Increased MPG for carbs?

[OSE_NERO]

Right now I have an '81 C10 single cab, long bed, two-wheel drive model pickup. I'm wanting/needing better gas mileage. I have a 350/350 combo right now, and would like to keep it that way, but if I can't really get any better mpg out of it, I suppose I'll have to swap it with an EFI motor QQ lol

My question is, how can I increase the gas mileage more?

Currently, I'm fixing the previous owner's neglect and putting life back into this behemoth. When I got it, I was probably getting about 6-10 mpg city. I never got to really do the whole calculating thing because I was always stretching the last dollars of my paycheck when I actually HAD work. Now though, I feel like I'm getting better mpg. I've put on an Edlebrock performance intake manifold, a Street Avengers series Edlebrock 600 cfm carb, Edlebrock breather kit and air filter, and have replaced all of the exhaust line, pardon the manifolds (which are next when I get income again). I have a 3" exhaust true dual exhaust line with Thrush Welded mufflers on each line minus cats.

I'm going to be honest and say that I literally have no mechanical incline, besides changing tires, batteries, headlights, and oil. That's only because I worked at Walmart's TLE section for two years. I love cars, and have a lot of stats memorized about them, but you hand me a wrench and I'll stare at you dumbfounded. I won't try to claim that I know anything that I don't, especially with this being the case.

I've been told that a bigger pipe, pardon the massive ones unless it's diesel, will increase both power and fuel mileage. I was also told an X-pipe would help, but not until I had my exhaust already put on. Does it? If so, should I do it when I get the headers put on?

I was also planning on lowering my truck a little bit to get the "bruiser cruiser" look, and to increase fuel mileage. I've been told that a lower stance will help aerodynamically to decrease drag, increasing mileage.

Also, I was planning on putting aftermarket wheels onto my truck (no bigger than 20s, and most likely 18s). I know that these won't effect gas mileage, but I heard that if I changed the wheels I would have to mess with the gearing of the truck since it was built and tested with the 15s. Is this true?

However, I was also wanting more power as well on top of gas mileage, but as of now, those roles have reversed. I've been told that you have to sacrifice one to have the other, but I don't want to believe that. I just want a nice blend of each.

I also just read about modifying the carb to increase gas mileage. However most of those people have "vanished". The way one man described it was that it ran on gas vapors instead of actual raw fuel and that it was more potent that way. Which, to the untrained such as myself, sounds like power while also boosting mpg.

I also know that on TBI and EFI that if you put a cold-air intake on the vehicle, it will give you some power and also increase gas mileage. Is it possible on a carburetor motor? And if so, will it have the same effects?

Lastly, I know that diesels and small tuner engines use turbos to boost power and I've heard that it WILL increase gas mileage and that it WON'T. So which is it? Does anyone know?

If anyone or a few people can help give me some insight to these questions or even suggest other methods (besides converting to CNG as it costs too much for me at the time), I would be thrilled to read them and think them over.

Thanks a bunch.

[cjlinkster]

The first step that I would recommend is to calculate a baseline of your current mileage and you ideal mpg goal. There have been plenty of recent threads on how to increase MPG. Just keep in mind that without an overdrive transmission or running a diesel engine, it's going to be hard to get much more than 15 ~ 17 mpgs.

It sounds like you have your truck already setup very nicely. IMHO the 3" pipes are just about right, I would have done 2 1/2" pipes. The street avenger carb is supposed to have an extra spring to delay the control of the secondaries (for an additional fuel savings of around 5%). Are you running the stock cam shaft? I would recommend a towing cam (which would be a little bit more performance orientated). Headers would help with improving the MPGs but only by 1 or 2 MPGs.

Honestly, (as long as the engine is running properly) a lot of if depends on how you drive the truck.

BTW I am getting around 12 mpg with a 454 (recent tune up) and 4 speed granny. I drive like a man twice my age and keep it under 65 MPH; If I drove like other drivers my age it would be closer to 8 MPGs.

