Dont take this as ignorance but as gaining knowledge

[68longhorn]

my 86 swb with 305/700r4 and 2.73 gears got 17mpg on its last tank of city and highway driving.

[Dieselholic92]

I guess if I was building a truck just for fuel economy, I would do electric fans, a ram air intake from Spectre, electric water pump, 700r4, 3.08 or 2.73 rear, headers, dual exhaust, synthetic oils, HEI distributor, better spark plugs, some sort of fuel injection, and probably lower it. I'd make sure the motor has good compression too.

[Axle]

Originally Posted by LeatherMan69

Now I want to know all the tricks of the trade to squeezing all the MPG's i can out of this beast of a truck. I did the math and currently getting 8.8mpg. Like i said IM NOT IGNORANT I KNOW THESE TRUCKS ARE GUZZLERS! So just know that. But im a firm believer that just cause its not a drastic change doesnt mean it shouldnt be done.

Just a little side note with regards to fuel mileage, ethanol poisoned fuels practically kill any fuel mileage you may have had otherwise. My truck (back when we still had a choice) would see anywhere from a 50-75 mile REDUCTION in range before needing to refill again anytime I ran an ethanol (10%) fuel. Just something to keep in mind when you find you are not obtaining mpg numbers that used to be considered normal for our trucks.

Alex.

[kylep]

Originally Posted by GMC Guy

nobody's mentioned an overdrive trans?
i get about 10 in town and 12 highway with the combo in my sig. But i can't wait to get my 700r4 and 3.73's installed. should be getting around 17-20....with a light foot......we'll see if that happens

i have a 400 tranny and my truck drives great, i am thinking about getting the 700, because i live in san diego so all my driving in freeway for at least an hour to get out of town,. will a 700 really improve my mileage?

i got a 468 engine and she dont drink she gulps!

[gchemist]

Use modern technology.
ZZ4 355+HP motor with aluminum heads.


13-15 MPG city (semi-lead foot)
18.5 MPG highway @70 MPH. I bet it could hit 20 if I slowed down.

[Goldfinger]

Mine is a 305/700r4 2.73 gears. I rebuilt my carb and leaned it out a little. I've completely changed my driving style. low back pressure pipes. solid smooth acceleration to speed. use engine braking to plan stops. If you keep off the brakes it will do wonders for your wallet. I went on a 1400 mile round trip and averaged 26mpg mostly going 75-80. however around town i get 16 or less. highway towing with a heavy travel trailer 14-15mpg. The a/c compressor in my truck will burn almost twice as much fuel; feels like i'm towing a load when i turn it on.

[big10ratrod77]

Originally Posted by Axle

Just a little side note with regards to fuel mileage, ethanol poisoned fuels practically kill any fuel mileage you may have had otherwise. My truck (back when we still had a choice) would see anywhere from a 50-75 mile REDUCTION in range before needing to refill again anytime I ran an ethanol (10%) fuel. Just something to keep in mind when you find you are not obtaining mpg numbers that used to be considered normal for our trucks.

Alex.

With my calculations if my 77 big ten had a 50-75 mile drop in range i would be getting 15 gallons to the mile

Well the biggest part of fuel econ is how you drive no jack rabbit starts and no poking off the line drive with sense.

A few other things I would try is a block heater, I am the kind of person I hate to race a cold engine its the way my dad raised me so I let mine warm up for at least five minutes before I leave the house and that really hurts mileage, but if you install a bock heater in your truck and have it on a timer where it cuts on at like 3 hours before you leave for work, school or where ever. Also with a block heater your engine can run more efficiently sooner.

Next would be an electric fan but they are a little pricy and wiring up a relay has always confused me. If you have a clutch fan check and make sure it’s not locked up, and if it is replace it.

