flowmaster and gas millage down

[Murphdog660]

i got my flowmaster super 40 in stalled. single 3" in dual 2.5 out. i have a 2006 silverado 5.3 flex fuel. my dash was reading 19 on highway and about 16.5 mpg befor i got my exhaust done. now i cant even get 14mpg on highway. question is is my digital mpg reading correctly or cause more volume leaving making read wrong.??? HELP ME

[claviz13]

Or is it that you like that Flowmaster sound and your right foot has mysteriously become heavier. LOL! Other than that you should pick up a little MPG. Weird.

[KleenZ]

i got my flowmaster super 40 in stalled. single 3" in dual 2.5 out. i have a 2006 silverado 5.3 flex fuel. my dash was reading 19 on highway and about 16.5 mpg befor i got my exhaust done. now i cant even get 14mpg on highway. question is is my digital mpg reading correctly or cause more volume leaving making read wrong.??? HELP ME

Are you referring to your instant MPG reading on your DIC(Driver Information Center)?

Maybe try manually figuring out your gas mileage, then figure out if your exhaust is helping you. I also tended to have a heavier foot when I got my exhaust.

[Daren'z00z71]

Or is it that you like that Flowmaster sound and your right foot has mysteriously become heavier. LOL! Other than that you should pick up a little MPG. Weird.
id agree with KleenZ i just got the same setup as you got today and i know my foot has gained weight, it sounds great

[Murphdog660]

im looking at the DIC and i cant even get 16mpg cruizing at 65. i guess does anybody else have a DIC on the truck and noticed a differnece. what are you guys running as in miles on a tank of gas. do you think the sensor is just reading wrong caus eof more air flow. im alomst used a quarter tank and i got about 75 miles so far. is that good bad or ugly

[Daren'z00z71]

I dont have a DIC but the next time i fill up i will see what i am getting i think i got 11 on the last tank, it might be a while because this week gas has went from 2.50 to 2.89 and i filled last sunday.

[Murphdog660]

yeah that would be nice. also if want try to figure out how many miles you get out of tank.

[Daren'z00z71]

I think i could get a little over 300 miles to a tank town driveing which is around 3 mile trips to school and work. i dont know a whole lot about the gas mileage because i have only had he truck since feb. the last fill up i had 260 miles and was just over a 1/4 tank on the guage 23 gal.

[davzog]

It seems to me that you might have over-scavanged your exhaust...the engine requires a certain amount of back pressure to breath properly. Actually, most factory exhaust systems today are reasonably efficient.

Any time I replace an exhaust system it is because I want to hear the pretty exhaust sound of the the small bolck Chevy engine...nothing much sweeter...

Anyway, simply going to 2 1/4 inch tailpipes could provide the required back pressure to get you back on track.

I had a Ford V10 that would pull like a freight train, until I changed exhaust...I put on a Gibson with dual 2.5" tialpipes, and all my low end torque went away and mpg droped from 12 to 9....ouch.

I reinstalled the stock muffler and went to dual 2.25 tailpipes and everything came right back to normal...I also have over scavaged...go figure.

[Tweeter400]

Reset the mpg on the dic and it will start a new average.
That will give you a more accurate reading. If I remember correct, while the mpg is showing hold the enter button and it will reset.

[Murphdog660]

dang that sucks. i posted about what size to get and everybody was saying 2.5" so i got that. oh well maybe i can live with this for awhile. so your saying by going to a bigger size pipe that why my gas milage went down??

[bizzybone485]

i always wondered this as well. I run 2.5 on my 355 tbi and have only ever managed to get 16 at most on the highway if i was lucky. A buddy of mine had the motor done the same way at the same shop but the only difference was that he had 22s and i had 20s so his tire size was a little higher and he always got better gas mileage than I did. I always blamed it on a possible better tune, my tranny shift kit and my lower tire size throwing off the computer but im beginning to believe that putting 2.25 exhaust is a big deal with these motors. That extra back pressure seems to help out a lot.

[duece325]

just wondering now, i have a 2500hd with a 6.0l (2003) i just bought a cat back from flowmaster, 2.5 in dual and 3inch out with a 4inch tip. is that gonna affect me in a bad way?

[bigolblackie]

When I got my true dual exhaust made last year,they insisted on 2 1/4" pipes for me,Im happy with the results.:cheer: