Fuel mileage

[67shortstepside]

I have been told that some people are getting around 20 mpg with small blocks with 700r4 trans and 342 or 373 gears . Are any of you guys getting that ?

[GASoline71]

Gary

[randy500]

The mileage they "say" they get and the actual measured mileage often varies....by a LOT

[Greasey Harley]

327, 2jet carb, points, sm465, not sure of my gears.Non ethanol premium.
16 mpg highway. 60mph (steady)
12 mpg around town (depending how I drive)
Smiles per gallon, LOTS 😀

[truckster]

20 MPG, downhill, with a tailwind and a light foot?

Still unlikely.

[Mr Handy]

My math says that with my stock 350 with sm465 and well tuned 4 barrel (wide band o2) and 3.08 rear, I average 16 maybe 17 MPG. If I pop the secondaries I can watch the needle drop.

I will be dropping an NV4500 in shortly and will see what difference an OD makes.
I have also been toying with going EFI so when i do I will see what i get... maybe with all of that 20 mpg would be possible, but I think I would rather a cam and head swap and pick up 50-100 hp instead.

considering the cost of these mods if the goal is to save money on gas, it's a loosing fight.

[toolboxchev]

I gave up on this one a long time ago, the amount of money to be spent to achieve this I might as well buy a new truck and try again

I still want one of those carb fan thingys to spin when I lay on the pedal.

[skytop]

I have a 383 stroker with the R4 trans and I know for sure I am not getting 20mpg except when going down long hills.

[72_swb]

I get a solid 6-7 with a 402 and turbo 400 lol.

[68Stepbed]

My old stock 350 crate engine with TH350, 570 Holley carb, setup got around 12-15 with 3.73 gears, then got about 14-16 with the 3.07 gears.

You should expect somewhere between 14-18 with a 700R4, 3.42 or 3.73 gears and the proper carb.

[weq92f]

My experience...

Recent:

2.80+/gallon...
402, 700r4, 3.73 in '67 C10 = less than 20MPG no matter how/where you drive it.

Long Ago:
0.98+/gallon...
350, 350, 3.73 in a '68 C10 = way less than 20MPG at all times no matter what.


Hth,

-klb

[demian5]

Originally Posted by 67shortstepside

mpg

Not a concern with these vehicles. I would think most are a 3rd or 4th car...

[71cheyennesuperlongb]

My best mpg with a 307,700r 3;08 rearend was17.6 driving so carefully blue haired old laides were giving me the finger! After that tankfull I never checked again.

[72_swb]

Only c10 I've seen getting 20 had a lb7 duramax in it.

[toolboxchev]

I'm putting a call in to my cousin in North Dakota, those boys need to get back to work.

Turn the dam pump on fellas!

[lilred2]

I got 18 on a long interstate trip once with a 92 lt1 motor and 700r in my truck.

[Steeveedee]

I haven't checked around town, since it's pretty much start and stop. When I went camping in February, towing a 6000 Lb travel trailer on the freeway, on rolling hills, and some steep ones, not running the AC, I averaged 7 MPG. Still configured like in my sig. It used to get as high as 13 MPG on the highway with the old shell and no trailer. It's got over 100k miles since the rebuild, so it's gonna get it again soon. I'm not too worried about mileage- it's one of those vehicles that gets driven seldom, probably 3k miles a year. I considered an LS swap, but it will never pay for itself in my lifetime, in the fuel savings.

[tdangle]

70 3/4 ton 350 with th350 trans and 4.10 gears 9-11 city or hwy doesn't really matter. I find it hard to believe it would double with an OD unit. My guess is maybe 14-15 on the hwy.

[special-K]

Why would GM come out with 6.2 diesels if 350s could get 20 mpg?

[Steeveedee]

Originally Posted by special-K

Why would GM come out with 6.2 diesels if 350s could get 20 mpg?

So that they can lay down a smoke screen and keep people from passing them. j/k The real reason is that a diesel has a ton more torque for the same displacement. The higher compression ratio allows a slower burning fuel, so they get better mileage, to boot. It's a win-win. I'd use one, but got sensitized to diesel fumes after years of working on them, and have to make sure I'm not following one, ever. The newer ones using DEF are better, though.

[BROWN 70]

hi guys, 70 lwb gmc. 350/ 350 3.07 rear, camper shell. 4500# 10067353 crate engine, performer, q-jet ,204-214 420 442 cam. best ever on freeway 14 mpg. in town, who knows, lol maybe 8 mpg.

[tutone]

Stock 4 bbl 350 /3ott/ open 3:73 rear. 15 highway @ 55-60 mph all day long

[Fraud]

a stock 350 from 72 or earlier? probably not... especially not if its never been rebuilt

a 350 with well designed alloy heads, highish compression, a sensible roller cam, 93 fuel, fuel delivery and ignition perfectly dialled in, an overdrive transmission, wheels and tyres that aren't too much heavier than stock, a total weight of 4000lbs or less, an attentive driver and a clear highway run at 65mph or less, with no AC.. I reckon you could crack 20...

but no-one builds that sort of motor just to put a sensible cam in it... or drive it carefully, exclusively on long highway runs...

[72freak]

Originally Posted by special-K

Why would GM come out with 6.2 diesels if 350s could get 20 mpg?

Ohhhh my......shall I start? LOL

[72freak]

I have said it for years......if gas mileage is a concern, buy a Honda. I have never had any SBC that did better than 18 with a carb or injection.