Fuel Economy and $4 gas...

[Kixwy2]

First, my specs:

1974 GMC 1/2 ton 2wd CA truck
GM crate 350/260ft lbs torque - stock with 1000 miles on it
rebuilt Rochester quadrajet carb
original manifold with EGR blocked off
new fuel pump, fuel lines, hoses, etc
new distributor and accessories
Timed to 11* BTDC
12 bolt rear
31" BFG All Terrains

and a ghetto dual exhaust system of unknown origin on the list to be replaced...

Ok, so I want to make sure I am getting the best gas mileage I can with this truck. I've tuned the carb so the fuel mixture is good and leaned it out some, but not enough to cause a stumble once it's warmed up. I'm not a pedal to the metal kind of driver, but it seems I'm not getting the mileage I should be. Feels like it's around 8-10 MPG, which sucks. It sounds good, and runs great, but can I get better MPG performance?

Sort of a novice at the timing/tuning thing and I'm willing to take it to a shop if it will help significantly, but also willing to try it myself.

I'm just tired of going 120 miles on a tank of gas. And paying $60 to do it.

Thoughts?

[Restrorob]

Best of luck to ya, Best I ever got out of mine is 10 mpg bone stock tweaking on everything. Now that it's in pieces and the engine rebuilt and stuffed with all sorts of goodies I may be lucky to get 6 mpg. But, It won't be a DD but will spend the rest of it's life on easy street.....

[C-10volvo]

First off, what kind of driving do you do?
Assuming there is a th350 in it, it may be worth while to get a taller gear in that 12 bolt if you are spending time on the freeway. Some other cheap mods like all synthetic fluids in the read differential, engine and transmission, properly inflated tires, keeping the windows up, ans so on may help out a bit.

Now lets all be realistic, a square body isn't going to see much better than 15 mpg ever unless you dump some cash into it or have a mid to late 80's c-10 with a 700r4. Get a beater daily driver, if it has to be a Geo, then so be it. Ive been driving around a red 16 year old cheerleaders car for the past 4 years.

cute huh?

[SBTork]

i'd swap to a smaller tire, but something like that would not make all the difference. I am in the same boat, my trucks setup is almost idenitcal and I get the same mpg #'s. Let me know if anything you try works.

[chevymotocross]

Gearing is going to be your biggest thing to look at considering your engine is well tuned, which it sounds to be the way you described it. 31'' tires are pretty meaty and could be costing you some gas money.

[rfmaster]

Kixwy2

I was facing the same 10-12 mpg with my truck. If you do a lot of hwy driving the 700R4 and a TBI conversion is the way to go. Yes, I know it cost money (been there and done that), but 700R4 are plentiful and a rebuildable core can be had for about $200. They are not as strong as THM-350, but if you are not pulling 8000lb trailers up the Tejon Pass it (after being properly rebuilt) should be fine in your 1/2 ton. Swapping in 700R4 increased my mileage from 10 to about 15mpg. In my case it was a simple swap (no drive shaft cutting because my THM-350 had a 9" tail shaft!)
Carb to TBI conversion got me another 2-3 mpg on highway and much better city mpg (13.5 MPG vs. 8.5). See my sig for details.

YouTube - Carb to TBI conversion

//RF

[draggin86]

sell it and get a 5.3L vortec motor!

[James McClure]

Kix: Do the math and get an accurite number. I have an 84 K20 (see below). I'm older than white dog crap and drive like it, LOL. I get 15 to 17 highway even if I am pulling my equipment trailer (8X17') empty. The only place my specs differ from stock is timing, carb settings & thermostat. I run mine up till it pings a bit on the road and then back it off a touch and I got the carb super lean and a 160 degree thermostat to keep it all cool. jim

[75sierraclassic]

I don't have any other input on how to improve your MPG, just on how much you can afford. If you look at it as a cost/benefit analysis, by improving the gas mileage from 9 MPG to 15 MPG you can save a lot of money per year. Assuming you drive about 8,000 miles/year and gas is at $4/gal, this saves you almost $1400/year in gas money going from 9-15 MPG. Of course if price of gas goes down, or you don't drive that many miles a year this figure will decrease, but for $1400 you can do quite a few things to your truck.
I'm an engineer, so it usually comes down to practicality for these decisions. The operative word being "usually". In my case, I've put way more money into my truck than I'll ever get out, but it was fun!

