390 fe gas mileage [Archive] - FSB Forums

: 390 fe gas mileage


79broncoowner
10-17-2011, 07:59 PM
I have a 390 in my 79 bronco. I get 8 miles per gallon maybe 9 on a good day but no better. I have been told that it should get 12-13. I have my timing set correct, I have a 600 edlebrock carb with headers and an rv cam. The vacuum advance is hook up and working right. No brakes dragging. I have 33 inch tires with 3.50 gears and my speedometer is correct. Any idea on how to improve the mileage. Also I have tried different grades of gas and it does best on 87 octane.:banghead

Saltlife
10-17-2011, 08:05 PM
Search around and you will find your answer. Also what trans do you have?

79broncoowner
10-17-2011, 08:36 PM
I have a 4speed. I have searched everywhere. Though maybe someone had a 390 that got better mileage that could help

Pedestrian
10-17-2011, 08:51 PM
My 400 never got better than 11 so I find it difficult to believe a 390 would be any better.
None of the FE engined trucks I have owned ever got better than 14 and that was a half ton 2wd

impalaslayer
10-17-2011, 08:51 PM
my 360 wouldnt get much better then that. id still take it over the modifieds that came in the broncos though

abrojal
10-17-2011, 08:58 PM
I have a 4speed. I have searched everywhere. Though maybe someone had a 390 that got better mileage that could help

but what about the compresion of that 390.

A1Fiddler
10-17-2011, 09:48 PM
Lot of good info here:

http://fullsizebronco.com/forum/showthread.php?t=114950

Alvin in AZ
10-18-2011, 01:31 AM
I have a 390 in my 79 bronco.
I get 8 miles per gallon maybe 9 on a good day but no better.
I have been told that it should get 12-13.

Sounds right on the money to me, and in my experience...
that's what you should be getting, easy.

I get >12mpg on my '75 F150
360FE+T18 -original- 2100 carburetor
3.50 gear, 31.5" 235/85-16E's
Comp 252/252 straight up
Stock manifolds, opened-up stock Y-pipe
Straight through 2+1/2" muffler and pipe
...and about 95k on the rebuild too!
Over 13mpg when it was first rebuilt. :)

My son is getting 12 to 13 mpg on a rebuilt 360FE
Unknown cam and miles!
We call it "The Farm Truck" it has a flat bed and really was a farm truck.
It was given to me by a cowboy buddy for scrap and parts. :)
Stock manifolds with dual exhaust.
It pulls stronger than mine is all we know about the engine.
'75 F250 360FE+T18 stock 2100 carburetor
3.73 gear 235/85-16E's

His -was- getting 8 to 9mpg before we rebuilt the 2100 carburetor
using -used- parts I had on hand. :)

It was a blown power valve messing up his mileage I believe..

The trick to good gas mileage is in the carburetor adjustment IME.
You know how to do that? :)


timing set correct,
600 edlebrock
headers
rv cam
vacuum advance is hook up and working right.
No brakes dragging.
33 inch tires with 3.50 gears
my speedometer is correct.
it does best on 87 octane.
Since there is for sure something wrong with it, then
-at least- one of those things in that list is a wrong.

Start over on your list of things "that are right"...
1) What's the actual timing?
a) At idle?
b) Full mechanical at what rpm?
c) Mechanical plus vacuum advance at what rpm?

2) Carter AFB? ;)
a) Who adjusted it?

3) "RV cam" covers a lot of ground.
a) Which cam is it -exactly-?
b) Is it timed straight up or retarded?

4) Cool that your speedometer is right. ;)
a) What about the stinkin' odometer tho... Is it right? ;)

5) It's cool to hear it's running good on 87 octane. :)
...and for-sure, it ain't pinging -any-? ;)

Alvin in AZ

79broncoowner
10-18-2011, 07:50 AM
No pinging and I had all the timing readings a while back but can remember where I put them. I tuned the carb with a vacuum gauge. I also tried to go with smaller jets but it was running way to lean so I put the stock jets back in the edelbrock. I think at idle the timing is set at 12 degrees. I have also put a new dist. in not long ago. The compression is good also. The engine has about 70000 miles on a professional rebuild. It is bored 60 over also.

