The infamous MPG Question

[Col_Sanders]

What kind of gas mileage are you guys getting?

I have an 87 K5 with stock 10 bolts (dont know ratio), 700R4, 35" tires, and engine mods (Edelbrock heads, headers, cam, intake, K&N, dual exhaust, custom chip). I am not 100% sure on what I get, as my odometer is quite a bit off and my gas guage doesnt so much work but I think its around 11-12 or so on the highway and 8-10 in the city. That seems pretty low to me for a TBI. I know the engine mods sure arent helping and neither are the tires (this isnt the most aerodynamic vehicle either )but still think it should be a little higher? I seem to remember getting around 16 or so before all the mods but it has been a few years since I first owned the truck.

I am going to be getting a new 700R4 built next month and will also be buying a 14ff with Detroit and 4.56s. I am guessing that will help in the city but hurt on the highway?

Also I want to upgrade my throttle body but dont know if I should just get the CFM Tech package or the Holley and have my intake bored out. Which one you guys think would be better?

 

[85 Jimmy]

i'm taking a guess at what i'm getting when i say 8 mpg.... but that's with an old wore out 305 that's getting to be embarasing to drive since it smokes soooo much, edelbrock performer intake, performer 650 carb, 700r4, stock 10 bolts with 3.73's, rolling on 35s...

hopefully soon i will be putting in my new 350 and 700r4 with my tpi system and i'll actually find out what kind of mileage i'm getting. i'd like to get around 16 mpg with this setup but i doubt i will

i really don't want to know exactly what i'm getting now, i think i'd die

 

[Thunder]

TBI with a bunch of mods. I average 15-16 city/ hiway. Highway miles are around 18 MPGdepending how fast I drive. I get 17-18 MPG at 75 mph. i get bettr milage if i drive slower ... But who wants to do that? My Engine is built for torque& MPG not HP. It loves to run at 2K RPM.
I have a bored 590 CFM stock TB. Took me a while to tune my engine for it. had to play around with my fuel pressure and timing. but after I got things right i really like it. Nice power gain all thru the rpm range. I like the stock GM TBs They are simple and dpendable.
Dont really like the holly units. IMHO they just suck gas, and dont haul ass. and are a total bitch to tune. Always seem to run too rich.

 

[dyeager535]

First thing I'd say is you need to fix your odometer. Guessing as to mileage is pointless, because typical differences in trucks getting "good mileage" (gas) are usually only 2-3MPG's.

I averaged right around 13 with the truck in my signature, but that is on a bone stock chip that is nowhere near optimal. Plus that included climbing logging roads to the tune of +/- 3000ft multiple times a day, and highway jaunts at 70MPH.

Get into what you can do to improve mileage AFTER you figure out what you are actually getting.

 

[Col_Sanders]

TBI with a bunch of mods. I average 15-16 city/ hiway. Highway miles are around 18 MPGdepending how fast I drive. I get 17-18 MPG at 75 mph. i get bettr milage if i drive slower ... But who wants to do that? My Engine is built for torque& MPG not HP. It loves to run at 2K RPM.
I have a bored 590 CFM stock TB. Took me a while to tune my engine for it. had to play around with my fuel pressure and timing. but after I got things right i really like it. Nice power gain all thru the rpm range. I like the stock GM TBs They are simple and dpendable.
Dont really like the holly units. IMHO they just suck gas, and dont haul ass. and are a total bitch to tune. Always seem to run too rich.

Where did you get the TB? I am thinking about just getting the CFM Tech system or finding a big block one. My odometer is roughly 20% off. I went ~210 miles on 18 gallons. A lot of that was through mountains though. I kept it in OD for most of the trip. the transmission didnt need to downshift for me to keep my 65mph speed going through them. The truck likes going 65 or 75 and up. 70 I get the wobble. I know my speeds based off a friend in another truck.

 

[dyeager535]

Uphill will definitely make a difference. I'd say 11 isn't terrible dealing with hill climbing.

Lower speeds will increase your mileage, 5MPH sometimes means a 10% increase in economy.

 

[ntsqd]

'91 Sub 1500 on 3/4t running gear, ~4" lift. 3.73's x 285/75R16's Stock 700, stock TBI 350 w/ tall air filter can lid & 3" Flowmater(?) cat-back.
Just made a run out to Ridgecrest for the desert race. Drove it to get there & back, not to get mileage. 411 miles round trip w/ ~3500 ft. of gain/loss. 28.9 gallons = 14.2 MPG