Increased MPG for carbs?

[foamypirate]

Originally Posted by OSE_NERO

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.

Just so you know, that's how every carb on the planet works. You don't just pump liquid fuel into the cylinders, the carb atomizes the liquid fuel (turns it into "fumes") by using a a venturi and engine vacuum.

[spencer_41188]

just find a 700r4. all youll need to do is move your trans crossmember back about an inch shorten the drive shaft and put the tv cable on.

its a lot cheaper then a gv unit

ive built my engine light and full roller just to save fuel. i got fuel injection and a 5 speed headers, h pipe, i went from 4.10 to 3.73, and i have 4wd
i get 20mpg highway easy even with a 1 ton the old lock out style front ends they work wonders

all i really wonted to do was go on the highway and i wonted 4wd, i was able to do that with just the transmission and adapter. i was only getting 12mpg ... i only got 1 tank and long trips changing elivation is not too easy to do with a carb so i put efi on it and the gear change was just a why not.

[kwin]

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.

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?

You may as well take that statement right out of the conversation, the Fords have awful fuel economy. I worked as a fleet manager for a while for a small shipping company , the fords use substantially more fuel that the dodges the duramax is in the middle between the two

[kwin]

Originally Posted by 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.

I have a neighbour who regularly drives from western ontario to Northern Alberta with the same set up you listed ( 6.2 700r4 3.08 2wd) and he gets the same 29-32 range on his trips. He is 70+ and drives like he is 90+ , but he gets amazing economy.
Nice suburban too.

[Firebirdjones]

Originally Posted by 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.

To start with, I'd prefer a quadrajet over that Edelbrock. Edelbrocks require their own calibration kits for any tuning. Speaking of which, the only real way to dial in any carb is with a wideband, otherwise you are shooting in the dark. That coupled with a correctly curved distributor will yield some gains in MPG. I shoot for a leaner 15.0 AFR for very light throttle and idle conditions, while still maintaining a safe 12.8 AFR under heavy load. And I generally go for about 16 initial timing with 20 degrees of centrifical built in for a total of 36,,,should be a good starting point for most engines give or take a few degrees. Then dial in about 12-14 degrees of vacuum advance with an adjustable unit, and hook that to manifold vacuum.

Done this way will give you the best all around performance and fuel economy you could expect from any engine. From there it's all basic stuff. Free flowing exhaust with an X or H-pipe, long tube headers, a good dual plane intake will all help.

Then attack all the HP dragging rotational weight. Dual electric fans will free up some HP and mpg over a mechanical fan, aluminum driveshaft is easier to turn. Lightweight wheel and tire package is easier to turn, then pay attention to the size and the tread pattern as these can affect mpg as well. You could go as far as lightweight viscosity oils throughout. A good working fresh air intake system is free HP. Basically anything you can do to make life for the engine easier will generally return you with MPG gains. You can really get nit picky here, but it all adds up. There is much more to do as well.

I get a respectable 14 mpg out of my 79 1 ton with a 502/400 turbo and 3.73 gears in a truck that weighs 5500 lbs. with some of these tricks mentioned. It cruises nicely at 65 mph at 26-2700 rpms. That's through a power robbing 400 turbo and that huge 14 bolt full floater.
I am doing a custom aluminum radiator with dual electric fans, a gear vendor overdrive unit to drop cruise rpm 3-400, and will eventually go to a lighter wheel/tire package. Currently the 16.5's weigh 65 lbs. each with E load range tires on it I should gain an easy 2-4 mpg with all these changes and put the truck nearly at what some of the new trucks get for mileage. Respectable for a 500 cube gas engine with a carb

My 72 4x4 blazer with a 6.0/4L60 swap gets 22 mpg with 3.73 gears and 33" tires, it weighs 4600 lbs. I run a lightweight wheel, and kept the tire width to 10.5", and a mild tread pattern (BFG all terrains) all help the rotational mass and rolling resistance. I also did dual electric fans on this swap, and I have a sharp custom tune in it using HPtuners and a wideband. That's the sweet part with this EFI, you can fine tune the fuel tables as well as a few other little tricks. Alot of my gas mileage with this rig is in the tune.