[rfmaster]

Originally Posted by 75sierraclassic

If you look at it as a cost/benefit analysis, by improving the gas mileage from 9 MPG to 15 MPG you can save a lot of money per year. Assuming you drive about 8,000 miles/year and gas is at $4/gal, this saves you almost $1400/year in gas money going from 9-15 MPG. Of course if price of gas goes down, or you don't drive that many miles a year this figure will decrease, but for $1400 you can do quite a few things to your truck.

Agree, me too - You can only expect the price of fuel to go up. This is due to both China and India rapidly converting from bicycles to cars. There is no excess oil capacity left on world market. Plus, the usual speculators and stupid local regulations calling for more than 25 unique gasoline formulations required for specific markets drive gas prices up.
http://www.ipca.org/top10list.pdf

Originally Posted by 75sierraclassic

I'm an engineer, so it usually comes down to practicality for these decisions. The operative word being "usually". In my case, I've put way more money into my truck than I'll ever get out, but it was fun!

Ditto here...

[Kixwy2]

Originally Posted by James McClure

Kix: Do the math and get an accurite number. I have an 84 K20 (see below). I'm older than white dog crap and drive like it, LOL. I get 15 to 17 highway even if I am pulling my equipment trailer (8X17') empty. The only place my specs differ from stock is timing, carb settings & thermostat. I run mine up till it pings a bit on the road and then back it off a touch and I got the carb super lean and a 160 degree thermostat to keep it all cool. jim

Well the GM crate is in there to stay - I just did the swap and I can't afford another new or used motor, so that's out. And the tires are basically new so I don't see the need to get new ones if it isn't going to affect my economy all that much.

@James: I'd love to hear more on how you've tuned your truck. I put a 180 degree thermostat in the motor when I did the swap... I hope that's enough.

My problem is getting the ratio of carb tuning to timing right. Should I increase the timing, then lean out the carb? If I increase the timing much more, I get a stumble off idle, which is still a problem with the carb. 17 mpg would be awesome!

I agree with the cost/benefit analysis. I got my degree in economics, so I'm all about the good deal, and I would love to save some cash in gas...

[Rooster's82]

Replace your clutch fan with an electric...you get more power and MPG.

[75sierraclassic]

http://water4gas.com/2books.htm?hop=lovekae#info

Burn water.

[Rooster's82]

Originally Posted by 75sierraclassic

http://water4gas.com/2books.htm?hop=lovekae#info

Burn water.

I want to see someone try this...

[piecesparts]

Originally Posted by Rooster's82

Replace your clutch fan with an electric...you get more power and MPG.

Totally agree on the change out of the fan to electric. Look at a better highway designed tire. The 31" tires are hurting your rolling resistance. Ensure the tires are inflated to a good pressure and not running soft. The OD tranny will gain you a lot and the fuel injection will fine tune the air fuel mix. I would also suggest a Multi-spark ignition and a good set of
QUALITY spark plug wires. The hotter spark, the more spark will garauntee the burn of ALL of the fuel in each cylinder and not wasting it on exhaust gases. If the vehicle is lower to the gorund, then the air resistance UNDER the truck would be less and the mileage will tend to be better. What is your exhaust relaly dong for you---is it just making noise or is it actually working to evacuate the engine of waste gases? Look at the air in and exhaust out process and see if it can be optimized.

[babyJay]

Burn water....OMG....that sounds so hokey, yet sooo believable. Click the link and read. LOL

[Thumpin455]

If you dont live in a city, suburbs, have an HOA, or near any other residences you can make your own fuel. If you arent in BFE like myself, you are stuck paying whatever they want to charge you. If you are in BFE I can point you in the right direction.

Being in the peoples republic of California, you cant change much on your truck in regards to the engine. Although a swap to vortec heads, and a mild 214-220 @/050 cam would really help. The more torque your engine makes, the less throttle angle it will need to get moving and maintain speed, you can also change the final drive ratio to lower rpm. Right now if you put a 3.08 gear in your truck it would barely move and would still get crappy mileage.

If you have an engine that doesnt make much torque, be it big block or small block, it will use more gas. I am not implying that an engine that makes 700hp/tq will get 35mpg, just that up to around 500ftlbs with 400ci and larger, and around 400ftlbs with smaller than 400ci engines, you will improve economy. Raising compression also increases economy, at least to a point, when you require race gas then $8 a gallon isnt going to help is it? California makes it tough to do anything to your vehicle, even if its an improvement and makes less pollution, you can fail. Stupid isnt it?

Making it easier for the engine to move your truck will help. An alignment, true the brake rotors, reduce unsprung weight, repack wheel bearings, and aerodynamic improvements will also help.

