How can I improve fuel economy?

[highwinger]

I know, I know, it seems futile, but from what I've read around here, I think it should be better than what it is. My last fill up was 20g/200mi...easy math 10mpg. It has been 11 recently. Shouldn't it be closer to 14mpg?

I don't know many specifics about the engine. Supposed to be a 350 crate only 7k miles on it. Some of what I know it has: double-hump heads (not sure which size), 1406 edel carb & intake, normal exhaust manifolds, flowmaster mufflers tho. TH400, 2WD 3.42 posi rear, 20x9.5" AL wheels, 30" tires. No third seat. MSD dist & CDU (no vac tho). PS PB rear AC

From what I've read:
- the double-humps are more suited for a 2 bbl -$500
- Q-jet better
- larger wheels are heavy & reduce eco - $2k
- overdrive & EFI would be no brainers - $3k ea
- pulleys not quite aligned might cause drag
- driving style is a factor

Any other suggestions on what I can check/improve? What's the best bang/buck mod? Cam? Heads?

Appreciate the help

[bigrigpardo]

overdrive trans like a 700r4 4l60 or 4l80 those would be best bet and cheapest depending on if you score a deal on used parts

[vectorit]

Any direction you take going forward will cost a good chunk of money I am sure.

Just my take on this subject in short.

O/D transmissions will always help
Gearing in the axle.
Add on O/D - Gear vendors device
Fuel injection is more efficient
Better cylinder heads - Those old double hump heads tend to have big intake valves. Aside from removing them to verify, you can look up the casting number found inside in between the rocker arms.
Ignition timing - Not sure why your vac advance is not there?
Tire pressure
Clutch fan
belt driven accessories like AC can add stress
Brakes, make sure they are adjusted so that none are dragging.

All in all, the Suburban is a big heavy barn of a truck moving down the road. Even the new Suburbans with all the latest technology gets pretty low MPG.

[Kevin McPherson]

try a stock Quadrejet carb, I have ran several edelbrocks, I have never gotten more than 10 or 11mpg out of them. I had a 72 chevywith a 350 ,worn out Qjet, someone suggested an edelbrock so I tried it, instantly cut mpgs in half went from 16 to 8. rebuild the quadra jet and wound up with 18mpg average
maybe someone can tune them but I can not.

[highwinger]

Originally Posted by Kevin McPherson

try a stock Quadrejet carb, I have ran several edelbrocks, I have never gotten more than 10 or 11mpg out of them. I had a 72 chevywith a 350 ,worn out Qjet, someone suggested an edelbrock so I tried it, instantly cut mpgs in half went from 16 to 8. rebuild the quadra jet and wound up with 18mpg average
maybe someone can tune them but I can not.

Wow, with what tranny & rear?

[3drburb]

Originally Posted by Kevin McPherson

try a stock Quadrejet carb, I have ran several edelbrocks, I have never gotten more than 10 or 11mpg out of them. I had a 72 chevywith a 350 ,worn out Qjet, someone suggested an edelbrock so I tried it, instantly cut mpgs in half went from 16 to 8. rebuild the quadra jet and wound up with 18mpg average
maybe someone can tune them but I can not.

Please give some more information on your setup. 18mpg average or even close would be great.

[dougo]

I've been researching, talking with local classic car/truck guys about going fuel injection. Kits can range in price but many have said I'd increase MPG by 5.

Seems quite a jump... Hard to believe. Still researching....

[Johnnyhotrod]

Double hump = camel back no? 63cc chamber? used to be the poor mans hot rod heads after machining for 202 intakes. Wouldn't think this is the problem. But not an expert...

Found this in an add for a distrib... "Adjustable vacuum advance canister to improve economy."

[Bigdav160]

Those old cylinder heads are fine. State of the art in their day.

Is the 10 mpg average? I'm not sure there is a lot of room for improvement. I've driven Suburbans most of my life. I put 250,000 miles on a '93 4x4. 13 mpg city and 16 highway was all it ever did. This is with fuel injection, overdrive, and better aerodynamics. We drove a new Escalade on a 2500 mile trip recently. 18 mpg in the highway is all we could get with my feather foot. A buddy of mine just bought a new ford truck with the turbo V6. He's crying about 12mpg but I tell him it's physics. It's going to take a certain amount of energy to move that mass down the road.