Good luck

[OSE_NERO]

I feel like there's a way to get more than 15-16 mpg. That carb tweak I mentioned, when the guy learned about it from the guy that told him how to do it, told the writer he was getting 150 mpg. I'm just looking to get in the 20-30 mpg range. And I truly believe this is possible, as other stories have surfaced similar to the carb tweak one. Students at Kansas University bought a wrecked F1 car and used the motor in it that was pushing around 890 hp? I think that's what they're pushing, anyways, they took that motor, built their own frame, and crafted a body around it, and it was getting 115 mpg. I feel like I can get my goals with builds like this happening, and still get a decent 300-500 hp.

However, I also have been told what you told me a few times. So I dunno. If I can make it, I can, if I hit what everyone else is hitting, then I'll just have to accept that, haha. Most likely at that point, I'll just switch to EFI and try to increase gas mileage from that motor.

Thank you for your input though.

[cjlinkster]

I think that alot of it has to due to the lack of not having an overdrive trans. Also the efficiency of gas has actually decreased with the new blended fuel.

Even the top of the line new model gas trucks are only getting low to mid 20's MPG (with v6 engines). Diesel trucks get much better mileage and are more efficient with their fuel.

Check out this PM article:

http://www.popularmechanics.com/cars...nt-than-diesel

[foamypirate]

Originally Posted by OSE_NERO

I feel like there's a way to get more than 15-16 mpg. That carb tweak I mentioned, when the guy learned about it from the guy that told him how to do it, told the writer he was getting 150 mpg. I'm just looking to get in the 20-30 mpg range. And I truly believe this is possible, as other stories have surfaced similar to the carb tweak one. Students at Kansas University bought a wrecked F1 car and used the motor in it that was pushing around 890 hp? I think that's what they're pushing, anyways, they took that motor, built their own frame, and crafted a body around it, and it was getting 115 mpg. I feel like I can get my goals with builds like this happening, and still get a decent 300-500 hp.

However, I also have been told what you told me a few times. So I dunno. If I can make it, I can, if I hit what everyone else is hitting, then I'll just have to accept that, haha. Most likely at that point, I'll just switch to EFI and try to increase gas mileage from that motor.

Thank you for your input though.

I'm sorry to burst your bubble, but you will never get 20+ mpg in one of these trucks unless you go LSx with EFI or 6.2L diesel. You MIGHT crack the low 20's then, but that's it. The story about getting 150mpg? 100% complete and total BS. Pure and simple. Never going to happen.

The 115mpg chassis with 890HP? Sure, if you have a custom body with a super low co-efficient of drag and run the motor in it's most efficient range around a track without using the throttle after initial acceleration. But in a 30+ year old truck? May as well drive a barn door down the road.

I'm sorry, but your hopes and optimisms are just completely outside the scope of reality. With some tweaking and fine tuning, proper gearing, and a healthy engine, you MIGHT be able to pull down 17-18mpg on the highway, but your city mileage would suffer. Then, at that point, you have to ask yourself...how much money did I just spend to get 2-3mpg more out of this motor? Many times, people get so caught up in the mileage numbers, that they forget about cost and return on investment. If you spend $3000 to increase your gas mileage by 2mpg...It's going to take a looooong time to break even.

Let's break it down:

12,000 miles a year
15mpg
$3.75/gallon
That means you'll be spending $3000/yr on fuel ((12,000mi/15mpg )* 3.75)


12,000 miles a year
17mpg
$3.75/gallon
That means you'll be spending $2647/yr on fuel ((12,000mi/15mpg )* 3.75)

You'll save, on average, $353/yr. But you spent $3000 to gain those few mpgs...

It will take 8.5 YEARS to break even on your investment. It would be better to just accept your current mileage, or whatever you can gain from simple tweaks, and just run with it.

[GM-power]

[OSE_NERO]

My grandpa's doesn't. His is a 2004 F-250 King Ranch and he's only getting 11.3 or 11.8.