Robs79BBbronco
10-18-2011, 09:00 AM
the 360/390's were gradually phased out in favor of the 429/460's.....the FE's were heavier and not as efficient.they are good motors, but not as good as the 385 series.:goodfinge

BigWheelz
10-18-2011, 09:28 AM
Assuming a good tune and an engine in good condition, it is probably your driving style. Do not expect 12 mpg unless you are spending the majority of your time driving on the highway.

UTfball
10-18-2011, 10:27 AM
Assuming a good tune and an engine in good condition, it is probably your driving style. Do not expect 12 mpg unless you are spending the majority of your time driving on the highway.


This is what I'm thinking. You'd top out at 12mpg's if you only drove hwy miles. That aside, you said your speedo was correct...so you swapped the driven gear in the t-case? If not, with the larger tires and stock gear ratio...your speedo/odo aren't correct.

78Bronko
10-18-2011, 02:53 PM
I don't even count MPG in my 460; is really even worth it? I just fill her up when she is thirsty. I can't imagine the 390 doing better than 12 unless you were pushing it down the road.

Alvin in AZ
10-18-2011, 03:10 PM
I don't even count MPG in my 460; is really even worth it?
Yes because changes can be detected with that information,
like a blown power valve in the carburetor for example.

---------------------

OP,
Don't listen to the naysayers, there's something wrong with
your engine or figures or something. Many guys get used to
bad mileage and just accept it and take it lying down. ;) You
can do that too or get to the bottom of what's going on with
your rig by digging into it like you mean business.

Your call. ;)

Just don't whine at me about your FE getting less than 11mpg
in a light weight Bronco.

If it's a "not running right" problem then after you get it running
right it'll have more power. At that point don't brag on it here
-too- much because not everyone can own an FE. ;)

Alvin in AZ

78Bronko
10-18-2011, 03:25 PM
[QUOTE=Alvin in AZ;2731596]Yes because changes can be detected with that information,
like a blown power valve in the carburetor for example.[QUOTE]

---------------------


I would THINK one would notice a bad powervalve; especially if everything else is "correct" as the OP stated. What we Don't know is the age, milage, and condition of the engine, which obviously was not original. Too many variables not known. a simple carb rebuild is the first place to start, set timing AFTER a carb rebuild, then try try try again. The 600 edelbrock should be a good carb for that engine, I wish I had one on my 460 :(

Robs79BBbronco
10-18-2011, 05:15 PM
Just don't whine at me about your FE getting less than 11mpg
in a light weight Bronco.


light weight?:histericait's a '79

79broncoowner
10-18-2011, 06:29 PM
I have owned this bronco for about 10 years. I had the engine rebuild by a machine shop. I know everything about this bronco. No one works on it but me I know every bolt and nut. I have drove this bronco many ways trying to get better mileage I would be thrilled to get 11 I never have. All I know is several people on different fourms have said that a 390 would get around 11 or 12 miles per gallon. My speedometer is very close. I have 3.50 gears with 33 inch tires and use a 16 tooth speedometer gear in the transfer. Also I would put my 390 up against any 460 any day. I had a truck 2wd with a 460 auto wasent impressed.

Ziggy
10-18-2011, 10:01 PM
Running 3.50 gears on 33's doesn't help much either unless you do nothing but highway driving. I run 4.10's on 33's and get about 11-12 with a 351M at 70 MPH. If I run at 55-60, my MPG goes up as well which should be true of any vehicle. You have to remember that from the mid 70's to the late 80's, the national speed limit was 55 MPH so that is where you'll get your best MPG.

