Best way of improving MPG?

[eighteenninetytwo]

Seems like I'm getting about 8PMG right now. it seems to be running a bit rich so I will adjust the carburettors a bit and might eke another MPG or 2 out like that, but are there any obvious ways of going about this (short of a new transmission with overdrive) that I should consider. Is it possible to change front and rear diff ratios by changing internal components for instance?

[SilverMiner]

I have a large collection of old magazines covering the era of our trucks (late 72 to mid 84-ish) such as Four Wheeler, Pickup Van & 4WD, Four Wheel & Off Road, and even some of the oddballs. By far the most covered subject is fuel mileage, which is no surprise considering the oil crisis in 73 and then again in 79. Back in the day, 8 to 10mpg was about what they got from real world testing. And their fuel was better than ours today - it still had lead until the late 70's and obviously no ethanol. Another big advance during the time period was radial tires with better rolling resistance than the standard bias ply's of the day.

Jump ahead to the 21st Century, and we are all running radial tires, probably with no smog equipment attached after four decades of use, but having to buy inferior fuel with less energy per unit volume. In my opinion and past experience a well tuned V8 in one of our squarebody rigs should hit low end double digits for mpg with 10 being the bottom for a cruising trip. Low speed trips in the woods or around town will easily dip into the upper single digits with 8 being the worst I'd plan for or expect.

Modern improvements can be found with fuel injected LS engines and computer controlled transmissions, and fortunately enough those also come with performance gains, but the installation cost will never be offset by fuel savings in a reasonable amount of time.

[eighteenninetytwo]

Yeah - I have looked at the cost of a 7004R transmission and the savings on fuel - even if I got 50% more MPG - would never be offset. I guess tuning the carbs and actually inflating my tires properly would help the most

[mickeykreg]

I started doing alot better MPG after installing an Autometer Air/fuel ratio gauge. Became much easier to pass the IM test here too. Only thing is I switched to a carb that would let me tune easier. The Q-jet has never done me wrong, but I couldn't change jets and metering rods very easy. I chose the 625 street Demon with the re-jet kit. Took quite a few tweaks, but I'm getting a pretty consistent 15mpg now. Better power on the hills too. Obviously, over 8,000' is a different tune for that of sea level and takes a few minutes to make the change.
I was real close to going with an EFI throttle body, but using a tunable carb with a A/F gauge is the way to go IMO for one reason; so I can work on it if I need to. The only thing that prevented me from going with the Holley Sniper was that if it failed I was sending it to Holley for repair. That's not an option for me while on the side of the road somewhere. If a carb fails I can diagnose, fix it, and move along. Factory 4 speed, 35's, 3:73's.

[Edahall]

Drive slower. Lol! I just completed a 3000 mi trip and kept my speed around 60 mph (engine turning over at 1250 RPM) and averaged 29 mpg with the rig in my signature. Also had my tires pumped up to 80 psi.

[geezer#99]

Properly inflated tires helps.
As does hooking up a vacuum gauge you can read easily and driving at the highest vacuum.
And maximize your initial timing. As well as your vac advance.
And make your apt adjustable in the carb.

[buffydores]

Originally Posted by Edahall

Drive slower. Lol! I just completed a 3000 mi trip and kept my speed around 60 mph (engine turning over at 1250 RPM) and averaged 29 mpg with the rig in my signature. Also had my tires pumped up to 80 psi.

Yeah, but that's like cheating with the 12V. Braggart.

[lowrodderchev]

Best thing I did for improve gas mileage was a LS swap 7 gallons gas Visalia to Paso Robles

[72MARIO]

Ls swap would be the most worth while swap. Not only do you get better mpg but the driveablity is greatly improved.

[eighteenninetytwo]

Yah - but an LS swap costs how much??? For every thousand dollars I spend I could drive another 2280 miles at 8 mpg and @ $3.50 per gallon.

[lowrodderchev]

Around $2800 into my LS swap and I haven't had one regret yet power gas mileage starts on dime

[eighteenninetytwo]

hmmm - better than i thought, but is that doing it yourself - My problem is i dont have the tech skills OR facilities / capacity to deal with that - i would be paying probably $100 per hour (in CA) to get it done. that might be the killer.