What type of ignition do you have? Make sure the advance units are working properly and giving enough spark advance. A Q-jet might give you an extra 1 mpg but don't expect magic.

[highwinger]

Originally Posted by Bigdav160

Those old cylinder heads are fine. State of the art in their day.

Is the 10 mpg average? I'm not sure there is a lot of room for improvement. I've driven Suburbans most of my life. I put 250,000 miles on a '93 4x4. 13 mpg city and 16 highway was all it ever did. This is with fuel injection, overdrive, and better aerodynamics. We drove a new Escalade on a 2500 mile trip recently. 18 mpg in the highway is all we could get with my feather foot. A buddy of mine just bought a new ford truck with the turbo V6. He's crying about 12mpg but I tell him it's physics. It's going to take a certain amount of energy to move that mass down the road.

What type of ignition do you have? Make sure the advance units are working properly and giving enough spark advance. A Q-jet might give you an extra 1 mpg but don't expect magic.

I haven't had the burb very long. That was the average of my last fill up...200miles/20gal. I've seen 11.2mpg. I've had my foot in it lately. I was getting a low power (take off) hesitation, so I've been playing with the carb tuning (rod, spring & pump lever). I also got the AC working, so I've used it more. It's a mix of hwy & city miles.

Been planning on taking it to NC, but 10mpg is making me rethink it. I do have an '04 Dakota with a 4.7L EFI OD that gets just under 17mpg on the hwy. The diff would pay almost pay for my last BrothersTrucks order

[theastronaut]

No need to go to fuel injection, just tune your carb. Get an Innovate wideband air/fuel ratio gauge to see how rich it is running, then re-jet accordingly. The timing will need to compliment the jetting too. You can lean out the accelerator pump amount until it starts to stumble, then go back up slightly.

I have a '64 VW bug that used to get 23-24 highway mpg with the stock single barrel carb. I swapped to dual Dellorto two barrels and it's gotten as high as 36.25 on the highway. It's never got lower than 28.5 city mileage since swapping and that's driving it hard. Carbs can get great mileage, they just have to be tuned.

[highwinger]

One side note is the previous owner said he got 18-19mpg with this burb. I didn't take it too seriously with my Camaro, Dakota & Conversion Van experience. On the ride home, I found the speedo read 85mph while doing 75 actual which also overstated the miles with incorrect settings on the Digital Dakota Dash. I've since adjusted the speedo & tach.

[highwinger]

Originally Posted by theastronaut

No need to go to fuel injection, just tune your carb. Get an Innovate wideband air/fuel ratio gauge to see how rich it is running, then re-jet accordingly. The timing will need to compliment the jetting too. You can lean out the accelerator pump amount until it starts to stumble, then go back up slightly.

I have a '64 VW bug that used to get 23-24 highway mpg with the stock single barrel carb. I swapped to dual Dellorto two barrels and it's gotten as high as 36.25 on the highway. It's never got lower than 28.5 city mileage since swapping and that's driving it hard. Carbs can get great mileage, they just have to be tuned.

Looks like some valueable info on that site: http://www.innovatemotorsports.com/r...FI_mileage.php

snippit:

Old School Meets New School :How to Get EFI-Quality Mileage From Your Carburetor (By Stanford Curry)

Think you can't have a small-block that lays down 556 hp, 512 lb-ft of torque, 120-mph trap speeds, and 21 mpg on the highway without dropping three grand on a slick EFI setup? Think again.

The secret? Wideband tuning and adjust-able carburetor fuel circuits that allow you to tune idle/cruise mixture and curves. "Off-road use only" combinations of cam-shaft, cylinder heads, and quench area can become surprisingly docile with some attention to carburetor tuning. Most over-the-counter (OTC) carbs come with a tuning baseline that will run OK in the average car, but not exceptionally well with your specific application. With wideband tuning and careful attention to two key circuits found in most OTC carbs, you realize fuel mileage that rivals that of the latest EFI setup. Yes, having an overdrive to slow the final drive ratio down to the 2.5:1-2.6:1 range helps, but the mileage benefits of a 2,000-rpm cruise can be easily nixed by an untuned carb dumping a 10:1 air/fuel ratio into the motor when 15:1 is nice enough.

Thanks

[Old Truck Man]

A 350 and fuel economy are two words that never will work. You cant make something from nothing. You cannot have cake & eat it too. For every action there is a equal and opposite reaction. There are no magic carburators. Want more HP increase RPM and engine size. Want fuel economy decrease engine size & RPM.