Alvin in AZ
10-19-2011, 02:51 AM
I have owned this bronco for about 10 years. I had the engine rebuild by a
machine shop. I know everything about this bronco. No one works on it but
me I know every bolt and nut. I have drove this bronco many ways trying
to get better mileage I would be thrilled to get 11 I never have. All I know is
several people on different forums have said that a 390 would get around
11 or 12 miles per gallon.

Cool and x2 on all that! :)

So what cam did you pick for the engine when it was rebuilt?
(brand, type and size and was it timed "straight up"?)


My speedometer is very close.
So what? :/

You don't use the speedometer to check mileage. ;)
How close to "right" is your odometer?
Have you ever bothered to measured it? ;)
Answer the questions in post #8.

Alvin in AZ

Alvin in AZ
10-19-2011, 03:05 AM
light weight? a '79
Hmmm... yeah... I guess it isn't really any lighter than an empty pickup bed huh? :)

Alvin in AZ

Alvin in AZ
10-19-2011, 03:39 AM
the 360/390's were gradually phased out in favor of the 429/460's...
the FE's were heavier and not as efficient.they are good motors, but
not as good as the 385 series.
385's sure enough have good flowing heads I hear. :)

BTW, this '75 Ford F150 weight table shows 460's are 100 pounds
more than a 390...
http://www.panix.com/~alvinj/file12/weights.jpg
That table's for my '75 F150 which doesn't show the 302 since it
wasn't offered in the F150 the first year. In the other weight tables
they show the 302 weighs less than a 300-i6.

But how do you figure the "phase" part? ...351M's and 400's were
the replacements for the more expensive to make FE engines.

Careful running down FE's because they are related to the FT's. ;)

Us FE/FT owners are trying to "play nice" and not gloat too much,
so don't be making brash statements. ;)

Alvin in AZ

79broncoowner
10-19-2011, 07:45 AM
Yeah My odometer is right on the money. It matches the 98 ford truck odometer my wife drives. As far as the cam the machine shop owner asked me if I wanted an rv cam he said it would help the preformance and gas mileage.That is all I know about it. Thanks for all the response.

Robs79BBbronco
10-19-2011, 08:25 AM
Careful running down FE's because they are related to the FT's. ;)

Us FE/FT owners are trying to "play nice" and not gloat too much,
so don't be making brash statements. ;)

Alvin in AZ
i'm not running them down, or knocking them......good motors indeed, but not known for getting "good" mileage and let's face it....no matter the motor in the OP's bronco, he's not going to get much better than that anyways.
79broncoowner can put your 390 up against my 460 any day, but i won't have to stop for gas as often:goodfinge

Alvin in AZ
10-19-2011, 03:38 PM
79broncoowner can put your 390 up against my 460 any day,
but i won't have to stop for gas as often
Cool. So, you got an added gas tank in your rig too, huh? :)
(going to do that pretty soon, got the parts gathered)

460 gets better gas mileage than an FE? 8-/
Who's been blowing smoke up your butt? ;)

The OP's tires etc isn't helping like Ziggy said but 8 to 9mpg?
Some thing's wrong and the OP strikes me (so far) as not
really wanting to get "technical" about it, just wants to bitch?
I'll back pedal my ass off (on all that) as soon as he starts
getting specific with the information exchange. ;)

Alvin in AZ
ps- You know both 460's and FE's got screwed with the 4
degree cam timing retard for NOx emissions business. Cheap
and easy to fix that tho, more power-and-better gas mileage.
BTDT with my '91 351w even! Yep, went up -at-least- 1mpg.
I'm not bragging just a fact. Don't forget the improved power
band that went with that 1mpg, that made it worth it all by
itself.