[Bluestep]

1982, you didn't provide any information about your vehicle. So generically speaking you need to check to see what has been modified on your rig. Does it have all the vacuum hoses hooked up correctly, does it have an aftermarket carburetor(s) (which is most likely set up rich), is the timing set correctly, has the advance curve been optimized? Check and repair or adjust all of those things and then do what you can to make the vehicle roll easier. That would include taking extra weight out of the vehicle (tools, tire chains, etc.), make sure the tires are properly inflated and are not overly wide. Check the gear ratio of the rear axle and if it is low (numerically high) will have a huge effect on mileage. You can help the gear ratio with a change in tire size (if it is too low use as tall a tire as is practicable, and correct the speedometer)

If it still has the Quadrajet carburetor it can be tuned to be very efficient.

After all the tune up has been optimized your driving skills need to be optimized for fuel efficiency.

After all of that you will still not have a vehicle that was designed for fuel efficiency, but it will be a cheap to maintain, useful vehicle. Economy isn't about just fuel mileage.

[eighteenninetytwo]

Wow. That is a ton of really good information and ideas. I am a total beginner at this stuff, so need to research all of this detail on the vehicle and report back.

[Fishermen0105]

I like to keep things simple. Seems like it would take a lot of mpg improvement to makeup for a new engine. I didn't buy a k5 for good gas performance anyway. I'd stick with the original engine and tune the quadrajet. Easy to work on and keeps things simple when you go to autozone for parts. Just my two cents...

[LostMy65]

I searched mpg in the thread titles, and this appears to be the most recent thread. Though I have a 65, the info still applies.
The most common replies I see whenever this topic comes up is:

1. We need an Overdrive Transmission.
2. We need FI
3. Our truck's weight
4. Our truck's aren't aerodynamic.

But when I do a mpg cost comparison, I don't want to look at just the cost of fuel. I want to compare the overall cost of what it takes to own and use my vehicle.

My 2010 Honda CR-V averages in my typical day to day driving 24 mpg. But in the last 8 years it has lost around $15,000 in value. And, eventually I'll need to start putting money into it to keep it going.
I did some Google searches to see if there's anyone that has put some of these numbers out there for what it really costs to own a new car. But to just give me a little comfort in some rough figures, my 65 may cost me as much as a new car after the cost of gas, and typical upgrades and maintenance, but my 65 is worth quite a bit more than when I bought it.
I'm thinking if I can get 15mpg out of my 65, the total cost over 10 years isn't going to be much more than buying a newer car that gets me better mpg.

[LT7A]

Originally Posted by LostMy65

I searched mpg in the thread titles, and this appears to be the most recent thread. Though I have a 65, the info still applies.
The most common replies I see whenever this topic comes up is:

1. We need an Overdrive Transmission.
2. We need FI
3. Our truck's weight
4. Our truck's aren't aerodynamic.

But when I do a mpg cost comparison, I don't want to look at just the cost of fuel. I want to compare the overall cost of what it takes to own and use my vehicle.

My 2010 Honda CR-V averages in my typical day to day driving 24 mpg. But in the last 8 years it has lost around $15,000 in value. And, eventually I'll need to start putting money into it to keep it going.
I did some Google searches to see if there's anyone that has put some of these numbers out there for what it really costs to own a new car. But to just give me a little comfort in some rough figures, my 65 may cost me as much as a new car after the cost of gas, and typical upgrades and maintenance, but my 65 is worth quite a bit more than when I bought it.
I'm thinking if I can get 15mpg out of my 65, the total cost over 10 years isn't going to be much more than buying a newer car that gets me better mpg.

That's a great perspective on true cost picture. Well done.

[LT7A]

1892, do you know who Gregski is on here? He has a great thread on using an air/fuel ratio gauge to tune your carburetor. Before I read his thread, I thought of those as a little bit gimmicky on a non fuel injected car. The performance and mileage benefits he's gotten from tuning are more than surprising. Actually nearly astounding. Searching other forums for mileage, MPG, hypermiling will give you a few ideas. Some people are open minded enough to understand that we want the best performance and mileage out of whatever we drive. Not just from a subcompact or a hybrid. If If I recall correctly, you have a lifted Blazer. I'm not going to suggest that you lower it, but the weight of the wheels and tires and the distance of the body above the ground have a big effect on mileage. Incremental improvements on those will show incremental gains. You can hunt down an air deflector to go under your front bumper. I like to get weather stripping and put it in the panel gaps on the front of my vehicles. Doesn't cost much, keeps the air from getting caught there, and cuts down a little on wind noise.

