gas mileage - The 1947 - Present Chevrolet & GMC Truck Message Board Network

carolinajohndeere · 03-26-2016, 07:26 PM

Hi: I just bought a 1972 C50 with a grain dump bed. The brake lines were shot along with some wheel cylinders. Just got all that fixed and started driving the truck. It has a 350 engine, a 4 spped trans., and a 2 speed rear end. The rear end is a 6.50 ratio in hi range.

Anyhow, the truck runs great. The only problem is that it is getting reall bad mileage, less the 5 mpg. I know this is a low geared rear end, but a 6.50 was in a lot of the Chevy trucks.

What has been you experience with gas mileage on one of these. Once I know what I should be getting, I will start digging into the fuel system if needed.
Thanks in advance for your help.

South Florida C50 · 03-26-2016, 08:30 PM

It's never gonna be great, but you can make it better doing a few things that I did to my 1969. I had the same setup as you before I turned it in to a pickup. Try to keep up on the routine maintenance, new plugs, new wires, better air filter,change your distributor to an HEI, if your still using points. And the number 1 thing I did that really helped was upgrade to a high-flow exhaust system! It has to breath better to be more efficient. Night and day difference in the mileage.

C10 - C90 Bill · 03-26-2016, 10:43 PM

Great advice on the Exhaust.

It will sound a whole lot better too, lol.

Also as mentioned, give the engine a good "Super Tune".

I had both, a Flow-thru Exhaust and a Super Tune on a lot of my Chevys and I would get some great mileage out of them.

Also important is "how" you drive it.

jumpsoffrock · 04-03-2016, 06:00 PM

Once I swapped my rear gears from the 6.5:1 to the 4.86:1, I ended up driving it about 70 miles north to pick up a car. Topped off the gas in town, and as soon as I exited freeway again. Doing a rough calc, I got 10mpg. I was very satisfied with that.

I haven't even done a tune up on it! In 25 years! Still running the same plugs, wires, and points that have been sitting on it since my dad was given it in ~1989.

Tare weight is ~8400lbs., 327ci with 2bl rochester, 4-spd, 2-spd rear

P.S. I have new plugs etc, a junkard HEI, the need for a new exhaust, and finally changing to an electric cooling fan coming down the pipes though.

I really can't wait to see what mileage it gets after that.

03-26-2016, 07:26 PM	#1
carolinajohndeere Registered User Join Date: Mar 2016 Location: Davidson Posts: 1	gas mileage Hi: I just bought a 1972 C50 with a grain dump bed. The brake lines were shot along with some wheel cylinders. Just got all that fixed and started driving the truck. It has a 350 engine, a 4 spped trans., and a 2 speed rear end. The rear end is a 6.50 ratio in hi range. Anyhow, the truck runs great. The only problem is that it is getting reall bad mileage, less the 5 mpg. I know this is a low geared rear end, but a 6.50 was in a lot of the Chevy trucks. What has been you experience with gas mileage on one of these. Once I know what I should be getting, I will start digging into the fuel system if needed. Thanks in advance for your help.

03-26-2016, 08:30 PM	#2
South Florida C50 Registered User Join Date: Oct 2014 Location: Fort Lauderdale, Fl. Posts: 53	Re: gas mileage It's never gonna be great, but you can make it better doing a few things that I did to my 1969. I had the same setup as you before I turned it in to a pickup. Try to keep up on the routine maintenance, new plugs, new wires, better air filter,change your distributor to an HEI, if your still using points. And the number 1 thing I did that really helped was upgrade to a high-flow exhaust system! It has to breath better to be more efficient. Night and day difference in the mileage. Attached Images

03-26-2016, 10:43 PM	#3
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,067	Re: gas mileage Great advice on the Exhaust. It will sound a whole lot better too, lol. Also as mentioned, give the engine a good "Super Tune". I had both, a Flow-thru Exhaust and a Super Tune on a lot of my Chevys and I would get some great mileage out of them. Also important is "how" you drive it. __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

04-03-2016, 06:00 PM	#4
jumpsoffrock Registered User Join Date: Apr 2014 Location: California Posts: 925	Re: gas mileage Once I swapped my rear gears from the 6.5:1 to the 4.86:1, I ended up driving it about 70 miles north to pick up a car. Topped off the gas in town, and as soon as I exited freeway again. Doing a rough calc, I got 10mpg. I was very satisfied with that. I haven't even done a tune up on it! In 25 years! Still running the same plugs, wires, and points that have been sitting on it since my dad was given it in ~1989. Tare weight is ~8400lbs., 327ci with 2bl rochester, 4-spd, 2-spd rear P.S. I have new plugs etc, a junkard HEI, the need for a new exhaust, and finally changing to an electric cooling fan coming down the pipes though. I really can't wait to see what mileage it gets after that.



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