Engine tune is also very important. My 77 you mash the gas once and touch the key and it is running no extra fuel wasted in the starting process. when my dad gave me the 77 in my sophomore year of high school it was in poor sate of tune I was getting about maybe 8 at the most, I added true duels with turbo mufflers and adjusted the carb set the timing replaced plugs, wires, cap and rotor, pcv valve the little breather for the pcv valve, new k&n air filter and it was capable of like 12 mpg but now it ran really good and I kept my foot in it a lot.

one more gear syndrome, we have 3 trucks that suffer from "this truck feels like it needs one more gear" at the Huskey house hold my k10 and dually have 4.11's and my big ten has 3.73 gears all three trucks will pull like a hoss but fuel econ suffers when I restore my 77 big ten I plan to add an overdrive unit in front of the stock granny gear to get my rpms down on the highway. so if you can get your rpms lower it can help your mileage you kind of want a good balance of low rpm and torque in your cruzing rpm range

engine rebuild, there is no doubt in my mind that a rebuilt motor will get better mileage than one with 200,000 miles, my current project is a 79 Chevy with a 250 3ott and 3.08s in the back and its good for about 16 mpg on the highway but the engine is warn out so I found a non integral 250 we put slightly larger valves with a 3 angle valve grind and had .040 milled off the head so we have an improvement in air flow through the head and a little more compression, as for the block it will stay all stock except for a slightly larger cam. Everything we have put into this engine is to make it more efficient is if you do decide to overhaul your engine keep it fairly stock for best mileage results

Power steering is not designed to eat up much more than about ½ of a horse power but if your die hard set on getting another mpg you can always put manual steering on it

Tall skinny tires like mentioned before can help mpg, avoid low rolling resistance tires because they can cause you to have longer stopping distances and that’s not safe

[Edahall]

Originally Posted by Goldfinger

Mine is a 305/700r4 2.73 gears. I rebuilt my carb and leaned it out a little. I've completely changed my driving style. low back pressure pipes. solid smooth acceleration to speed. use engine braking to plan stops. If you keep off the brakes it will do wonders for your wallet. I went on a 1400 mile round trip and averaged 26mpg mostly going 75-80. however around town i get 16 or less. highway towing with a heavy travel trailer 14-15mpg. The a/c compressor in my truck will burn almost twice as much fuel; feels like i'm towing a load when i turn it on.

Wow, 26 mpg at 75-80 mph is even better than I can get with my 1982 Suburban with it's 6.2 L diesel (3.08's / 700R4) / 2x4). I can barely squeeze 30 mpg at 55 mph but going 75 mph, fuel economy plunges to 24 mpg. If you're getting 26 mpg at 80 mph, I bet it would get way over 30 mpg at 55 mph. Try it some time.

Can you list the modifications done to help increase fuel economy? Did you lower your truck? Any aerodynamic mods? I know that kind of amazing fuel economy took some work to obtain.

[Dalaigh]

Originally Posted by Edahall

Wow, 26 mpg at 75-80 mph is even better than I can get with my 1982 Suburban with it's 6.2 L diesel. I can get 30 mpg at 55 mph but going 75 mph, fuel economy plunges to 24 mpg. If you're getting 26 mpg at 80 mph, I bet it would get way over 30 mpg at 55 mph. Try it some time.

Can you list the modifications done to help increase fuel economy? Did you lower your truck? Any aerodynamic mods? I know that kind of amazing fuel economy took some work to obtain.

The biggest thing helping his truck is the 700r4 and the 2.73 gears. Your 6.2 probably runs a th400 and 3.73's? But you can still tow. With his set up he can tow, but not well. In fact, I'd recommend against it. And not because of the 700r4, like most would think. With the 2.73 gears, he wouldn't be able to get out of his own way, great fuel economy but no grunt. With those gears he probably gets better fuel economy at 75 then he would at 55, because they are designed for higher speeds

[Corts60]

Honestly, overdrive I think is the answer here. I have 3:73's but when I am in overdrive (Gear Vendors), my final drive ratio is 2:91. This is the best of both worlds because you still have low end grunt to tow and get off the line, but on the highway, you can relax the RPM's and sip the fuel.

However, I realize the cost of GV these days would take forever to pay back in mileage gained. You could buy a cheap Toyota Corolla that gets 35 MPG for less than you could buy a GV.

[Dieselholic92]

Originally Posted by kylep

i have a 400 tranny and my truck drives great, i am thinking about getting the 700, because i live in san diego so all my driving in freeway for at least an hour to get out of town,. will a 700 really improve my mileage?

i got a 468 engine and she dont drink she gulps!

