tips for better MPG

[1972BlueC20]

I know these trucks are not bought for their fuel efficiency, but I'm getting between 7-9 mpg per tank. My truck needs a new sending unit, so Im having to watch the miles instead of gas gauge. I got 109 miles down with 14.3 gallons burnt LOL

Any tips on getting a little better MPG out of this thing?

I've recently done a full tune-up, converted to electronic ignition, got the timing right, changed the oil, air filter, PCV value, tire pressure is good....any other things I can do?

Again, I don't really care about the gas mileage, this is not why we drive these beasts but if I can save some extra $$$ that's more that I can dump back into her!

[Norcal72]

Stay out of the secondaries. Lead foot eats mileage.

[Mattys1970C-10]

a big ole turbo with a long spool would help

[JointTech]

put it in neutral going down hills.

[i82much]

Buy a wideband O2 sensor, an adjustable vacuum advance, and get to tuning. Your cruise AFR should be about 15:1 for a safe tune that will get you decent MPG, probably on the order of 50 degrees total advance at cruise (initial + mechanical + vacuum). Those are, of course, ballpark numbers.

[LSUMurse]

I've done a lot of research on here and most of the tips are going to be for better highway mileage for instance HEI (I squeezed out 1 1/2 mpg better highway), headers (supposedly), rear end gears (the debate's still going), electric fans, etc.

Apparently the only way to really see any gain is to drop in a newer style injected engine. Even then, the front end of these trucks limits any large mpg gains. I have seen where someone said that lowering the truck gave him some better mpg.

[Lee H]

If you have a quadrajet I would be getting it rebuilt by a professional (SMInduction or Ruggles). If your speedo is off as far as mine you might be getting more than you think.

[69GMCLonghorn]

Check the accuracy of your speedo as suggested above. And then I'd look at the carb for an underlying problem. You should at least get double digit mileage.

[leftybass209]

A vacuum gauge can help you manage your fuel efficiency. Also, what trans and rear gears do you have? A cheap swap to OD be it auto or manual can net a few more mpg's at higher speeds if you can make it cost effective. Less weight helps, as well as lightening the rotating mass but that usually costs much more than it saves. A properly tuned engine in good working order really is your best bet. Any reduction in friction helps too, but again, more money than gains.

[Fitz]

One of these will fix your MPG problem really quick!

[67ChevyRedneck]

Engine/trans/axle ratio. Carb set up too. 7-9 is pretty horrible, unless you have like a big block 4.56 geared truck. I got 11 with my 250/3spd/3.73 and I romped on the poor girl (was 16 at the time).

I now have a 350/700R/3.73 and get 12 around town and 16 highway.

Have you used a GPS to verify miles?

[trac209]

Other then a ls swap or a od trans it's really a matter of fine tuning as said before but it's really not going to be stellar no matter what. Even 15 mpg is a pig to drive in this day and age. I get no where near that myself either. I reside myself to the fact if I want to get good Mpgs with my truck I leave it shut off in the driveway. My neighbour installed a gear vendors od unit in his f100 hoping for 18 Mpgs in the city and it came close but all said and done it was $4000+ To get it done.

[69GMCLonghorn]

Also can we get some details as to what engine/tranny you have, what rear end gears, tire size? Maybe some of us can give you a ballpark of what MPG to expect based on your set up...

[DreamRyder1963]

In my 71 with a 350 three-speed and 3.07 gears, I got 13 mpg combined. I probably will get slightly better this week since last I blew a tire off and limped to the nearest safe spot. In reality I don't expect better than 15 or so for the simple fact that it is a truck. My 93 tbi 4.3 Sierra only gets 15.

[69GMCLonghorn]

Originally Posted by trac209

Other then a ls swap or a od trans it's really a matter of fine tuning as said before but it's really not going to be stellar no matter what. Even 15 mpg is a pig to drive in this day and age. I get no where near that myself either. I reside myself to the fact if I want to get good Mpgs with my truck I leave it shut off in the driveway. My neighbour installed a gear vendors od unit in his f100 hoping for 18 Mpgs in the city and it came close but all said and done it was $4000+ To get it done.

