Need to improve mileage!

[extd56]

I only get 15MPG in my Avalanche and that is with overdrive and fuel injection. I am getting about 18 with my 67 extended cab truck with a 91 TBI motor and a 400 trans with 3.07 rear gears.

[Average Joe]

16.5 mpg or thereabouts was the best mileage I ever got with my 69 C10 when I had a 250 6 cyl. in it wth 3.73's. This was cruising at 60 mph on flat interstate. I have heard of some guys on here approaching 18mpg highway with a 250 and overdrive in a 2wd. As far as the original poster's question I would suggest a Q-jet carb for the best fuel economy if not already running one. I went fom a quadrajet to a carter 625 on my old Chevelle and lost 2 mpg. You might also consider a narrower tire. I'm assuming your 32's are 11.5 wide. BFG as well as others make a 33/9.5/15. May be something to consider if your in the market for tires any time soon. I've heard synthetic oils in all diffs and gearboxes help as well, though I wonder how much.

[OhOneWS6]

Originally Posted by extd56

I only get 15MPG in my Avalanche and that is with overdrive and fuel injection. I am getting about 18 with my 67 extended cab truck with a 91 TBI motor and a 400 trans with 3.07 rear gears.

What year Av? I only get 14 out of my 07 Avalanche. I got 16 MPG out of my 04 Avalanche. The 72 only gets 12.

[unclewatts]

Originally Posted by gmc1971harwich

hey how about all u 6 cyl owners. what are you getting for gas mileage? that might be a way to go, combined with a 700r4 trans i would think that combo would give you the best mileage possible for your truck, wont go as fast but should be pretty economical.

I have a friend with a 70 C-10 shortbed stepside with a 250 6 and manual three on the tree. The truck has stock diameter tires. He figured his best highway mileage was about 15 MPG with a Rochester 2 barrel carb. I got a 70 longbed stepside with a 350, manual 4 speed floor shifter 4 barrel Rochester carb, headers, 3:08 posi rear end and 32" tires and I figured out that the best that I get is about 14 MPG. I think the moral of this story is when you have a heavy truck with a lousy coefficient of drag (in other words a Barn Door) it takes so much energy to move it no matter what engine/induction system/rear end ratio you have you're gonna suck a bunch of gas.

[capev86]

no big blocks
2wd is better on mileage than 4wd (saves weight, less moving parts)
softer gearing (no 4.56's)
overdrive - 700r4, 5 or 6 speed etc.

i bought my 72 burb because it 2wd because i love the looks and ride of the all coil suspension on these trucks. i won't be doing much winter driving and burbs have better traction than pickups anyway. my truck wieighs a bit more because it is a 3/4 ton but probably still less than a 1/2 ton 4x4 because most of the extra mass is in the springs, trailing arms, etc....not a big beefy front axle. it makes oil changes easier too. i am converting the ho52 from a 4.57 to a 4.10 gear which will get me a 10% drop in rpms. that means that the difference will be almost nill at a slow crawl, but the faster i go, the more rpm's i'm saving. i also want to add the factory overdrive to the saginaw 3 on the tree but the few of those out there are demanding very high prices.....$350 for a rebuildable core on ebay just recently.

[Lippyp]

I ran my truck as my daily for a couple of years but with gas prices the wya they are over here (at their peak around $8/US Gallon) it just wasn't practical. I now have a 98 Isuzu Trooper with a 3.1L turbo diesel that gets mid twenties and the wife has a Nissan X-Trail company vehicle that gets mid 30's.

[Critter]

Originally Posted by unclewatts

I think the moral of this story is when you have a heavy truck with a lousy coefficient of drag (in other words a Barn Door) it takes so much energy to move it no matter what engine/induction system/rear end ratio you have you're gonna suck a bunch of gas.

You hit the nail on the head.

[extd56]

Originally Posted by OhOneWS6

What year Av? I only get 14 out of my 07 Avalanche. I got 16 MPG out of my 04 Avalanche. The 72 only gets 12.

Its a 03 Avalanche

[C-10 simplex]

Here's a scrap of info that i just picked up that might be a cost-effective solution for your problem:

Try putting 305 heads on your 350; It will raise compression which equals better mileage and power. At least low-end power.

As you probably know, 305 heads can be gotten cheap if not free.