Simply jetting your carb lean wont help economy, there is a balance to all of this and skewing something all the way to one end isnt going to help. Having it finely tuned the right way will do much more for you. That being said finding someone who can tune a carb is getting quite tough. Most people are absolutely clueless about carbs, particularly the younger generation now graduating from VoTech schools. Most schools are no longer teaching carburetors.

Things to invest in. A tunning kit with metering rods, hangers, and jets, a wide band O2 sensor setup so you can record and tune it yourself, and some literature on carbs and tunning them. There isnt a ton of info on the Qjet that is worthwhile, and a reman is usually a mess with mismatched parts and nothing working right. Knowing how to do it yourself will be your best bet, because paying someone else to do it gets expensive real fast.

If I can squeeze 13mpg from 7.5L with 4.11 gears, an 850 mechanical Holley carb, a 3000 stall, and only a 27" tire in a 3500lb drag car, and 22mpg average on a 1500 mile trip in a 4200lb car with 7.5L, Qjet, OD trans, and around 400hp/500ftlbs tq, then you should be able to get around 15 relatively easy. Its all in the total combination. The drag car ran mid to high 11s in the 1/4 @115 mph, and the other one ran 13.50s mainly due to traction issues, so we arent talking low powered vehicles.

On the flip side my 76 swb has a stone stock 87 454, 700R4 from a diesel suburban, 3.73 gears, and the stock worn out Qjet, havent even changed timing yet, and it is lucky to get 8 mpg. Plans include a cam and intake swap, rebuilding the carb, as in much more than simply putting new gaskets in it, and doing whatever I can to make more torque and improve mileage, even if it means a head swap and rebuilding the entire suspension. Its my summer project, well one of them, and by end of summer it should be running on home brewed ethanol, but I will get the best mileage that I can while its still on gasoline. I may as well keep track of what I do and the changes to mileage and post them here for you guys.

I am pretty much done with the gasoline, being on a fixed income I cant afford it. The VA gave us a $20 cost of living increase this year, so that wont buy much gas. Seeing how I have plenty of time on my hands, but little in funds, its time to find an alternative to paying someone else for everything I need. If that sounds interesting, let me know.

[SBTork]

^^ that sounds very interesting

[flamingbig10]

don't feel bad I'm getting 3-5 miles a gallon, carburetor and timing issues, and heavy foot

[Thumpin455]

Also my economy car is one of these.. 300hp and gets 28-30mpg highway. I really like the LS1 and if I could find another one it would go in the 76 in short order. Just cant find one cheap, so an LQ4 or L92 will have to do... sometime...

[knightlife]

get a 4 clanker like what I did nothing beats getting 22-28 mpg and still being able to get sideways.

[James McClure]

In theory I agree with thumpin. The problem is what do you get for what you give? Using alchol for fuel works, BUT, it only delivers 1/2 the punch and to top that off you will use more fuel making the alchol than you get as fuel. You could use propane. Conversion is easy with injected engines but not so with carbed engines. You'll run into the same power per gallon issue as with alchol though. Propane has the advantage of being super clean and with no octane rating you can pretty much set the timing wherever you want within reason. Unlike gas, propane has little if any ash, so, the oil doesen't get dirty and you can stretch oil changes right out if you use oils like Mobile1. For now, gasoline gives us the most "bang for the buck".
For Kix: I have mine tuned like this, R43TS plugs (cold plugs help with ping issues). Thermostat is 160 degree for the same reason. (180 degree during the winter for heat) I have rejetted the carb to 305 specs and set the float 1\32" low. I use a "purple" power valve spring to take care of "just off idle stumble". Timeing is set at roughly 14 degrees but as I said before I change it as conditions change. When I tune I use ALL GM parts and the cap & rotor get changed every time. Wires get the "spray bottle" test, if I get a skip they get changed. Other than these items, the best thing you can do to improve mileage is "drive with your brain". Use the terain to your advantage, drive at night (denser air, less traffic) "draft" the big trucks when you can, coast down hill, keep the AC off, and biggest issue, keep your foot out if it. Jim

[Rooster's82]

James is right....the best thing you can do is drive smart. If i'm coming up on a red light i let off the gas completely and drift up to the light. This drives FL drives NUTS, everyone seems to accelerate right to the last moment then hit the brakes so they can hurry up and wait...just a huge waste of gas. Also, getting your truck moving from a dead stop requires a lot of energy, if you can keep moving just a little bit until the light turns green or its clear to make a turn it helps.

