454 Big Block MPG

[staticattic]

According to my fuel app, I am only getting 5.3mpg in my truck. Yes, I am fully aware of the “if you are worried about MPGs, you shouldn’t have got a 454” argument. I am also fully aware that poor gas mileage is a symptom that something is wrong. I have replaced the spark plugs, ran 2 tanks of gas with fuel system cleaner dumped in, and now i am looking at maybe removing the current carb and replacing it with a new one, although I suppose I could remove the current carb, clean it really good, rebuild it, etc. I am also looking at replacing portions of the ignition system as well. My question is, what MPGs should I be shooting for? I am thinking I should be able to at least squeeze 10 to 12 MPGs. Is that about normal?

 

[Vbb199]

8-10? Maybe 12 at the most.

Kinda all determined by your setup, how you drive.
Im sure someone here will tell you they got 20mpg with x tires, x gear ratio, x carb, x tranny.

What kinda compression is the motor making on all the cylinders?
What condition is the spark plugs in?
They are the most important as you may/may not know. They tell you what sort of condition each cylinder is in

What kinda heads?
Smog? Aftermarket?

 

[yevgenievich]

My 97 one ton big block crew cab was good for 17mpg on highway. But that is with nv4500 and mpfi

 

[SirRobyn0]

5.3 something is wrong. I'd say 10 is going to be the max on 454 but it will depend on rear end gearing, transmission and your right foot. If you were in a 454 motorhome I'd say 5.3 would normal, but your not. Carburetor and ignition timing would be what I'd be looking at. What carb do yo u currently have?

 

[nabeshin]

Are your vacuum lines all old and cracked? If the carb and timing was tuned with lots of vacuum leaks, you'd be sucking in more gas that you should.

I was getting less than 6mpg when I started my journey. It just got 10.5mpg on the last tank, and should top close to 12mpg once I rebuild the carb, idle screws are 4 1/2 turns out; so lots of leaks in the carb gaskets.

 

[Paladin]

Age old question there. Why can't I get a gazillion MPG with a big ass gas guzzling engine? Not trying to be an ass (tho I'm quite good at it) but I think the answer lies within the question!!

 

[staticattic]

Age old question there. Why can't I get a gazillion MPG with a big ass gas guzzling engine? Not trying to be an ass (tho I'm quite good at it) but I think the answer lies within the question!!

i totally agree. i don’t think i am being unrealistic. it is a big block 454 after all and not a prius. if 5.3mpg is what i can expect, then i’ll quit worrying about it. i’m am totally a noob when it comes to square bodies and big, carbureted engines. however, i am not a noob when it comes to engines and engine repair. my VW bugs were carbureted and comparing the two is apples to oranges, but the basic concept is still the same. poor mileage means something is wrong. i was curious what i should reasonably expect that’s all.

 

[ajd89]

My crew cab is a tbi 454 turbo 400 with 4.10s gets 8.5mpg. But I drive it like a mad man. Lol.

 

[nvrenuf]

I had a K10 with a mild carb’d 454, 4spd, 4.10’s and 38’s that got around 10-11 mpg’s on the interstate running about 65 mph. In town it was less but not horrible.

 

[BryanC]

I hate to ask the obvious, but is your speedometer accurate? When I bought my Suburban, there was a 40% difference between the rear end gear ratio and the speedometer drive gears in the TH400.

 

[Bextreme04]

There's definitely a lot that could be going on here. I don't think 5mpg is right unless you are cranking serious horsepower. First, make sure you have an accurate speedometer. Just download one of the free GPS speedometer apps and go on a drive down the highway. You should be able to see how far off your factory speedo is and maybe correct it. If you are actually getting 5mpg, you need to make sure the engine is healthy and free of vacuum leaks. Then adjust the carb correctly once you have made sure the engine and vacuum system is healthy.

 

[broketiredugly]

befor complaining, learn to drive all over again. big motor makes tq, with lots of tq, no need to spin the motor. short shift, get her into high gear as soon as possible without lugging. cruise at 50 to 55 mpg. documemt mpg over a period of several tank fulls. report back.

 

[staticattic]

i use my GPS everyday because it will route me around traffic issues. my speedo and odometer are pretty damn close even though the truck is sitting on 35s.

i do not have 100% faith in my gas gauge. it gets down to ⅛ of a tank and starts bouncing. but what i do know, it is 33 miles from my driveway to work. that’s 66 miles a day and i burn through 12 gallons of gas every day. i work from 0600 - 1500, so i miss most of the traffic both ways. even though the speed limit on the interstate is 70, i cruise between 55 and 60. i don’t do hard launches, i steadily reach my cruising speed and stay there. interestingly, i ran into a dude today in a lowe’s parking lot with a ford bronco on 35s that was sporting a ford 460. i asked him about gas and he said he gets about 10mpg, but he also tows his work trailer.

i already knew i was going to get crappy gas mileage, but 5.3 mpg is pretty low. i am going to take the suggestions provided and run with them and see how it goes. thank you for the ideas and feedback.

 

[shiftpro]

the truck is sitting on 35s.

There's the issue. You would need 4.10 gears. Even though the big block has the torque to drive these meats with 3.73 gears, it's lugging too low in the rpm range and bingo there's a gas station better stop.

 

[HotRodPC]

I was first thinking this thread is like Fire and Ice. Big Block and MPG just don't go in the same quote. But you do have something wrong if 5.3 is all you get unless it's in something like a C60 then I'd say it's accurate and as to be expected. Granted it was with 3.21 rear gears, but I know my speedo and odo were 100% accurate. I don't even think it was off by 1%. My 454/Th400 in a stock height C20 with stock size tires COULD GET 13.2 hwy with cruise set at 65mph on a non windy day and pretty much flat driving. 10.5 was much more common when I wasn't going for the best mpg possible and 8 around town was pretty common without the jack rabbit take offs.