Ihad a 390 and a 360 ford v8 awsume power in my 69 f150, but ran less that 8 mpg no matter how I drove it. I would say to get 20mpg first your going to have to find a 12 mile long hill get to the top shut it off and let er roll, the the last 8 miles turn the engine back on. no I really dont think you will reach 20 mpg out of a 390 if you do post it in the top of the forums you broke something that has never been done. not only do you have a very heavy truck you have one of the heavest engines put in anything that it also has to push down the highway. but most of all you have the the power to make anyone wish they had. be cool swapping that new ford v6 into a older f150 with the new 6 speed overdrive have to see that done. good luck

 

In my old 360, the best i got was like 11-12. When i rebuilt to the 390 i got like 14-15. the 4x2 will probably habe to get a new front fiberglass clip, lower the front for less drag, put some 3:00 gears in the rear. headers exhaust will probably help. Maybe down grade to like a 600cfm carb. get some aluminum heads... haha... and then i might be able to get like 18... on freeway of course cruising at 55-60.

 

actually i moved to az in april/may...

I'm going back up for the holiday to visit family from the 20th-28th.... then im flying back to phoenix.
then on the 29th im going to drive to san diego to go see the Ducks play in the holiday bowl against oklahoma..


GO DUCKS!

 

My dad's 70' short bed with a 302/3 speed (when it was on the road) was getting 17-18 as an average with some city and some hiway driving. He always kept it well tuned and the oil changed very regularly. I think that helps a lot. I don't know if his was above average or not for a 302. I also don't know the ratio in the rear end, but it was stock. I know it couldn't have been too low; he got drunk one night years ago and proved to a guy that it would do 100 mph in 2nd gear. It amazed me that he didnt blow it up then. It probably contributed to the need for a new engine some years later though. Good luck with getting 20 out of a 390; I hope you can do it.

 

You could prob go with some 5W30 oil while you're at it, truck show on tv the other day gained a small rear wheel hp boost by changing ALL of the fluids to an aftermarket juice. Royal Purple, or Lucas if I remember right. I'm not too concerned about mileage, my right foot has an affliction of pushing itself to the floor once in awhile. Let 'er buck.

 

There ya go, oldeiron!!! I know my '71 doesn't cost me much when it is setting in the garage for the winter!!!! Only expense is the check to Grundy's once a year for the insurance. I like the new trucks too, but whenever I think half ways serious about getting one I remind myself what the $30,000 or more would build for a project truck!!!!! Friend of mine has an '05 F-250 Crew Cab, his monthly truck payment is more than my annual insurance payment!!!!!!

 

Don't know if it made any difference, but last oil change I used Mobile1. I had made a few short mixed use runs with the truck but mostly it sits with the high gas prices. I made a 300 mile trip yesterday and one fuel run I got 13.9 running around 75mph, 26-2800 rpms.

John

 

Hey Jo, I've been using Mobil 1 for years in my engines. At the time it was introduced to the market I was managing a Mobil station so I made a deal with our regional Mobil rep, and switched my brand spanking new 1978 Ford pickup over to it...... Stuck with it ever since, street applications as well as a number of racing engines. I can honestly say that I have never suffered an oil related engine failure in anything I was running the Mobil 1 in, and I do have a tendency to pound on my toys fairly hard from time to time. Just a bit of unsolicited testimonial for you.

 

That has to be good stuf, I just put M1 5-30 in the wifes 02 mustang for the first time and she actualy noticed a difference. Or has she finaly figgured out the program?

 

spjoegeoghegan deserves a serious answer, so let's look at it.

Weight requires power to move it, and the power in this case is gasonline. So clearly eliminating weight is a priority. Also friction is a huge factor. I am assuming this is a TRUCK so there is only so much weight you can remove and still have a truck.. Someone suggested a fiberglass tilt front end, but dollars to saving is always a factor too.. So you have to decide for yourself what you can get rid of for weight savings. (Who needs bumpers?)

But there are some things you can do to reduce friction. Go with some tall narrow tires and run them at the maximum air pressure. This will go a long way toward reducing rolling resistance as compared to the trendy gumballs that are popular. Semis are all about economy and they run proportionately narrow tires at near a hundred psi.
Also use the lightest lubricants allowable. 80w hypoid oil, 20w engine oil, etc.
Keep the windows closed and the air conditioner off.
Get the front end aligned at the best (not the cheapest,) shop you can find. Tell them you are going for economy. So go with the minimum toe-in and camber.