I had a 1997 s-10 that the fuel gauge when out on, so i had to use the trip to monitor my fuel level...well this has made me absolutely insane about gas mileage, ever since that truck i have calculated my MPG on every single tank i have put in any of my cars. I got super good at estimating my MPG just by thinking about how i drove on my last tank. In my Honda Civic i have gotten a high of 37mpg and a low of 26mpg (right after i got my AEM intake, i loved hearing the v-tech kick in).

Anyway the point of my story is that you can have a 10mpg swing just from driving habits...that is a hell of a lot more then tuning your engine and putting in electric fans and all the other stuff. Of course if you have a well tuned engine, well lubed drive train, and increase the efficiency of power use AND drive like your running off fumes you will see the highest numbers.

[Thumpin455]

James what I am doing wont work for everyone, that is a given. If someone has the resources I have, they dont really need to buy fuel. Yes it takes sweat equity, ingenuity, and some learnin' to do it, but its worth it. On the plus side, if something goes horribly wrong I will still have transportation. (yeah the survivalist in me comes out..lol) People have different situations, but owning trucks there is a chance not all of us are urban, or even suburban. The rural people are the ones who can start a change, and having to drive 20 miles just to fill up isnt a problem city people have.

Driving style plays a huge role in mileage, Rooster and James are 100% right on that. That is why my GTO that gets 20 highway gets 8 city, because I have a heavy foot and an 850 mechanical demon on it right now. Do what you can to make more torque in the lower rpm range where your engine spends the majority of its time, and you will use less gas. Peak hp is nice, but its what the engine makes between 1800 and 3000 rpm that matters most for daily drivers.

About alky for fuel. You can run race car type compression on it, and higher compression is more efficient at least to a certain point that varies with combustion chamber design, displacement, cam timing etc. Also you can run higher boost levels with it, and turbos and superchargers make more torque, if you want to go that route. It runs much cooler, so it is a pain in winter, particularly where I live. Blown alky vehicles actually get frost on the blower in summer just cruising around. So you can build an engine to suit the fuel, and get more efficiency from it in the process.

Please note I am not advocating E85, because that is a different concept entirely. I am referring to making your own fuel as opposed to buying it mixed with gasoline. The idea there is to stretch oil farther, and yes it costs you mileage and about the same if not more than running straight gas. The red Formula I posted earlier in this thread requires premium, at least 91 octane to run right. If I put cheap gas in it still runs but I only get 22-24 mpg highway, so the little bit extra saved on each gallon means I burn lots more of it. Ethanol mix makes it worse, and I am lucky to get 20 from a car that should get 28 on a regular basis. It depends on what the vehicle is set up to run on as well.

Alky wont work as well in a 7:1 or even an 8:1 engine, unless its supercharged, it just doesnt squeeze hard enough to use the strengths of the fuel, its designed for camel pee gas, and will run best on that. Make some changes and you can get better efficiency for a different fuel. Yes changes cost money, and the majority of us here are "enthusiasts" as opposed to people who view the vehicle as basic point A to point B transportation. We justify changes and improvements differently, if we get more power and better mileage, we are happy even if it costs us more than just a new set of plugs and wires, or a new set of tires.

That being said, get everything working its best, including the brakes, U joints, and other forgotten until they crap out parts and systems, and you will use less gas. Keeping your truck running good is preventative, and it will be cheaper in the long run. Elbow grease and sweat equity go a long way with old vehicles, and for most of us it is enjoyable to work on them.

It isnt a race vehicle, but if you treat it like one, at least in the mindset of maintenance and not driving style, it will perform better and use less fuel. If you have a drag car you want it to roll as easy as possible, cut through the air as easy as possible, you dont want any drag on the brakes, and you dont want anything to break while you are going well over 120 mph. The same things that work on a drag car to improve ET and MPH that dont require making more power or connecting it to the ground, will make your daily driver safer and more efficient to drive on a daily basis. Isnt it easier for you to push something on well oiled rollers than it is across rough concrete or through mud? Same with the vehicle, let it do its work easier and it wont burn so much fuel.

This thread has really gotten me thinking about the ignored or forgotten things on our trucks. Maybe its time for some How To threads, and the results.. Its warm now so I dont need the 4x4, maybe I will get the truck legal so I can put this in perspective, pictures, and understandable text instead of these long winded book type rants..

Headed to the shop.

[Poopski]

Buy one of these:555 CID