He had a cold air intake on there and it gave him 2 more miles per gallon, but his warranty wouldn't let him have it on there or it would void it. However, he also forgot to keep it, so someone got a free cold air kit, haha. I've thought about ditching my 350 turbo for another tranny. If I did that, I'd like to get a 5 or 6 speed. Do you know of any that can mount up to an old motor like mine? Are there adapter plates for that? Or would I just have to replace the motor if I wanted a tranny like that?

[OSE_NERO]

My grandpa's doesn't. His is a 2004 F-250 King Ranch and he's only getting 11.3 or 11.8.

He had a cold air intake on there and it gave him 2 more miles per gallon, but his warranty wouldn't let him have it on there or it would void it. However, he also forgot to keep it, so someone got a free cold air kit, haha. I've thought about ditching my 350 turbo for another tranny. If I did that, I'd like to get a 5 or 6 speed. Do you know of any that can mount up to an old motor like mine? Are there adapter plates for that? Or would I just have to replace the motor if I wanted a tranny like that?

[GM-power]

The 350 is a popular engine and has been around so you have a decent tranny selection. What gears you got in your rearend?

[86c20]

in the city with my 86 i get 14-15 but that is where i live not really city. same as my dads 97 ram 2500 on the highway tho it is diff i get a constant 21 or better at speed with no overdrive and mine weighs in at 5200lbs and stock hight with bfg at's on it.after 80 tho it drops fast. my motor is a crate 350 with stock q jet. have been told that the air dams help alot. as far as diesel there are guys in the mid to uper 20's with isb's and 4bt's. 6.2 that i have got me 21 at 75 on FLAT land hills killed it

[THE "10" SILVERADO]

Think about it, your driving a giant barn on wheels, well about the same shape. You also do not have computer sensors and gadgets to regulate anything, most carbs act like a water hose with gasoline for the engine. Unless you go with a late model computer controlled engine I doubt you will make it to the high teens. The most I have read on here about mpg's was 17-18, but I think they had an overdrive trans.

Good luck though, I'm trying to squeeze every bit I can outta mine.

[clinebarger]

Originally Posted by OSE_NERO

My grandpa's doesn't. His is a 2004 F-250 King Ranch and he's only getting 11.3 or 11.8.

If a 6.0 PSD is still running after 50,000 miles is a miracle

[Redcap]

In my Malibu and if I drive nice, I can pull 20-22mpg with a smallblock.

My K20 with the 454? 11-12mpg with 4.10s and 35s.

[andrewmp6]

Just so you know a f1 car avgs 3.1mpg some one is pulling your leg big time.Take a look at http://www.popularmechanics.com/cars...-finalists-won Its 840lbs with 40hp that's what a real 100mpg+ car is.

[Edahall]

Originally Posted by OSE_NERO

Lastly, I know that diesels and small tuner engines use turbos to boost power and I've heard that it WILL increase gas mileage and that it WON'T. So which is it? Does anyone know?

Adding a turbo to a diesel engine usually decreases solo fuel economy but helps with heavy pulling fuel economy since the engine doesn't have to struggle so much and blow black smoke.

[OSE_NERO]

Originally Posted by andrewmp6

Just so you know a f1 car avgs 3.1mpg some one is pulling your leg big time.Take a look at http://www.popularmechanics.com/cars...-finalists-won Its 840lbs with 40hp that's what a real 100mpg+ car is.

Ok, so I finally found it, and it turns out they used a carbon-fiber F1 chassis and an electric driving system. It hits 300 mpg though, which is still pretty cool.

And so what about my bubble? I'm still optimistic that there is something out there that can break 18mpg for us "barn doors".

On top of that, I also feel like the stories of getting those huge numbers off of modding the carb are true, since I've heard them from a few places even when I was growing up. My grandpa even knew a guy that did the conversion himself and saw similar figures, and did so for anyone that paid him for his time to do so, but he lost contact with him a couple decades ago it seems.