You can get upper teens in these old trucks with a carbed 350 using alot of these tricks and a sharp tune, with the right gearing and tire size. But it's going to cost money to do it. Whether it's worthwhile is up to you. That depends on what you plan with the truck, and how long you are going to keep it.

[mrjata]

Lots of good ideas here. I have learned over my 40 some years that if you start by optimizing what is there first is a good place to start. I am a huge fan of Taylor wires! For these trucks, Spiro Pro wires are the way to go. VERY low resistance and no radio noise (and cool colors if that is what you need). I would NOT do a cool air intake, that will hurt mileage. I would actually let the motor take in the warmer air from the motor. Open elements are cool if it doesn't rain. K&N or like that is great for flow.

Not a fan of carb spacers. A good dual plane intake, either stock or raised is fine. Go with Performance Distributor module and coil! This is a must. But you better have the Taylor wires I mentioned. Stockers will explode!. Gap plugs at about .050-.060, really! The ign. upgrade is good for a few mpg. I do this on all the trucks/cars I have had. Going to Taylor wires on my 2012 Silverado as soon as the motor is broken in. My 2005 Silverado 1/2 T got 27.2 mpg with a 5.3. That is 65mph on the hwy.

Carb is up to you. Just read your plugs, this is huge! Very little color on the insulator is what you want, lighter than cardboard. I have run Holley a lot over the years, all sizes and configs. The one that had the best milaeage was the 4010 body style that they dropped. BUT! Summit picked up the casting rights. Take a look. the whole top comes off. No gas spill changing jets. They have annular discharge boosters rather than the down leg or "dog" leg boosters (i.e. more efficient). The regual Holley guts work except the top body gasket. No other gaskets are below the fuel level. Cool huh?

On the dist, I always ran the manifold vac. and not ported. On a 350, I run about 34-36* of total advance all in by 3500. Depends on what your motor/cam likes.

Was playing with converters, a 2500 stall works great on the street. Get a Gil Younger valve body kit for the 350TH. They run cooler, no slip, last for ever. Oh ya, add a cooler always.

this is getting long... Have heard about running synthetic lube in the rear end, just not made up my mind there.

the bottom line? Drive like an old man, take your time, keep the right foot light and gradual. If you need to be there 30 min. ago, you should have left earlier.

Keep up the great site!! I have open ears, let me know what works for you, please!!

[OSE_NERO]

Thanks for all these ideas guys! It's interesting to read all the different styles to get to the end result. However, I'm thinking about saving up for either an EFI engine swap, or buying a custom built 383 Stoker from Unlimited Performance. They're priced at $8,200, and are built to exactly what I ask them to build it for. And it comes with 380 hp and 440+ ft-lbs. of torque. I might even see if they can take that and EFI it as well.

One day, I'll also find something to cram one of their 572s in. $19,200 built from scratch and has 790 hp. Pretty sure that'll be my midlife crisis, haha.

[mrjata]

I built the 383 stroker, for the money, I wasn't that impressed. Seemed like a lot of work for very little. In what little I have done, the heads are everything! The cam, well, duh, sure. It really depends on where you want the torque to come in and the $$$ too.

Guess I am to old school. I like my Holleys. I can tune them to do whatever I want. I like the throttle snap that I can get that EFI can't. Seems like there is just a little delay on the efi stuff. Guess I have tinkeritis too. Think it is a guy thing, really.