Robs79BBbronco
10-19-2011, 04:51 PM
Alvin in AZ
ps- You know both 460's and FE's got screwed with the 4
degree cam timing retard for NOx emissions business. Cheap
and easy to fix that tho, more power-and-better gas mileage.
BTDT with my '91 351w even! Yep, went up -at-least- 1mpg.
I'm not bragging just a fact. Don't forget the improved power
band that went with that 1mpg, that made it worth it all by
itself.

x2......def. makes a difference:thumbup

wyoranch
10-19-2011, 05:37 PM
Cool and x2 on all that! :)

So what cam did you pick for the engine when it was rebuilt?
(brand, type and size and was it timed "straight up"?)


So what? :/

You don't use the speedometer to check mileage. ;)
How close to "right" is your odometer?
Have you ever bothered to measured it? ;)
Answer the questions in post #8.

Alvin in AZ

Ummm..... If your speedo is right then your odometer will be. The cable that runs your speedo runs the odometer also....

4drbronko
10-19-2011, 05:46 PM
I get 13.5 outta my FE, granted it's 1/2 the weight of a Bronco, but it's also running 2 600cfm carbs.

Alvin in AZ
10-19-2011, 06:02 PM
Ummm..... If your speedo is right then your odometer will be.
The cable that runs your speedo runs the odometer also....
Yeah, but, nope. :) Believe it? :)

The speedometer is not directly geared like the odometer is.
I've adjusted speedometers so they read closer to right and
that adjustment had no effect on the odometer.

The speedometer is driven by a spinning magnet effecting a
steel cap (or the other way around). That force is pushing
against a spiral spring than can be adjust like a volt meter.

Cool huh? :)

-----------------------

I'm hoping the OP is real busy and not just lazy;) ...so later
we can get to the bottom of what's causing his 8 to 9 mpg
"results" real or imagined (like the odometer is off).

It'll be cool. :)
But we can't do it without 'im. ;)

Alvin in AZ

79broncoowner
10-19-2011, 07:38 PM
LOL good one about not stopping for gas as often. What does your 460 get anyway? I am not burning any gas this week anyway I have the transmission and tranfer case in the floor and replacing all the gaskets in them. The transmission was leaking out the front and got on my clutch and it started jumping real bad. So I have a new flywheel ordered as well as a new clutch and all the gaskets. Cant wait to get it back on the road. This week I am driving my 74 one ton flatbed it also has a 390 with a lumpy cam and all the goodies. I have never check the mileage on it whats the use. I use it to pull my tractor and haul wood. I love this truck almost as much as my 79 bronco

newageroman
10-19-2011, 08:19 PM
you can check the odo against some mile markers on the hwy. one mile might not be accurate, but 10 should. Then use the difference (if any) to adjust your mileage formula.

slw210
10-20-2011, 02:42 PM
Use a GPS or the mile markers to check your odometer, another truck is a poor way to check an odometer.

First off, let use know where you live. It matters for fuel mileage. How closely are you getting your gas amounts? Are you driving only in town 6 miles one way at rush hour and a trafflic signal every 1/4 mile?

I do not believe I ever got better then 5 or 6 MPG with an FE Ford, I just have to push the go pedal all the way. Course I was a teenager, back then. That was a great motor for a truck. Ah the good ole days.

I agree with the gearing, as mentioned even the original gearing was made for 55MPH to get best MPG Highway and that was in a lighter truck.

RV is a pretty poor way to describe a cam, I wouldn't let anyone touch my vehicle if they said they were going to put a RV cam in it.

Now you gone and made me want a mid-70s Pick-up.

Robs79BBbronco
10-20-2011, 04:01 PM
LOL good one about not stopping for gas as often. What does your 460 get anyway?

10 or 11 if i'm lucky:rolleyes:mine sounds a lot like yours, 600 edelbrock,4 speed, 33" tires, etc.....stock everything else

Alvin in AZ
10-20-2011, 04:22 PM
I do not believe I ever got better then 5 or 6 MPG with
an FE Ford, I just have to push the go pedal all the way.

RV is a pretty poor way to describe a cam, I wouldn't let
anyone touch my vehicle if they said they were going to
put a RV cam in it.

