Miles per gallon (MPG) Truth or myth?

[ktztrk]

I have heard that our trucks give low miles per gallon, even when stock and carb is tuned well.
I have a 1970 C10 350cid with turbo 350 transmission that burns the fuel very cleanly, has great pickup and gets only 13 miles per gallon.
The only problem I have is the kickdown does not engage. I don't normally need it or use it, but am working on getting it fixed.
Is the low gas mileage the truth or a myth?
P.S. I switched to a Holley 4360 Economaster carb from the stock Rochester
Quadrajet.
Any clarification greatly appreciated.

[Longhorn Man]

here is a poll I did right here on this board... all engines, all trannys included as one group number.
http://67-72chevytrucks.com/vboard/s...d.php?t=172346
I have found that with a 300,000 mile worn out 350, a semi worn 400 small block, a hopped up high compression 350 with too much cam, and a caddy 500.... ALL got me 10 - 12 MPG on average in 3 seperate trucks. (the cammed out one lived in 2 seperate totally different trucks too)

[BarryB]

I know of a 71 Short step. That gets 30 mpg. Stock motor, and trans. Of course this is a 250 6 cylinder and 3 spd trans.

[blaserman]

Take mine

[junkyardjohn]

Yep 13 Isn't All That Bad For These Old Trucks. nobody Ever Underestimates Thier Trucks Horsepower Or Gas Millage. I Have Replaced Many 6 Cuy.s With Big Blocks Without Seeing Any Big Change In Gas Millage. Theres Always Somebody Who Know A Friends Cousins Neighbors Nephew That Gets 30 Miles To The Gallon In One These Trucks Stock. Well After Owning & Driving More Than 20 Of These Trucks Since 85, That All Got Between 10 & 13 Mpg.. I'll Have To Call Bullsh!t Till I Can Be Proven Wrong. I'd Love To See It Happen, But I'm Not Sure It's Possible Even With A Cummings Turbo Diesel & A 6 Speed. John

[cdowns]

these trucks were made when gas was way less than 50cents a gallon(i remember buying gas the late 60's at 15cents a gallon) and nobody ever talked about gas milage or prices much less being a news story on tv // gm ford and chrysler did nothing to design for gas mileage ,any vehicle from the 60's thru early 70's that got good gas mileage was purely accidental/// 10mpg back then was quite acceptable mileage

[panhandler62]

You could probably get decent milage (low to mid 20s average) with a modern drivetrain but the best engineers in Detriot are having trouble hitting 30 even with hybrids in fulkl size trucks.

You might reasonably expect to get low 30s on the open road with the right setup though. My 95 Z-28 got about 32mpg once on a trip to Florida cruising in 6th at around 65 -- still only averaged about 13 in normal mixed driving though.

[junkyardjohn]

Originally Posted by panhandler62

You could probably get decent mileage (low to mid 20s average) with a modern drivetrain but the best engineers in Detriot are having trouble hitting 30 even with hybrids in fulkl size trucks.

You might reasonably expect to get low 30s on the open road with the right setup though. My 95 Z-28 got about 32mpg once on a trip to Florida cruising in 6th at around 65 -- still only averaged about 13 in normal mixed driving though.

& I HAD A 750 YAMAHA THAT GOT 70 MPG, BUT THIS IS ABOUT GAS MILEAGE IN A STOCK 67-72 CHEVY TRUCK. YOU CAN'T REALLY COMPARE THEM TO OTHER VEHICLES, OR ELSE PEOPLE WILL START COMPARING THEM TO HONDA'S OR TOYOTA'S. LOW THIRTIES IS A "REASONABLE EXPECTATION" ONLY IF YOU'RE SMOKING CRACK. THESE OLD TRUCKS ARE ABOUT AS AERODYNAMIC AS A BRICK. SORRY BUT IF GAS MILEAGE IS A MUST HAVE... WELL YOU WON'T FIND IT IN THESE OLD TRUCKS. JOHN

[jimmydean]

I sold my '75 SWB GMC 4x4 that averaged 8 for a Honda CRX that got 45. But that winter the Honda was stuck in the parking lot for 3 days waiting for the driveway to melt.

I look forwrd to converting my rig to E85. I may still get only 14 mpg, but at least 85% of it is renewable.

[Joe67]

Considering the 505 HP 2006 Corvette Z06 is getting 26-28 MPG on the highway, I'd say GM is getting damn close to 30

[panhandler62]

Originally Posted by junkyardjohn

& I HAD A 750 YAMAHA THAT GOT 70 MPG, BUT THIS IS ABOUT GAS MILEAGE IN A STOCK 67-72 CHEVY TRUCK. YOU CAN'T REALLY COMPARE THEM TO OTHER VEHICLES, OR ELSE PEOPLE WILL START COMPARING THEM TO HONDA'S OR TOYOTA'S. LOW THIRTIES IS A "REASONABLE EXPECTATION" ONLY IF YOU'RE SMOKING CRACK. THESE OLD TRUCKS ARE ABOUT AS AERODYNAMIC AS A BRICK. SORRY BUT IF GAS MILEAGE IS A MUST HAVE... WELL YOU WON'T FIND IT IN THESE OLD TRUCKS. JOHN

I was only using the Z-28 as an example to illustrate that the milage you get in ideal conditions (very low rpm at median speed with little to no acceleration) does not mean your "real world" average per tank is anywhere near that high.