Had fun with the emissions test once too(off topic). They said my 52 5 window p.u. with a 410 wouldn't pass the smog test. Legally, I don't have to. I have to meet EPA emisions that were required in 1952. In Missouri, we don't have smog tests anyway, this guy was being a jerk. I went home, switched carburetors, put a barrel of alcohol in the bed. Since I ran a racing fuel business, it was not a big deal. Went back, told him to "sniff this". He plugged in his stuff, I started the truck and "gassed everyone in the building! The were all running out, gasping, wiping their eyes. I laughed my head off. I passed the test!! They told me to take it home and not come back. One officer asked me to launch it hard once. Told him I didn't want the ticket. He threw his badge in the car and told me to have at it. I pulled out on the street, dumped the clutch at about 4500 and picked up the front end and carried it through 2nd gear and let it down. The officers all just waved at me.

This little stunt of just 60 miles round trip cost me a barrel of alcohol ($165) but they learned their lesson. It was a blast too seeing everyone scatter!!

Have fun, enjoy the life and the pursuit.

d

[INSIDIOUS '86]

A simple a/f meter and some good tinkering on a carb will net the same mileage with a carb vs efi

Also 9k for a 383 crate engine??? That sh!t better be putting out 600hp. 380hp and 440 tq can be put down by a vortec 350 with a 268 cam and headers. That's about 2k
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[Redcap]

Originally Posted by OSE_NERO

Thanks for all these ideas guys! It's interesting to read all the different styles to get to the end result. However, I'm thinking about saving up for either an EFI engine swap, or buying a custom built 383 Stoker from Unlimited Performance. They're priced at $8,200, and are built to exactly what I ask them to build it for. And it comes with 380 hp and 440+ ft-lbs. of torque. I might even see if they can take that and EFI it as well.

One day, I'll also find something to cram one of their 572s in. $19,200 built from scratch and has 790 hp. Pretty sure that'll be my midlife crisis, haha.

Wow. Those guys are WAY overpriced.

[76Charlie]

You guys are thinking too hard...hypermilling!!! Go to about 55mph, turn of engine coast to stop light, turn engine back on

[kwin]

Originally Posted by INSIDIOUS '86

A simple a/f meter and some good tinkering on a carb will net the same mileage with a carb vs efi


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Your right, a good friend of mine who is a gm asap tech, one of the old school guys who worked at a dealer says that a carb properly set up can out perform a efi set up, his vehicles always have been amazing with holleys and quadrajets .
He does say the quad is a better more fuel efficient design.

[Firebirdjones]

The Quadrajet will return better mpg for a few reasons. The front primaries are smaller, a very efficient booster design atomizes the fuel, and the metering rods offer very fine fuel metering.

Without a wideband AFR to do your tuning with however,,,you are basically shooting in the dark. With the right lean part throttle adjustments made using a wideband, you can get great mileage out of most any carb,,,some are more involved to deal with, but the end results are similar.

EFI shoots for a target 14.7 AFR all the time unless you are in PE mode (power enrichment).

You can shoot for this same AFR using your wideband and in some cases even a little leaner doesn't hurt anything on light throttle cruise, light load conditions. Some tuners have gone as far as 15.0-15.3 AFR for light cruise applications and pick up some MPG. I've flurted with 15.0 on some of mine, and it's been fine for years. On my 502 pickup however I prefer to keep that one slightly on the rich side (14.2-14.4) at part throttle because I use it for towing heavy loads. At low vacuum conditions (half throttle or more) when towing up hill or pulling away from a stop, the power valve opens and quickly richens it to the low 13 AFR range, and full throttle is at 12.7 AFR, like I said, slightly rich but I feel it's better protected from detonation this way while towing.

The problem now though is ethanol in the gas. The more ethanol in the fuel the richer the fuel mixture has to be to make the same power. Even 10% will change the AFR .3-.4 tenths so there is a fine line there,,,and then it gets more involved depending on where you fuel up the car. Not every station carries the same amount of ethanol. I've seen them carry as much as 17% using a little ethanol test kit. So gas mileage, (and you tune) will change from one fillup to the next.