Now you gone and made me want a mid-70s Pick-up.
Cool! LOL :)
Do it! :)
Get a Bump-side even? ;)

I got 7+1/2mpg with an FT engine in the biggest U-Haul
they made and yep, had the pedal to the floor the whole
time ...which of course makes the mixture richer through
the carburetor's "full power circuit".

------------------------------

From the late 70's when I first got 235/85-16's to 2006
I had to add 12.8% to the gas mileage because the '75
F150's odometer was off that much. In 2006 went from
3.25 to 3.50 gears and now it's only off ~4.6% but the
speedometer is right on the money up around 60mph! :)
(I'd adjusted it before and by-chance turned out perfect)

The swap from H78-15 tires to 235/85-16's with a 3.25
gear... put the whole rig so-far-out-of-design-range there
was no replacement speedometer gears that could fix it
without an aftermarket gear box. So I decided way back
to not change the speedometer gearing ever, and so, at
least I've had -consistency- all these years. LOL :)

With the 3.50 gearing I could swap the driven gear that'd
put the odometer right on the money ...but ain't gonna.

http://www.panix.com/~alvinj/file12/Fdrive018.jpg
http://www.panix.com/~alvinj/file12/Ford9inch.jpg
http://www.panix.com/~alvinj/file12/gearshift1.jpg

http://www.panix.com/~alvinj/file12/choke1.jpg
...nothing wrong with a gasoline wastin' choke a hacksaw,
hoof rasp and a shotgun shot-size-collection can't fix! ;)

Me and my son just got done doing that to the '75 F250
Farm Truck's 2100. That and the-rebuild went from 8 to
9mpg like the OP to 12 to 13mpg with just a carburetor
rebuild using -used- parts but the rebuild included a power
valve that wasn't punctured like the old one was.

It controls the full power circuit! ...and so, -will- give you
mileage similar to what I got with the mid 70's U-Haul,
see it?

(FT's outlived FE's in production partly due to U-Haul)

A backfire through the carburetor can puncture one of
those sorry things the-first-minute after first-firing-up a
newly rebuilt carburetor! If you've -ever- had a backfire
through the carburetor and you don't think you need to
check your gas mileage at least ever'once in a while...
then you -deserve- the bad mileage.

"you get what you deserve and deserve what you get"
-my grandpa that was orphaned so early he couldn't
remember his mom

I can type my stupid stories out on the internet (until the
dead cow from having calving trouble comes home even;)
about how to go about fixing bad gas mileage but -you're-
the one that's got to get off your lazy butt and actually do
something about it.

First thing you gotta do tho is... stop ASSuming shit!

The Bastard in AZ

Alvin in AZ
10-20-2011, 04:24 PM
10 or 11 if i'm lucky mine sounds a lot like yours, 600 edelbrock,
4 speed, 33" tires, etc.....stock everything else
x2! :)

Alvin in AZ

ValentineWYO
10-23-2011, 06:23 PM
Pretty much if you want better mileage than your getting you should put a 302 in there. The 390 is great for passing everything but a gas station. I put one in my 75 f250 to replace a blown 300 and have been bi-polar from the performance vs gas money ever since. Just drive it and love it and buy a geo for a daily driver if you need to.

Alvin in AZ
10-23-2011, 09:15 PM
Pretty much if you want better mileage than your getting you should put a
302 in there. The 390 is great for passing everything but a gas station. I put
one in my 75 f250 to replace a blown 300 and have been bi-polar from the
performance vs gas money ever since. Just drive it and love it and buy a geo
for a daily driver if you need to.
Not x2. :)

There's something wrong with the 390 or what's installed on it or what it's
installed in. Even if you get a Geo, fix the 390's situation anyway. Bet you'll
get a better running engine (more power) in the process.

Butthead in AZ

dagamore
10-24-2011, 08:00 AM
only problem with going to a 302 for mpg, is that it might not be enough motor, that missing tq will make you run the motor with more throttle. I know i would.