The whole idea is plausible. I mean, the entire "theory" is that it uses fumes, which are much more potent and easier to consume than raw fuel. If you've ever lit alcohol on fire, it's the same thing. The fumes are so flammable that the liquid never catches on fire. The flame actually just causes the alcohol to evaporate and burn above it.

Think of it another way. You hear of houses being soaked in gasoline and lit on fire. What happens? It burns down. Then you hear about a gas leak in another house. What happens when a flame is introduced? A cinema worthy boom.

Besides, if it doesn't work, then I'll be where I'll be. If it does, then huzzah! I've done it.

[OSE_NERO]

Originally Posted by clinebarger

If a 6.0 PSD is still running after 50,000 miles is a miracle

Hurray for the Powerjoke! lol

[Billett]

There is something that can break 18 mpgs in these. An ls swap and a double overdrive. Not much short of that though... A turbo can help improve economy, but only if you drive it that way. Your best bet is to tune the carb properly, keep your fluids clean and full, check your tire pressure, grease EVERYTHING, and drive it like your grandmother. And I'm sorry to say, but there is no magical carb tune thing that turns gas into fumes and nets over 100 mpgs. If there was every car manufacturer in the world would be doing it stock.

On a side note my fiance's Honda Civic Hybrid gets over 40 mpg. You could always spend all the money you'd put into an EFI setup into buying a more efficient car...

[Edahall]

Originally Posted by OSE_NERO

I'm still optimistic that there is something out there that can break 18mpg for us "barn doors".

Well it is possible to hit 18 mpg on a carbed truck. My 1972 GMC, 1/2 ton, 4x4, 350 cu in, did even better than that and that was in the early 80's. Here's the formula.

1. 3.08 gears
2. SM465 4 speed manual
3. P235/75/15 tires
4. SP2P Edelbrock intake manifold (small diameter intake runners)
5. Rhodes lifters
6. High lift / short duration cam
7. Quadrajet carb (leaned out for best fuel economy)
8. Carb spacer
9. Timing advanced
10. Water Injection
11. 55 mph

For even better fuel economy, I would use Vortec heads so I could run more compression and more timing advance. The Vortec heads should be good for an additional 1-2 mpg. Also, for highway driving, 2.73 gears would even be better.

[Edahall]

For the 1990 Suburban listed in my signature, I'm getting on average mid 20's with that setup. At the price of fuel these days, it has already paid itself off.

But my 1982 Suburban 6.2L diesel (1/2 ton, 2x4, 3.08, 700R4) does even a little better. With some help from some exhaust headers, fuel economy is in the upper 20's. I even got 31 mpg one time on a long trip being very careful with the gas pedal.

[Billett]

Unrelated to the main post but Edahall: I always considered going with a GV unit or a 6 speed to gain some more drivability, but I never considered both. Whats the OD gear ratio on that thing?!

[Edahall]

Originally Posted by Billett

Unrelated to the main post but Edahall: I always considered going with a GV unit or a 6 speed to gain some more drivability, but I never considered both. Whats the OD gear ratio on that thing?!

Gear Vendors OD has a ratio of 0.78. With my 6 speed manual and Gear Vendors combined, the final ratio comes out to 0.546. This puts the engine RPM at 1251 at 60 mph.

[Billett]

Gotcha, I think for the money I'll do a t-56 magnum for the 0.50 ratio, but that is a rock solid setup for sure! Wish they did a GV for the T-56...

[Edahall]

Originally Posted by Billett

Gotcha, I think for the money I'll do a t-56 magnum for the 0.50 ratio, but that is a rock solid setup for sure! Wish they did a GV for the T-56...

Don't know if that would hold up to a Cummins putting out 1000+ ft lbs of torque at 1700 rpm's though.

[Billett]

I know what you have in your truck, I said I would do a T-56. I definitely wouldn't put one behind a well built diesel, but I only have a 350. I just know that they make GV units that match up to a lot of the GM 4 speeds, but the ratio's for OD aren't what I'd like to get. I'd never looked into anything more than a 4 speed with it though. If your 6 is right around the same then it isn't worth it to me, but again, mine's only a 350.