As far as a carb working better than an EFI is up for debate. The advantage EFI has here that I find tuning my LS engines, is the very fine detail fuel adjustments that I can make in the fuel table cell blocks which creates an entire graph or fuel curve. I can make it do what ever I wish and get some pretty darn good fuel mileage out of it with a key stroke. The adjustments are infinate. On a carb there can be certain areas that you'll have to fudge and live with where the AFR dips or jumps around,,,unless you run a very expensive carb that has adjustable air bleeds, adjustable power valve circuits etc....and it gets pretty involved.

However it has been shown on the dyno with the same engine that a carb still makes more HP and torque by a very slight margin.

They both have good and bad points.

[kwin]

In all fairness he was comparing late 1980's early 1990's fuel injection, Throttle body to carbs not the more sophisticated systems that we have today.

[bnoon]

Originally Posted by kwin

He does say the quad is a better more fuel efficient design.

MPG with a Quadrajet is better than Holley because of the tiny primaries and HUGE secondaries vs the Holley's all 4 bores being equal sized. Keep those secondaries closed on a Quad and you can pull more MPG out of it vs throttle body for much the same reason (TB has two large bores to flow the same air WOT as a Quad).

[Firebirdjones]

Originally Posted by kwin

In all fairness he was comparing late 1980's early 1990's fuel injection, Throttle body to carbs not the more sophisticated systems that we have today.

Is there any other kind??

Unfortunately throttle body injection is so outdated, it's not even a comparison anymore. Not that great of a design either. I tossed the tuning software for that stuff a long time ago,,,very primitive computer that doesn't have much "fine" adjustment. Burning chips is a thing of the past nowadays, very few tuners out there even mess with it anymore, and I figured I'll never own another TBI and I rarely had a customer with it. Even the Multiport stuff starting in 86 was only slightly better thanks to the individual injectors per cylinder, but it still had a primitive batch fire system running it.

When OBDII took over it's pretty much been the mainstay of fuel injection systems since. Even Edelbrock and FAST make an excellent fuel injection setup I'd take over a TBI setup.

[king-918]

Originally Posted by OSE_NERO

Thanks for all these ideas guys! It's interesting to read all the different styles to get to the end result. However, I'm thinking about saving up for either an EFI engine swap, or buying a custom built 383 Stoker from Unlimited Performance. They're priced at $8,200, and are built to exactly what I ask them to build it for. And it comes with 380 hp and 440+ ft-lbs. of torque. I might even see if they can take that and EFI it as well.

One day, I'll also find something to cram one of their 572s in. $19,200 built from scratch and has 790 hp. Pretty sure that'll be my midlife crisis, haha.

8K? Never mind your in the B.A. but hell I sell you my 350 400hp. Roller for 6k lol!
Build your own and know whats in it
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[OJ1988]

Interesting thread. I too am searching for more milage. I am thinking of swapping my 3:73's to something a little higher.

[Firebirdjones]

Originally Posted by OJ1988

Interesting thread. I too am searching for more milage. I am thinking of swapping my 3:73's to something a little higher.

I think everyone is searching. Seeing the direction this country is going, it won't be long before we are paying more than $5 a gallon at the pump in the next couple years. Need to make these cars/trucks as fuel friendly as we can if we want to keep enjoying them.

[OJ1988]

I drive my truck everyday. I've done a big to try and make it more effecient.

Next move is to swapfrom 3.73s to 3.07's.

I also have a tpi setup on the shelf, but need a different base, or different heads.
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[INSIDIOUS '86]

You can take the ethanol out of gas with water btw

Look it up
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[king-918]

Some one should just make fiberglass quarter panels
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[INSIDIOUS '86]

Originally Posted by king-918

Some one should just make fiberglass quarter panels
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VFN fiberglass does cabs bed doors....
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[clinebarger]

LS swap....

[76Charlie]

Originally Posted by clinebarger

LS swap....

All day