[Zoomad75]

Just to throw a monkey wrench into the equation... My lifted K5 with a 5.3/700r4 combo rolling on 35" tires and 4.10 gearing with a camper on it average's 13mpg. I've seen 1 tank as high as 16, but the overall tank to tank average is around 13 and change. Without the aero drag of the camper I was consistently getting close to 18 on the highway if I kept my foot out of it.

You can't overcome the physics for sure, but actually this is where power can help. The typical smog era 305's and 350's barely eeked out maybe 150-180Hp on a good day back when they were new. Challenge that weakness with age, wear, lift kits and bigger tires without regearing and you are asking for single digit MPG's. My old 75 was just that, 350, q-jet, 4-speed (non-od) manual, 3.73 gears with a 4" lift and 35's. On a good day I'd get lucky and squeeze 10mpg, but I either needed a fat tailwind or run downhill to get it. Most of the time it was 7-8 mpg, with 4-5 mpg happening off road/low range running. The 35's did lend a little OD effect as the size negated the 3.73's to act like a set of 3.42's. So sure my highway rpm went down at 60, but getting up to 60 took a while and a right foot planted on the floor. It offset any savings I was getting at highway speed.

There is no doubt that LS swaps are expensive if you aren't doing the majority of the work yourself. But the modern tech, combined with an OD transmission can work wonders. My little 5.3 has almost double to factory rated HP of the old 350's (before my aftermarket control system came in and gives a little more) and it's that HP and increased torque that gets my fat rig up to speed easier with the OD cutting the rev's down to barely 2000 rpm at 65. Prior to loading the camper on the 5.3 had enough beans to spin those 35's too. Now I got too much traction (weight) to even try. But none the less it's operating so much more efficiently than the best carb of any kind tuned in as best as it can be can do. One other note about serviceability with the LS I'm not stuck going back to Holley or one of the other aftermarket EFI companies if something breaks. Outside of my control system everything is stock GM for a 2002 Silverado 1500. I can walk into any part store in the country and get what I need for it. That being said I've put close to 13,000 miles on my swap so far and outside of a fuel pump issue, I've yet to have any problems.

There is always the 12v Cummins route if you are handy with a welder and like your rig sounding like a Kenworth. Not having done one myself, I'd bet the cost of that swap makes the LS swap look cheap too.

Outside of buying a set of LS swap engine mount brackets (there are a ton of sources now), there is no real fabrication required to do it. Really comes down to electrical and fuel plumbing. Get the right harness kit and the wiring is simple down to a few connections.

If the LS is still beyond reach mechanically or financially, the new wave of self tuning 4bbl TBI EFI systems are the next option. The price is coming down rapidly with competition from many vendors. You still run your small block so no new/used engine costs involved. Most of the kits are comprehensive having most if not all of what is needed to get running. Still to get the most out of it, OD is still a requirement.

There is a lot of ways to skin the cat in this case, but without EFI and OD in these trucks you are going to be stuck to single digit economy.

[rpmerf]

My view on MPG for just about anything -
Start with a good tune up. Make sure your carb is in tune. I got an A/F gauge on mine. Stoich-ish at idle, lean when cruising, nice and rich when I get on it.
Get some new plugs in there, maybe do wires, cap, rotor, coil, just so you know it is all good. Check your ignition timing. The topic of manifold vacuum advance or ported vacuum advance is debated, but I think the manifold advance really helped in the low end / high vacuum.

Reduce load. Remove unnecessary weight. A fan can kill 20+ hp. An electric fan steals a lot less power from the engine. If your fan is direct drive, a clutch fan reduces the load a bit, as the clutch fan only spins 80% of the crank speed and is very loose when the radiator is cool. If you have AC, that always kills power.

Reduce RPM. Your engine pulls fuel in every revolution. Fewer revolutions = less fuel. An overdrive transmission would be the best upgrade possible here. You might be able to play with your gear ratios, but then it is a balance of acceleration and gas mileage.