[theastronaut]

Originally Posted by Old Truck Man

A 350 and fuel economy are two words that never will work. You cant make something from nothing. You cannot have cake & eat it too. For every action there is a equal and opposite reaction. There are no magic carburators. Want more HP increase RPM and engine size. Want fuel economy decrease engine size & RPM.

^^^ This is why carbs "can't get good mileage". Their owners won't tune them properly because they think there's no point in it.

I've got as high as 23.8 mpg in my sister's 4300 pound, 400 hp Trailblazer SS with a 6.0 Corvette LS2 and 4.10 gears. I guess that should be impossible too... but GM engineers know how to tune the fuel mixtures. Lean cruise air/fuel ratios can be the same whether you have a carb or efi. Even aftermarket EFI has to be tuned to run right... why not just tune the carb and distributor you already have? It's easier to use a $200 dollar gauge, a pack of jets, a timing light, and a $5 buck screwdriver to tune your engine than it is to tune a $2500+ EFI system.


If bigger equals worse mileage, I guess mine should have dropped when I went to dual 2-barrels that flow 840 cfm on my VW. The VW also has 4.37 R&P... 60mph is over 3000 rpm and it still gets 36.25 on the highway. VW advertised "an honest 25 mpg" so smaller isn't always better. A bigger carb flows more at low throttle input so it stays on the idle circuit longer so they stay leaner over a wider range at low loads if it's tuned right You can run 16-17:1 AFR if you run enough timing to ignite the leaner burn sooner (lean mixtures take longer to burn). I bet 95% of out of the box carbs are running 10-12:1 or richer at light load cruise.

One thing about that article on Innovate's website- 14-15:1 mixtures run the hottest. If your engine is already tempermental about heat then it will run hotter. At 14.7 all the gas and all the oxygen is burned completely- lots of heat. The old saying that "lean is hot" is only half true- at WOT it'll burn a motor up, that's why you want about 12.5:1 at WOT- the extra unburned fuel acts as a coolant. At light loads, the extra unburned air of lean 16-17:1 mixtures will provide a cooling effect, and you're using even less gas than they're recommended 14-15:1. It is a little harder to tune for 16-17:1 since leaner mixtures burn slower; you'll need to add in extra ignition advance while at low loads/idle circuit crusing. Then pull timing out for WOT/higher loads and richer 12.5:1 power circuit mixtures.

[Lee H]

Best bang for your buck to improve fuel mileage is a "real" tune up and carb overhaul. If I use my speedo I average 14.7, If I use GPS it's 12.8. I would recommend a break even analysis before spending money on some of these things. It takes a lot of miles to recoup $2,000-$4000 for EFI or an OD transmission. I wonder if they still sell the Tornado?

[Average Joe]

Like others have said tuning is key here. 10 mpg is not horrible for a small block 'burb but not great either. I think the wideband o2 sensor would be money very well spent. Especially if you have another caburated vehicle to use it on as well. A well built and tuned qjet would also help. Call Sean Murphy Induction for a rebuilt custom tuned unit for your application. Why no vacuum advance? This should get you another 1 mpg easy. A clutch fan or electric would also help. I would not expect a miracle but I think 12 mpg city and 14-15 mpg highway should be doable without overdrive and your current 3.42's if you keep it under 65. Currently Im getting 10.75mpg highway with a low compression 454, TH400, and 3.07's in my 67 'Burb. I think with more tuning and a clutch fan 12 might be possible. Good luck.

[Average Joe]

Originally Posted by theastronaut

^^^ This is why carbs "can't get good mileage". Their owners won't tune them properly because they think there's no point in it.

I've got as high as 23.8 mpg in my sister's 4300 pound, 400 hp Trailblazer SS with a 6.0 Corvette LS2 and 4.10 gears. I guess that should be impossible too... but GM engineers know how to tune the fuel mixtures. Lean cruise air/fuel ratios can be the same whether you have a carb or efi. Even aftermarket EFI has to be tuned to run right... why not just tune the carb and distributor you already have? It's easier to use a $200 dollar gauge, a pack of jets, a timing light, and a $5 buck screwdriver to tune your engine than it is to tune a $2500+ EFI system.