[69sixpackbee]

My '72 402/4-speed gets 10-13 around town and maybe eek out 15 on the hwy. Tried EFI--gained 1-2 MPG but still this truck is about as aerodynamic as a brick. Youre stuck with the mileage. But for the WOW factor it is worth it taking in the shorts at the pump. Folks love seeing my '72 with a big-ass Lance camper strapped to the ass-end..especially when I out perform the newer ones up a grade!
I would'nt change it. I have my "daily" driver for gas mileage. I use this truck for hauling stuff and summer vacations.

--Bud

[yote1234]

the way i see it is we all! stop at the station sooner or later.. so just buy a bigger tank...

[C-10 simplex]

The other thing that i wanted to touch upon, (but i don't have time to investigate whole-hog right now, but in the meantime consider these)was, let's see what we can do first to save on gas without even considering the truck. Without opening the hood, making modifications etc.

For example, i think Discover has a credit card that refunds 2% on all gas purchases.

i'm pretty sure shell and BP also have similar.

i think american express has one that refunds 4% on gasoline purchases. It has an annual fee though, so we need to take that into consideration. Probably still worth it.

Again, i don't have time to get into it whole-hog, but my strategy would be to try to first do anything/everything you can to save on gas, then maybe make modifications to the truck.

i think it has to do( i know it does for me) more about money than actual mpg; If gas were .35 cents a gallon, would anyone give a crap about mpg?

[haysonj]

I pay cash for my gas as at most places in Calif its 4 or 5 cents cheaper with cash

[C-10 simplex]

Yeah, that too---cash may be cheaper than credit card at some stations.

Also i think Speedway sold/sells gift cards worth $50 for $48 or something like that. So if you bought that using another credit card that pays % refund, then this could be a substantial savings.

There's a whole world of savings concerning gas that don't even involve the car. i do not, presently, have time to investigate this world.

[clay68c10]

I'd say go EFI, but the $ difference isn't that much when you do the math. I got 2mpg out of my TBI.
Now if you consider the cold start driveability, it's a whole new world.

[Myself]

How about Hydrogen On Demand? My neighbor bought a '97 Lexus 4X4. It's just like a Toyota Landcruiser. It has 170,000 on it, and a 4.3 24valve inline 6. He was averaging about 13.5 mpg everyday driving. I have always wanted to try the HHO systems but have been very skeptical. He called me up one day and told me he had a Hydrogen system coming, and asked if I'd hook it up. So, after a couple of evenings (about 6 hours) it was installed and operational. The toughest part was finding a place to mount the equipment under the hood of that thing. Anyway he now averages 16.5mpg for about a $400 investment.

[71longbed-brew]

the best i ever got with 3.07 ratio is 15.8 mpg on the freeway ... i haven't checked the mpg since the 3.42's went in ....

it amazes me that a carbed 40 year old truck get only afew mpg less then a computer controlled newer truck ... theres not much evolution there

[CCCC]

It's all been said in this thread - many practical suggestions for improved MPG and some good analysis of cost/benefit over time. A big factor seems to be psychological - that we rarely have to repair or modify our trucks, but we regularly have to go to the pump, so we get frequent reminders of our fuel cost and consumption. My reason for having all of these old Chevs/GMCs is that THEY WORK, they are fun and they look wonderful. The difference in MPG between the lightest and heaviest is minimal and that comes with this series truck. On some I can get 14 MPG which seems pretty good, but the C30 with 402BB and a HEAVY chassis mount motorhome camper will get 12 MPG if I take it easy, and we drive it all over the US. Of course it looks old fashioned and ugly to some (some of my kids live in rather fancy neighborhods, but I still park it in their driveways) and even though we could own a much bigger modern motorhome with all the fancy stuff - this is my choice because I like to drive it and it feels great. You might be surprised how many knowing smiles, compliments and offers to buy it on the spot I get every time we venture cross country. So, the higher fuel consumption is one of the costs of love and distinction. There are much higher costs being paid in life.

[Critter]

Originally Posted by CCCC

It's all been said in this thread - many practical suggestions for improved MPG and some good analysis of cost/benefit over time. A big factor seems to be psychological - that we rarely have to repair or modify our trucks, but we regularly have to go to the pump, so we get frequent reminders of our fuel cost and consumption. My reason for having all of these old Chevs/GMCs is that THEY WORK, they are fun and they look wonderful. The difference in MPG between the lightest and heaviest is minimal and that comes with this series truck. On some I can get 14 MPG which seems pretty good, but the C30 with 402BB and a HEAVY chassis mount motorhome camper will get 12 MPG if I take it easy, and we drive it all over the US. Of course it looks old fashioned and ugly to some (some of my kids live in rather fancy neighborhods, but I still park it in their driveways) and even though we could own a much bigger modern motorhome with all the fancy stuff - this is my choice because I like to drive it and it feels great. You might be surprised how many knowing smiles, compliments and offers to buy it on the spot I get every time we venture cross country. So, the higher fuel consumption is one of the costs of love and distinction. There are much higher costs being paid in life.

