Who gets the best gas milage

[78GMC SIERRA CLASSIC]

I was just wondering who gets the best mpg from there 350 sbc I get about 10-14 guessing with 4wheel drive and 33s
And what have you done to get such good milage

[Chionos GMs]

Whats is done to your truck?? My ol 305 did about 10 and its a 2wd

[joe231]

I put TBI on my crew and have been getting 13.5-16.5MPG since I started driving it.
It has a gm crate motor and a 700R4
I am going to swap rear ends in the next week or so and hope it helps my mileage a bit more.

[cableguy0]

If your getting that kind of mileage with the rear you have now I wouldnt change anything. You will likely hurt your mileage if you go too high with the rear. The rpms will be too low and the engine will lug itself or search in and out of overdrive.

[joe231]

Originally Posted by cableguy0

If your getting that kind of mileage with the rear you have now I wouldnt change anything. You will likely hurt your mileage if you go too high with the rear. The rpms will be too low and the engine will lug itself or search in and out of overdrive.

You are correct, but have it backwards. It currently has 2.56-2.73 gears and turns very low RPM @65. it lugs down and any time you give it any throttle it down-shifts. I'm not going higher, I'm going lower. I plan on running 31" tall rear tires with 3.73 gears and should be turning @1800 RPM while cruising @65MPH. I hope the less down shifting, cruising in a better power range, and no more lugging will equate to a little better mileage, if I can keep my foot out of it

[cableguy0]

It will definately help, im surprised it even gets into overdrive with only a 2.73 gear. I assume its pretty flat where you live too.

[joe231]

Originally Posted by cableguy0

It will definately help, im surprised it even gets into overdrive with only a 2.73 gear. I assume its pretty flat where you live too.

Yeah it is pretty flat.
Any little incline or over pass will kick it out of OD. Even while I'm in OD on the flat freeway the truck will slowly lose speed until I have to give it more throttle to get it to kick down so i can get my speed back up.
The PO put the OD trans in and i guess he didn't realize it needed different gears.

[Chionos GMs]

If my old 86 had a 700r4 I would kept it and fixed the bearings.

[OleBlue79]

My 79 C-20 with a 350 CI, TH400 and 3:73 gears gets 12MPG. I don't have a tach but it gets wrapped up pretty tight on the interstate. I usually try to go only around 60 or 65 MPH.

[S10Fan]

My 3:42 rear, 454, 700R combo gets 28 miles per 2 gallons. LOL.


14 mpg highway no matter what I do. I have a brand new Richmond 4:10 gear I'll be swapping in pretty soon that should help bump up the "around town" mileage.

[jake wells]

i got 11.2 mpg driving home from the dealership
its a 77 gmc 1 ton dually it has a 454/th400
not to bad pushing a 1 ton brick down the road going 65.

-Jake

[Fixwhataintbroke]

Originally Posted by jake wells

i got 11.2 mpg driving home from the dealership
its a 77 gmc 1 ton dually it has a 454/th400
not to bad pushing a 1 ton brick down the road going 65.

-Jake

Dang that's better than mine, i only get 8 to the gallon....454/th400 also..

[joe1982]

solid 10mpg with my setup!haha

[jake wells]

Originally Posted by Fixwhataintbroke

Dang that's better than mine, i only get 8 to the gallon....454/th400 also..

hard to believe but the secondary's are disconnected
and its going to stay that way.

[OleBlue79]

Originally Posted by S10Fan

My 3:42 rear, 454, 700R combo gets 28 miles per 2 gallons. LOL.


14 mpg highway no matter what I do. I have a brand new Richmond 4:10 gear I'll be swapping in pretty soon that should help bump up the "around town" mileage.

That's the funny thing about big blocks. They get what they get, no matter how you drive or anything you do to try to help it out.

[Benelli]

I get like 7.5-9 with my 350 w/ TH350 and 31" tall tires. Glove box says 3.40 gears, don't know if PO changed them out though.

[Ralph_Dogg]

how do you figure out your gas milage, cuz i can estimate about 10 miles one way for me... what size tanks is in these dual tank trucks...??? im probably getting horrible gas milage... is there anything you can do to improve it a lil bit...???

[78-5.3]

over 20 mpg 5.3 4l60e 2.73

[bikes&bowties]

350/sm465/3.73'/4x4/35's= Im getting ****ty mileage...

[Driveway Dreams]

I have a 350 w/ a granny low manual, 2wd. I get 8-10 mpg. I tac out about 2800 at 65 mph in final drive gear. That gets annoying.

To figure your mileage, start with a full tank. Write down your starting miles at that point. Drive the truck till you put gas in again. Fill it back up. Figure out how many miles you have gone since the last fill up. Note how many gallons you put back in. Divide the miles by the gallons.

Ex: 150 miles/12 gallons=12.5 mpg.

Just remember, miles divided by gas used gives you miles per gallon.

[blakeduren]

Of course, if you have anything but STOCK sized tires and a STOCK gear ratio, the speedometer and odometer are NOT accurate at all. (You can do a percentage thing and guesstimate for the changes, but that is only so accurate.)

I will guess that most of us have changed one or both of those things in our trucks...

[BIGCHEVYMAN]

14.5 every day driving.
16 on the interstate.
that is with a 89 crew cab 4x4 with a 6.2 diesel and a sm465 4 speed.
i wish i had overdrive.

[gchemist]

I'm close to the top of the list with HP and MPG. ZZ4 stock 355+ HP. I have a ton of changes to my truck from engine, exhaust, body and bed cover.
13-15 mpg city
18.5+ @ 70 MPH 700R4 255/60R15 tires 3.08 gears turning 1950-2000 RPMs. Oh, on a carb too!! If I slowed down to 65, I could probably hit 19-20. Get this, almost identical to the old 305!!

[piecesparts]

I just did 3000 miles on the Hot Rod Power Tour with mine (see avatar) and it averaged around 15 MPG with a 383 stroker engine, 700 R4, 3.73 posi and 28" tall tires on the rear.

[86swb]

I get about 15 MPG on average with my 350 engine, 700R4, 3:73 Eaton posi real.