If bigger equals worse mileage, I guess mine should have dropped when I went to dual 2-barrels that flow 840 cfm on my VW. The VW also has 4.37 R&P... 60mph is over 3000 rpm and it still gets 36.25 on the highway. VW advertised "an honest 25 mpg" so smaller isn't always better. A bigger carb flows more at low throttle input so it stays on the idle circuit longer so they stay leaner over a wider range at low loads if it's tuned right You can run 16-17:1 AFR if you run enough timing to ignite the leaner burn sooner (lean mixtures take longer to burn). I bet 95% of out of the box carbs are running 10-12:1 or richer at light load cruise.

One thing about that article on Innovate's website- 14-15:1 mixtures run the hottest. If your engine is already tempermental about heat then it will run hotter. At 14.7 all the gas and all the oxygen is burned completely- lots of heat. The old saying that "lean is hot" is only half true- at WOT it'll burn a motor up, that's why you want about 12.5:1 at WOT- the extra unburned fuel acts as a coolant. At light loads, the extra unburned air of lean 16-17:1 mixtures will provide a cooling effect, and you're using even less gas than they're recommended 14-15:1. It is a little harder to tune for 16-17:1 since leaner mixtures burn slower; you'll need to add in extra ignition advance while at low loads/idle circuit crusing. Then pull timing out for WOT/higher loads and richer 12.5:1 power circuit mixtures.

Great advice here!

[CaptRMW]

1- Lose the Edelcrock carb and get a Q-jet.
2- electric fan
3- overdrive trans.
4- 3.08 gears.
5- aftermarket cruise control.
6- tune carb and ign. timing for max efficiency.

A "good" 700R4 and a Q jet is the best investment you can make just steer clear of folks like Munster sp? transmissions.

[theastronaut]

Originally Posted by Average Joe

Great advice here!

The VW guys that are pretty sharp have been preaching that info for years because its essential on a hopped up VW. They're aircooled so it's easier up combat heat by not making it in the chamber than it is to shed it with added cooling efforts, so lean cruise mixtures are important. Plus the mileage/power difference is more noticeable when the jetting is off in a VW so more guys are into tuning. You've only making 50-60 hp stock and 200-220 on an all-out street motor- the tune has to be right to get the full potential. V8 guys have enough power already that losing power from a poor tune isn't as big of a deal.

[60sIron]

My turn...... Unless I missed it, my only addition would be a vacuum gauge. My Burb has one mounted in the dash. Looks stock. It's a great tool to adjust your driving habits. Now to piggy back on. Is your speedo/odometer calibrated for your tire size? If not you could be doing better or worse depending. Lastly and I've stated it in this forum before. Be realistic, if you're getting 10 mpg what kind of increase is realistic 10, 20, 50%? How many miles do you drive? I have 4:56 gears in my Burb. My mpg would improve with a change but the cost out weighs the gains. Unless I needed to fix something in the differentials anyway then I'm in.
Oh one last thing. You could buy a Prius and use your Suburban to park it in......
I'll stick with poor mpg too....... lol.......

[Old Truck Man]

Originally Posted by theastronaut

^^^ This is why carbs "can't get good mileage". Their owners won't tune them properly because they think there's no point in it.

I've got as high as 23.8 mpg in my sister's 4300 pound, 400 hp Trailblazer SS with a 6.0 Corvette LS2 and 4.10 gears. I guess that should be impossible too... but GM engineers know how to tune the fuel mixtures. Lean cruise air/fuel ratios can be the same whether you have a carb or efi. Even aftermarket EFI has to be tuned to run right... why not just tune the carb and distributor you already have? It's easier to use a $200 dollar gauge, a pack of jets, a timing light, and a $5 buck screwdriver to tune your engine than it is to tune a $2500+ EFI system.


If bigger equals worse mileage, I guess mine should have dropped when I went to dual 2-barrels that flow 840 cfm on my VW. The VW also has 4.37 R&P... 60mph is over 3000 rpm and it still gets 36.25 on the highway. VW advertised "an honest 25 mpg" so smaller isn't always better. A bigger carb flows more at low throttle input so it stays on the idle circuit longer so they stay leaner over a wider range at low loads if it's tuned right You can run 16-17:1 AFR if you run enough timing to ignite the leaner burn sooner (lean mixtures take longer to burn). I bet 95% of out of the box carbs are running 10-12:1 or richer at light load cruise.