Gear Vendors have a great product going (I almost went with them on my last truck). But really, for the money, just upgrade to a Tremec 5 or 6 speed and not have a funky set up.

[1972BlueC20]

Well I downloaded an app on my phone to check the odometer and it's accurate within a tenth of a mile, so that's not the issue.

I'm running a stock 350 engine (with the exception of a newly added Edelbrock 600 CFM performer series carb and air cleaner) and running though the stock TH350 transmission....I'm not sure about the rear end gears. I'd assume they are whatever came stock on a 72 C20 custom camper with 350 engine and TH350 trans.

I've ran through 3 tanks of gas since I bought her, first tank was 8.23 mpg, 2nd was 9.4 and 3rd was 7.6

[1972BlueC20]

first tank was on the stock quadrajet (needed rebuilding badly) other two tanks where with the edelbrock. 2nd tank was before tune-up, and 3rd was after tune-up.....so I've got my worst mpg after doing the tune-up LOL

[i82much]

Do you have a working exhaust crossover, thermostatic air cleaner and functional heat stove, functioning vacuum advance, and functioning thermal fan clutch?

[DreamRyder1963]

What do you gain from the fan clutch? I know that you should pick up a couple of horse and maybe some mpg but I have never seen any data from it.

[i82much]

Originally Posted by DreamRyder1963

What do you gain from the fan clutch? I know that you should pick up a couple of horse and maybe some mpg but I have never seen any data from it.

Spinning a mechanical fan at 100% draws a lot of power, plus it slows down your warm up time if you don't have the thermostat type.

[DreamRyder1963]

Originally Posted by i82much

Spinning a mechanical fan at 100% draws a lot of power, plus it slows down your warm up time if you don't have the thermostat type.

Is there a noticable diffence in milage or horsepower to warrent the time and expense of a conversion? I know the theorical result but I have not ever seen something to back it up. I don't want to put the money into a fan clutch if it will give minimal results.

[davepl]

Stock you should get at least 10-12 MPG in a city/hwy mix. None of these little things will make up the 3-4 MPG but maybe all of them together might, hard to say.

Probably the best investment would be to weld in an O2 sensor bung and run a gauge for a while. Has to be a wide-band of course. You'll see if its rich at cruise, at what speeds, at what loads, and so on. Then you can tune the carb. Of course the carb has to be RIGHT beforehand.

Ruggles would be nice, but he was 6+ months out last I checked. Carb Connection in Kirkland WA talks the talk, but I haven't driven the car with it yet.

[i82much]

Originally Posted by DreamRyder1963

Is there a noticable diffence in milage or horsepower to warrent the time and expense of a conversion? I know the theorical result but I have not ever seen something to back it up. I don't want to put the money into a fan clutch if it will give minimal results.

I think it depends (1) on how much you drive and (2) whether you do a lot of cold starts. I have done a bunch of google searches on it and yeah, you see guys saying they are getting 2 or 3 mpg. On the other hand, there are guys thinking they are getting 25 horsepower from a cold air intake on a Honda Civic. That's the internet for you.

I don't have any valid scientific data for you. I can tell you that turning that big old fan sure seems to take a lot of effort. I am in the process of replacing the flex fan on mine with a fan clutch, but at the same time I am replacing the exhaust, changing out the points for an electronic module, changing the carb and intake, and adding the heat crossover valve to the exhaust. I expect all of that to make a substantial difference in fuel economy once it is all said and done, but I will never be able to quantify how much difference the clutch fan itself makes given all the other changes.

[RManson]

I got 21mpg in my '68 longbed with a 307ci backed by a T5 transmission. Holley Avenger EFI setup, MSD Pro-Billet distributor, 3.73 rear gear, 27-inch tire. That's highway, city was around 18 or so. I would think that's about as good as it gets using a SBC and not doing a bunch of drastic things.

I think the easiest and biggest improvement would be either an OD trans and/or an EFI setup like the Avenger. Bolts right up to a four barrel intake manifold.

Wonder what some of the LS setups are producing when it comes to MPG?

[Dunenutt]

A while back, I saw some dyno numbers that had a fan pulling 20+ HP. FWIW