The 390 is known for it's drinking habit but you can ration it somewhat.
A camshaft with fairly high lift and short duration is in order. Valve overlap is an economy killer, especially at lower RPM.
Tri-Y headers. (That's two into one twice, then those two into one.) They are not popular because it's not what racers use, but big diameter long tube headers are strictly for very high RPM work. If you are going for torque and economy tri-Y is the only way to go. If nobody makes tri-Y headers for your engine, (they probably do though,) you want headers with fairly small diameter tubes. Make sure your entire exhaust is not restrictive but don't go for anything over 2.75" diameter dual pipes. Free flow mufflers that you can see through end to end.

For economy you will never want to see the high side of 4,000 rpm, maybe 3,500. So you don't really need a big four barrel carb. But there are some four barrels that can deliver very good milage. The Quadrajet comes to mind. [side note on that: lot's of guys bad mouth Q-jets because they take some figuring out and they are not easy to change the jets. But they are very reliable and extremely economical once they are set up.] The great thing about the Quadrajet is that they have very small primary venturis but great big secondaries. Economy is all about how you step on the loud pedal of course so if you can operate on those little primaries you are in good shape. But when you put the pedal down and those secondaries open up the power of that 390 will be revealed and your economy becomes a dream. (you might need to put a sponge under that gas pedal as a reminder.) But whatever carb you choose, go for the small primary large secondary formula.

Ignition: You need to use an ignition system that you can tune. There are several good systems to choose from. Just be sure it includes a very high voltage coil and maybe and MSD. Gap the spark plugs as wide as you can get away with.

If you are starting from scratch, the engine should be balanced. The combustion chambers should be matched exactly. All clearances should be at the outside limit except for the ring end gaps. Set it up loose for minimum friction. All ports should be carefully matched to the manifolds and polished. Choose the intake manifold from the many available for torque. Long small runners give you higher low end torque and better economy.

Obviously your differential gear should be high, 2.91 would probably be too high unless you are using very small diameter tires. But a 3.50 final drive would be good with tall tires.

Make sure your brakes don't drag.

When you get the engine put together you will want to have the carb jetted and your timing curve finalized on a dynomometer. This is critical. It's not cheap but it's the best money you will spend if you are serious about efficiency.

Install a big freaking vaccuum gauge on your dash and when you are driving, drive by the gauge. Keeping your vaccuum as high as possible will give you the best fuel economy.

Fill you gas tank at sun-up and do as much of you driving as you can when it is coolest.

Get rid of bug shields and outside mirrors and lumber racks and any camper shell that's bigger than your cab. A chin spoiler can help by reducing air turbulance under the vehicle.

I think you can surpass that goal, but it might seem like 'economy at any price.' However, you would have bragging rights like no other and the real bonus would be the thing would perform extremely well too.

 

Dear Friends,

Like most of you, I've been messing around with my '69 every since I got it a year ago, trying to get better mileage, all for a very noble purpose: so that I don't have to drive the Cavalier!

I've got a good gas mileage stock set-up, with the 240 I6 engine, although I just have the 3-on-the-tree, which is not overdrive.

I am not much of a mechanic yet (although I've learn MUCH over the past year!), so I have not messed with timing or with tweaking the carburetor, and definitely not with anything like exhaust or valves, etc.

Not to mention the fact that if you spend very much money at all on improvements to the engine, you will spend enough that you could have bought all the extra gas you needed to tool along at 12mpg for a long time!

But the one thing I have done that makes a WORLD of difference, that requires no mechanical skills, and that costs no money is to drive slower! I know this is the least fun answer, but it is also the most effective.

Here's why: I read an article some time back that was not about fuel economy, but was about top speed. The author said that the horsepower requirement to go faster gets higher the faster you go, and that the number gets higher at a higher rate. For example (these are imaginary numbers to illustrate the principle):

50 mph takes 100 hp
75 mph takes 150 hp
100 mph takes 250 hp
125 mph takes 450 hp

It has to do with drag from wind resistance. I am not well-read enough on the science of this to understand WHY it is like this, but I have since read more than one other article confirming this to be true.