AMEN!

[evilways]

Originally Posted by special-K

...S--L--O--W--------D--O--W--N.......Seriously! It`s the most effective way to save fuel "and" money.

My 3/4t 4wd gets 12.5 mpg,what do you get?What type of driving do you mostly do?You can spend money on this or that or keep the money or gas.The best mileage gainer is a light right foot.I get best mileage at 60 mpg with 3.54s/12.50x33s/TH350/350.

No helpful info from me on this other than I completely agree with special-K. I don't have numbers but when it is dry and warm I would go a week on a tank back and forth to work in town, now it is cold and sometimes slick, so from take off I just barely set my foot on the pedal to go and I am off the pedal much sooner when the lights turn red, now I am getting almost two weeks to a tank and that is also after adding about 200lbs to the bed for winter weight. So for me with an extra 200lbs and a light foot I am saving close to $70 a month. I can live with that. Now hopefully I can keep it up when it warms up and my windows are down and I can hear my truck rumble.

[knsmodels]

Headers with a good flowing exhaust and electric fan (removing the stock one) would get you a little more mpg.....jmho

[Lippyp]

After the Copenhagen summit this might be a conversation more of you will have! Its already an issue over here with larger engined vehicles facing fairly hefty tax penalties both at purchase and annually with hybrids and small efficient cars getting various tax breaks. Many smaller cars here will now do in excess of 50mpg.

[mrein3]

Originally Posted by Lippyp

After the Copenhagen summit this might be a conversation more of you will have! Its already an issue over here with larger engined vehicles facing fairly hefty tax penalties both at purchase and annually with hybrids and small efficient cars getting various tax breaks. Many smaller cars here will now do in excess of 50mpg.

It is funny this subject is brought up at this time.
Assuming this alleged global warming is man made, why won't this far left wing government that is driving us daily towards all out socialism, allow the US automakers to build a car with a small, turbo charged deisel engine?

Everybody knows these smaller cars with turbos and direct injection and manual transmissions get 50+ mpg. Why won't our government and the executive branch push for such vehicles? We all know the answer but this isn't a political forum it is a car forum and this is a post about 50+ mpg cars, not soalistic left wing governments trying to control your life through higher fees and taxes.

[va72longhorn]

Back in the early eighties, a friend of mine bet me a case of beer that he could get my 2 wheel drive '72 blazer to get over 25 mpg. I was running a 305 with 296 valved heads, 4 barreled with headers.Thinking I had a free weekend of beer coming to me , I took him up on it. Not that I'm condoning this, but he pulled the blazer in his garage and pulled the 4 nuts and studs holding the carb down. Then he went over and after rummaging around, pulled out a piece of stainless steel door screen and cut a piece a little larger than the quadrajet. Next he sandwiched it between my carb gasket and another gasket he had hanging on the wall.
Long story shorten..... 29 mpg and more power! Seems the theory was that the gas hits the slightly heated screen and vaporizes. Gas vapors burn easier than gas liqiud. Supposely, someone came up with this theory back in the '60s and the oil companies bought the patented idea...... so he said. All I know is I was out a case of beer!

[Critter]

Originally Posted by va72longhorn

Back in the early eighties, a friend of mine bet me a case of beer that he could get my 2 wheel drive '72 blazer to get over 25 mpg. I was running a 305 with 296 valved heads, 4 barreled with headers.Thinking I had a free weekend of beer coming to me , I took him up on it. Not that I'm condoning this, but he pulled the blazer in his garage and pulled the 4 nuts and studs holding the carb down. Then he went over and after rummaging around, pulled out a piece of stainless steel door screen and cut a piece a little larger than the quadrajet. Next he sandwiched it between my carb gasket and another gasket he had hanging on the wall.
Long story shorten..... 29 mpg and more power! Seems the theory was that the gas hits the slightly heated screen and vaporizes. Gas vapors burn easier than gas liqiud. Supposely, someone came up with this theory back in the '60s and the oil companies bought the patented idea...... so he said. All I know is I was out a case of beer!

That's an awesome story! I think someone should submit it to Mythbusters so they can scientifically test it...and keep me entertained. We've all heard stories of things like this, I have always wanted to try a few and see what results I get.