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Thread: Fuel Mileage extremes

  1. #1
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    Fuel Mileage extremes

    I posting this more to get baseline numbers of what you guys get so I have something to compare mine to, but I typically in my daily driving (north georgia small town mountains, nothing over 55MPH most spent around 35-40MPH) I regularly average between 19.5 and 20.5 (I use the same pump since it's the only one thats ethanol free at the station, fill up around the same time of day and divide miles driven since last fill up my gallon it take to refill till the pump kicks off on it's own, so I have a pretty SOLID reliable grasp of my fuel mileage) but then the other week I drove down to Stone Mountain and back (to get the T/A rear hatch) then I did 1 day (about 50 miles) of normal driving on that same tank and I averaged 26.6 MPG for that tank, now if you factory in my daily driver mileage of 19.5-20.5 for that one day of normal driving then that pushes my PURE HIGHWAY MPG to somewhere around 28-29.5 MPG which is a 40% improvement over my daily driving and that just seams a bit extreme to me, most cars I've had in the past I would see like a 3 MPG difference between highway and city, are these types of numbers what you guys are used to seeing for a mostly stock car? I just feel like my "city" should be a bit higher.

    since the last driving I did that was anything like highway I've done a new fuel pump, plugs, wires, coil packs and installed the rear section (over axle pipe to tips) of a hooker LT1 cat-back, previous pure highway was in the 25-26 range before all this but my daily has remained consistent even with all these updates, is it just the gearing of the 4l60e and 3.08 rearend or is there something that could explain improved highway mileage but see no gains in city mileage (which is mostly country back roads)?

    also with having done all this tune up stuff should I force a relearn by disconnecting the battery (or pulling the fuses, which ever is easiest)?
    Last edited by Daniel644; 05-27-2014 at 01:22 AM.

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  3. #2
    Full Throttle Extreme! Turningfast's Avatar
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    I did math a year or 2 ago and found my mileage to be around 1 mpg wot and up to 30 mpg flat highway rolling at 60 mph. With my current low boost tune, around 15#, and normal for me driving, I average 23ish mpg. I drive mostly highway for work, probably 20 out of the 30 miles per round trip. But, I make sure the car makes some noise at every light on the non-highway part of my commute
    Running turbo car but.......for how long? up to 25#'s so far so good http://fquick.com/1SICK6
    11.63 @118.9 1.63 60' Best trap 119.6
    After almost 30k miles it popped, junk yard L26 going in with a better turbo
    Ooops, I did it again, lol.

  4. #3
    Half Throttle firebird274's Avatar
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    On my Firebird I was getting somewhere around 18-20 city and then about 26 highway, so i dont think your number are that extreme. There was one time that i did get 40mpg on the highway, but that was a fluke because i had a huge tail wind and was on a slight downhill the whole trip.

    2001 V6 FIREBIRD 5 speed
    Mods: Powerdyne with 9psi pulley(currently installed on my work bench), Pacesetter headers, Magna Flow exhaust, MSD coils, 8mm wires, Whisper lid intake, K&N filter, Center Force clutch, and HP Tuners.
    2002 Savana: custom campervan conversion

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  5. #4
    Full Throttle Extreme! Turningfast's Avatar
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    Oops, I forgot my mileage is impossible because I have 80# injectors.
    Running turbo car but.......for how long? up to 25#'s so far so good http://fquick.com/1SICK6
    11.63 @118.9 1.63 60' Best trap 119.6
    After almost 30k miles it popped, junk yard L26 going in with a better turbo
    Ooops, I did it again, lol.

  6. #5
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    Best for me was 33average over a 2100 mile trip, and nowadays on big cam, 80# injectors etc etc, I get around 19 average, doesn't matter highway or city, I drive like an ass everywhere.
    2000 Camaro Y87 3.42s, Built L26, 10:1, ST5 cam, GT35R stock T5. [email protected] RIP 6/21/14.

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    here's some screenshots I grabbed the last time I used the Torque app, it's got me confused a bit, the 99 v6 should only be 3 O2 sensors yet it shows 4 and one stayed pretty constant 0.8-0.7 where the others fluctuated more, do any of you know which numbers correspond to which sensors?

  8. #7
    Light Throttle V6Hawk's Avatar
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    Before the 3.73's city average was 19-22 and highway was around 30. After 3.73's city is around 19-20 and highway is around 26.
    Pacesetter Headers, TSP Rumbler, Highflow Cat, 3.73 Gears, Eaton Detroit Truetrac posi, Transgo Shift kit, SLP Airlid, K&N Airfilter, Free Ram Air Mod, BMR Strut Brace, 32mm Front Sway Bar, MSD Super Conductor Wires, NGK TR55 Plugs, Firehawk Ram Air Hood, Tuned by PCMFORLESS

  9. #8
    (╯□)╯︵ /(.□ . \) Sparky's Avatar
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    My old 98 would do low 20s all city, if I drove like an idiot I got it down to 18-something once. But cruising on the highway it would get 32mpg consistently through the auto trans. Only things I had done to it was a 3.42 rear (which I got a mpg boost out of over the stock 3.08) and a basic tune. Oh, maybe some rust-induced weight reduction helped

    My current 99 will squeak out around 26 highway. Same 3.42 rear axle, but this one is cammed so it is expected to not get the same mpg anymore
    - Jared
    1999 Camaro 3.8L A4. Cammed, so kind of fast.
    2007.5 Silverado LT Z71 5.3L 4x4. Slight lift, bigger-ish tires, not a slouch but slower than the car.


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