One thing about that article on Innovate's website- 14-15:1 mixtures run the hottest. If your engine is already tempermental about heat then it will run hotter. At 14.7 all the gas and all the oxygen is burned completely- lots of heat. The old saying that "lean is hot" is only half true- at WOT it'll burn a motor up, that's why you want about 12.5:1 at WOT- the extra unburned fuel acts as a coolant. At light loads, the extra unburned air of lean 16-17:1 mixtures will provide a cooling effect, and you're using even less gas than they're recommended 14-15:1. It is a little harder to tune for 16-17:1 since leaner mixtures burn slower; you'll need to add in extra ignition advance while at low loads/idle circuit crusing. Then pull timing out for WOT/higher loads and richer 12.5:1 power circuit mixtures.

All the things you have accomplished defy the laws of Physics. You should quit whatever it is you do for a living and concentrate on pepertual motion. There is a old saying that a million dollars is nothing to a liar because they can have as many millions as they want. Yes fuel injection or a finely tuned engine is more efficient. However a gallon of fuel only has a certain amout of BTU,S in it. I have two M farmall Tractors one is gas the other LP both are 248 Cu in. The Lp tractor has much less power than the gas tractor. Because there isn't the BTU in the LP fuel. Other factors like aerodynamics ,terrain, wind, weight & load, transmission & gear ratios have a greater impact on Fuel economy than tuning and magic carbs. I once owned a 66 chev C65 dump truck 366 with a Rochester 4 gc 4 bbl carb from a 250 HP 327 & 5 speed 14 yard dump. Hauled asphalt & gravel. The 366 lost a piston so I pulled a 2 bbl 350 truck engine from a school bus and installed it. The 350 pulled ok however it used over twice the fuel as the 366, so I changed the intake and put on the 4 GC Rochester and the 350 still sucked up fuel. The 350 just didn't have the low end torque and wouldn't pull a load at low RPM. The OP 11 MPG with todays crappy fuel is right in the ball park for a heavy poor aerodynamic designed truck. If a large engine with big valves can be made to get fntastic fuel economy then a lawn mower would burn as much fuel as a 460 cu in Lincoln . You can not get around & bypass the first law of Physics. That law is you cant make something out of nothing.

[Old Truck Man]

Originally Posted by 60sIron

My turn...... Unless I missed it, my only addition would be a vacuum gauge. My Burb has one mounted in the dash. Looks stock. It's a great tool to adjust your driving habits. Now to piggy back on. Is your speedo/odometer calibrated for your tire size? If not you could be doing better or worse depending. Lastly and I've stated it in this forum before. Be realistic, if you're getting 10 mpg what kind of increase is realistic 10, 20, 50%? How many miles do you drive? I have 4:56 gears in my Burb. My mpg would improve with a change but the cost out weighs the gains. Unless I needed to fix something in the differentials anyway then I'm in.
Oh one last thing. You could buy a Prius and use your Suburban to park it in......
I'll stick with poor mpg too....... lol.......

I knew a guy who worked in the chev dealers shop in 73. those trucks all got crappy fuel economy. He was getting a lot of bad negative complaints because he couldn't tune them up and improve the fuel economy. one day the shop foreman came to the rescue. he obtained a number of speedometer gears. they would increase the speed indicated by about 5 MPH. the customer drove a little slower and that helped to use less gas. and the odometer showed a few more than the actual correct milage so the calculated fuel economy was a improved result.

[Old Truck Man]

Ok I have a 81 3/4 that has a 350 engine & 350 trans. I use it for a wrecker & to pull trailers. Now the 350 used a lot of gas. the crankshaft went bad. Im building a 283 with 602 heads from a 305 . stock short block. topped by a cast iron intake and small base Rochester two bbl carb. It will use the 350 single exhaust with a turbo muffler. I hoping for a average of 16 MPH.

[Old Truck Man]

Ok many will laugh but the best carb ive ever used for fuel economy and they are easy to tune. Now get this is it,s a FORD autolite from the sixties. it don't matter if its the two bbl or the 4 bbl. Not the best for high performance but they have a good idle and with the correct power valve & jets they can improve fuel economy. Back when I first started out I tinkered with lots of ford FE 352,s & 390,s and 260 & 289,s. Take out Y blocks and swap in a better mill. I had a 65 ford mustang with a 260 two bbl three speed and a 300 to one rear gear. It was light and still smoked the tires. Handled like crap at high speed. but it didn't use a lot of gas.