For most non-aerodynamic cars like our trucks, the fuel economy tops out at about 50-55 mph, above which this increasing need for horsepower kicks in and sends the fuel economy numbers down the drain. (I understand that for more aerodynamic cars, the mph number is higher, and the mpg drops more slowly.) There's an over-simplified chart of this on fueleconomy.gov . On a states' rights basis, I do not agree with the national 55 mph speed limit from the 70s and 80s, but evidently it was the right number for fuel economy.

Like most of you, I do not enjoy watching the other cars go by, and I like to get where I'm going in good time, so for a while I didn't want to slow down. During the recent gas price spike, however, on the day I filled up for $2.93/gal, I got desperate and tried slowing down.

So, here are my results:

For my '89 Suburban, with the 350 engine and 4-speed overdrive automatic:
-at 70 mph, I was getting 12 mpg.
-at 60 mph I am getting 17 mpg.
-I haven't tried 55 yet.

For my '69 F100, with the 240 and 3-speed manual, no overdrive:
-at 70 mph, I was getting 14 mpg
-at 60 mph, I was getting 18 mpg
-at 55 mph, I am now getting 22 mpg!

Your results may vary, or you may "feel the need, the need for speed" more than you feel the need for economy. I estimate, though, that slowing down on the highway from 70 to 55 will give you a 50% increase in fuel economy.

Here are some psychological factors that may help:
-calculate how much you are getting paid for driving your truck (the very thing we love to do) a little longer. 75 minutes driving instead of 60 minutes in order to get 18 mpg instead of 12 mpg, at $2.25/gal will save you about $3.50. That means you're getting paid $14/hour to drive your truck a little slower. Talk about beating the system!
-think about how many more people can see your truck if you are driving 55 mph and they are all passing you. They get a good look at the rear end, and that beautiful FORD on the back, then they get a good look at the bed, then the cab, then the hood, then a good look at the grille in the mirror. It could make people so happy seeing a "Restored Ford" that they don't go commit crimes or suicide or get a divorce like they were planning. They might see the love of Jesus shining through the love you have put into your truck, get saved, and go to heaven! (Perhaps that is a stretch.)

For me, 20 mpg is the imaginary line. If I can keep her cruising above 20 mpg, I feel justified in using her for a daily driver. So, I'll just keep tooling along at 55, and keep calculating mileage in my little notebook, and keep looking like a man in my '69, instead of looking like a girl in the Cavalier!

P.S. Is there any way to convince my wife that she could do all her driving in the Suburban? Right now we only use it when we're ALL going somewhere. If she'd go 55, and get 20 mpg, I could sell the 2003 Cavalier for $5-6,000, save the insurance money each month, and even considering extra gas expense, still come out fine. Then the $5,000 could go for all the stuff I still need/want to fix on the two trucks. Anybody had any luck with this kind of wife-convincing project?

P.S. I finally dug into the wiring this week, and got all lights working properly! (No promises that all the wiring is still like it was when new, but it all works!)

 

Sacred69, your post was the perfect caveat to all that which I posted above. But I, being an old guy, have learned that everyone is going to drive just the way they need to at any given time. Did you notice the part about the vaccuum gauge on the dash? If they actually did that, and I doubt that they will, it would be following your suggestion and going beyond it.

 

Bdox and Sacred69, the two of you have provided some very good insight and information for everyone. Hopefully spjoegeoghegan got the information he was looking for. I enjoyed reading both posts and learned something from both of them. Thanks, John.

 

I reacently bought a 2006 Scion XA. This car is made by Toyota. It has a 1.5 liter with a 5 speed. It gets great mpg; "but" I have found even with it that there is a noticable difference in mpg according to speed. It seems to come down to RPM's. This car gets aroung 35mpg driving an average of 60-65 mph. It is turning around 3200 RPM's at this speed. It gets 30-31 mpg driving at 70-75 mph when it is turning around 3700-3800 RPM's. This car should have had 5th gear as an overdrive, but it isn't. Probably because the 1.5 mouse's couldn't move it if it was OD. I'm sure you are all laughing by now at the idea of driving a Scion XA. I didn't think I would like it untill I drove it. I was very surprised. But anyway, what you guys are saying about gas mileage is true no matter what the vehichle is. Merry Christmas

 

i put a late model 5.0 in my 69 with an aod and 3.50 gears. i get 19mpg on a regular basis and have gotten as good as 21 on a trip. you'll need more gear if you drive in hilly area which will also decrease mileage. i have 62 ranchero with 5.0 and 5 speed and 3.0 gear that gets 30mpg. but it weighs 2600 and does'nt have flat front.