I thought! I noticed that I did lose some low end torque so perhaps my engine had to work a little harder to get of the line in town. Over all though I can't explain it but I've heard of other guys with flowmasters losing MPG's.