A 700r4 should improve your mileage somewhat since it's a 3 speed with overdrive versus the 3 speed TH400

[nekkidhillbilly]

700 is a four speed 4th gear is od
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[Dieselholic92]

I worded that weird, but I meant it that the 700r4 is essentially the same as a th400, but it has an overdrive (4th gear)

[Goldfinger]

Luckily the 700r4's low 1st helps me get moving. If i wanna push it i can hit 0-60 in around 9 seconds, But doing "ANY" of that brings it way down. Before i rebuilt my carburetor it was getting 8.

[Edahall]

Originally Posted by Dalaigh

The biggest thing helping his truck is the 700r4 and the 2.73 gears. Your 6.2 probably runs a th400 and 3.73's? But you can still tow. With his set up he can tow, but not well. In fact, I'd recommend against it. And not because of the 700r4, like most would think. With the 2.73 gears, he wouldn't be able to get out of his own way, great fuel economy but no grunt. With those gears he probably gets better fuel economy at 75 then he would at 55, because they are designed for higher speeds

I've got 3.08 gears and tall and skinny tires. However, I think it takes a lot more than just tall gears to get 26 mpg at 80 mph. At that speed, our square bodied trucks push a tremendous amount of air so it requires a lot of power to maintain that speed. And also, the most fuel efficient full size trucks out there such as the Ford Ecoboost 3.5L V6 doesn't come close to getting 26 mpg especially at 80 mph.

[Keith Seymore]

Originally Posted by Dalaigh

Is the truck 2wd? If so look into lowering it, I don't mean slamming it to the ground, but if you lower it say 2/4 or 4/6 just enough to get less air moving under the truck (where theres the most friction) you should get some MPG out of that. Oh, and if your truck doesn't have a lower bumper valance, get one. It's designed to keep as much air out from under the truck as possible.

x2

The frontal area is the "projection" from the top of the truck all the way to the ground (like the hole it would make if you ran it through a wall).

Dropping the truck down reduces the front area, which is a term that is squared in the coefficient of drag equation.

K

[Keith Seymore]

BTW - my '87 is a 4.3L V6, 3.73 axle with a .73 overdrive, P235 tires - gets between 20 and 22 mpg most days (70 mph).

K

[Edahall]

Originally Posted by Keith Seymore

x2

The frontal area is the "projection" from the top of the truck all the way to the ground (like the hole it would make if you ran it through a wall).

Dropping the truck down reduces the front area, which is a term that is squared in the coefficient of drag equation.

K

From what I've seen, lowering the truck is about the best modification for increasing fuel economy on these trucks.

On my 1982 Suburban (6.2L diesel, 3.08 gears, stock heigth), it only gets 24 mpg at 70 mph. If I reduce the speed down to 55 mph, I have seen fuel economy as high as 30 mpg. I'm sure that if I slammed it, high speeds would not make such a difference.

[INSIDIOUS '86]

Alright I'd I was going to fry an egg with a magnifying glass here's how I would do it

The trucks are basicly going Down the road like the broadside of a barn.
1.lower it as far as you can.
2. Get rid of the weight. No sway bars no tail gate
3. Tonnue covers may or may not help. What does is a tailgate net
4. A/c looks great in the recycle bin.- less weight
5. We have grandma steering. Get rid of the power steering. Been driving this way for three years steering effort isn't bad an you finally get feedback
6. Kill all emissions equipment
7. Electric fans don't kill hp
8. Aluminum bumper brackets
9. Fiberglass hood
10. No sound deadner
11. 305 with a tpi and 700r4 2.73 gear or 3.08
12. No dumbo mirrors
13. Shortbeds are better on gas
14. Low rolling resistance tires
15. Sport rear bumper is lighter than a step bumper.
Roll pan is better still. Including front roll pan
16. Aluminum engine components like water pump, heads, intake, and a mini starter all kill weight in a big way

These are things that are attainable by the majority of all square owners
You can go with a new Lsx swap and make more power with as much fuel being burned
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[big10ratrod77]

http://usbodysource.com/

this place has complete fiberglass bodys for 73-87 chevys they also sell beds, fenders, cabs and everthing else...

you just are going to need money as long as train smoke and alot of time to get everything to fit right but that would realy cut down on your weight