[nate68]

aerodynamics and weight are what kills it for trucks. i bet these would score terribly in a wind tunnel test.
you can lightened the truck up a bit (or a lot), put an efi and OD trans.
i've always wanted to see a car magazine do a project to see the greatest mpg they could get out of a classic car/truck and still have decent performance.

[TP from Cntl PA]

Originally Posted by junkyardjohn

Yep 13 Isn't All That Bad For These Old Trucks. nobody Ever Underestimates Thier Trucks Horsepower Or Gas Millage. I Have Replaced Many 6 Cuy.s With Big Blocks Without Seeing Any Big Change In Gas Millage. Theres Always Somebody Who Know A Friends Cousins Neighbors Nephew That Gets 30 Miles To The Gallon In One These Trucks Stock. Well After Owning & Driving More Than 20 Of These Trucks Since 85, That All Got Between 10 & 13 Mpg.. I'll Have To Call Bullsh!t Till I Can Be Proven Wrong. I'd Love To See It Happen, But I'm Not Sure It's Possible Even With A Cummings Turbo Diesel & A 6 Speed. John

Oh, its possible..................With a Cummins

Only problem, It seems I get only 2 trannys and 3 driveshafts to a tank

Actually, it is down right unbelieveable............mpg wise. Having been driving/wrenchings on OTR trucks for years now, I am a firm believer the A$$ in the seat has alot to do with fuel mileage. I've seen two different guys run the same run, same truck, grossing the same amount of weight..........One guy gets 5 mpg, the other gets 7. Why? The guy getting 5 runs it like a 2 stroke Detroit to run at the posted speed limit..........Hammer down, and its just screaming+ he shifts lazy. The other guy uses the gearbox to run the engine, he climbs the gears and doesn't take all day doing it.........And he doesn't have to run the engine up in rpms and then let it fall again to shift it smooth because he knows what he's doing. Knows what he's doing..............Yup, Operators can make or break you when it comes to fuel mileage.

Mileage in these trucks can be had, but you ain't gonna burn Petrol doing it............Its all in an Oil Burner

[jooooooe]

My green '69 pick-up has (had) a 250/6 with a 3 speed, it got about 10-12 mpg which I think the 3:73 rear end had alot to do with it's poor mileage. At 55mph the truck sounded like it was tapped out, although you could stick it to the floor and it would still make 95mph top end, which is something I've never seen a 250/6 do, usually 80 mph is about all you can get outta' one. I think it might have made 15-16mpg with an OD trans. I would be happy with that. If I continue to have trouble finding stuff for this stupid 305, the 250 may find itself back in there with that new 200R4, the curiousity of it all is kinda' tempting.

[69TowRig]

Well, my poorly-tuned, dying 307 gets about 7 mpg in my K5. The good news is that my new Hemi Dodge is breaking in well, I almost pulled 15 mpg on it's 4th full tank (2500 QC LB).

I think everyone else is right, the aerodymanics of these vehicles just simply are not in line with getting decent fuel mileage. Maybe getting one of those under-bumper deflectors off the later generation trucks will help? A lighter right foot, correct tire pressure, ditch all the crap outta the bed, etc.

[nate68]

i saw something on tv the other day about Smokey Yunick. he devised some kind of weird intake thing with brushes or something and got 55mpg out of a Fiero.
i did a little research and it's called a hot vapor cycle engine. i dont get how it works and there's some kind of secret to it that apparently him and one other person know.

[jooooooe]

did he have a dog named Duke also?

[Longhorn Man]

1/2 of what you read or hear about Smokey is BS. If he had a Fiero getting 55 MPG... it woulda been headline news, even in the 80's.

[Fred T]

To get better milage out of one of these trucks you need the following:

Better gears. 3.07 is a starting point. Or ad od tranny to get there.
HEI dizzy, with the correct advance curve, total advance of 32* approx.
Q-jet carb, tuned for milage. One without leaky throttle shafts.
An egg placed on the accelerator.
High compression heads with a mild cam.

[67chevy2wd]

Originally Posted by Fred T

To get better milage out of one of these trucks you need the following:

Better gears. 3.07 is a starting point. Or ad od tranny to get there.
HEI dizzy, with the correct advance curve, total advance of 32* approx.
Q-jet carb, tuned for milage. One without leaky throttle shafts.
An egg placed on the accelerator.
High compression heads with a mild cam.

I am not disagreeing with you but how would high compression heads and a mild cam help gas milage. I might be a stupid question but I asked anyway

[blazerboy72]

IN my 72 im doing good to get 8-10, but it is lifted 8". Im hoping the LS1 will help the gas mileage in my 71 2WD.

[Huck]

My 72 LWB got 13, upgraded to a 96' truck 5 speed, edlebrock carb and HEI and got 18-21 highway. 307 rear.
Then put on hooker headers, lost 2mpg. then put in an edelbrock intake and lost another 1-2mpg. Went back to stock intake with edelbrock carb and regained that 1-2mpg. This was with a new GM crate 350 and running at or below 70mpg.
Now for comparison, my 97 Vette 6speed would give me up to 31-2 mpg crusing at 70-75 cross country with reguar gas.
My 2000 Z71 extended truck with 373 gears will give me 20mpg highway but 13mpg if towing weight.
Factors that improve mpg, --fuel injection, Hei, overdrive trans, rear gears, matching intake & headers to cam shaft, carb, and probably most of all, speed verses wind resistance. Oh yea, drop a 10lb sledge hammer on your right foot will also probably increase your mileage!!hehehehe