Shaker666
10-25-2011, 03:18 AM
Nothing 5 psi of boost couldn't solve if you really wanted to run a SB Ford. The real issue is the bellhousing bolt pattern. You're stuck with the big block bolt pattern if you intend to keep your stock transmission or want to break the bank with some kind of ridiculous bellhousing adapter.

My donkey gets about 10-12 mpg and that's the stock 400M (rebuit), stock C6, stock NP205 t-case, and 4.11:1 gears on 35" rubber. I live at about 2500 ft.

I run full synthetic fluid in the axles, transmission, t-case, and engine. The engine itself is stock except for long tube headers into a Y-pipe, Crane Cams flat tappet cam emphasizing low end torque, double roller timing chain installed straight up, and a 351W GT-40 intake adapted to the 400 for fuel injection. It is running sequential injection (via 30# injectors) and the waste spark EDIS8, so no distributor anymore. 65mm throttle body and 70mm MAF.

dagamore
10-25-2011, 05:40 AM
Shaker666

5psi of boost with fix most issues, say with a single t3/t4, hell two of them its for a V8 not a I4!

79broncoowner
10-26-2011, 07:46 AM
Ok here is my timing readings at different rpms. idle is 11 degrees 1000 rpms is 20 degrees 1500 is 29 degrees 2000 is 32 degrees 2500 is 32 degrees and 3000 is 36 degrees. Vacuum is 15 at idle Does this sound about right? The dist. is a rebuilt unit stock to the engine.

79broncoowner
10-29-2011, 03:46 PM
HELLO any body there.

slw210
10-31-2011, 02:46 PM
15in sounds low, you may be running lean or need to advance the timing or both. See THIS (http://www.secondchancegarage.com/public/186.cfm)

Alvin in AZ
10-31-2011, 04:29 PM
15in sounds low...
See THIS (http://www.secondchancegarage.com/public/186.cfm) <--{that ;}

Cool. :)

I just now learned this and always wondered if my elevation effected
my vacuum readings at idle...

"Note: The following readings will be typical at sea level. In general,
subtract one inch for each 1000 feet above sea level."

Alvin in AZ

79broncoowner
10-31-2011, 08:17 PM
Thanks for the information I will check the link out.

79broncoowner
10-31-2011, 08:18 PM
That was some great information I cant wait to plug the vacuum gauge back in. Thank so much this should be very helpful

79broncoowner
07-14-2013, 05:37 PM
Now the old bronco is down to 4-5 miles per gallon pulling my camper. It was 7-8 pulling the camper. My spark advance was stuck so I fixed that but it is still in the 4-5 range. I am thinking about selling out and getting something newer. I know it wont pull like the 390 but I am sick of the terrible mileage. Oh yeah my ac is leaking AGAIN. It is a dealer installed unit works great around town but on a trip something always goes wrong with it and my new axle that came preassembled with the bearing and seal is also leaking. I have just about had it.

InfoFord
07-14-2013, 06:34 PM
Now the old bronco is down to 4-5 miles per gallon pulling my camper. It was 7-8 pulling the camper. My spark advance was stuck so I fixed that but it is still in the 4-5 range. I am thinking about selling out and getting something newer. I know it wont pull like the 390 but I am sick of the terrible mileage. Oh yeah my ac is leaking AGAIN. It is a dealer installed unit works great around town but on a trip something always goes wrong with it and my new axle that came preassembled with the bearing and seal is also leaking. I have just about had it.

with blended fuel your mileage will suffer regardless of vehicle new or old

if your advance was stuck a good chance your power valve is blown

check the vent tube on the axle and make sure it is not plugged

79broncoowner
07-14-2013, 08:49 PM
Thanks What is a good way to check the power valve? I will also check the vent tube.

66CC
07-15-2013, 09:04 PM
Do you have a fan clutch?
A bad one will drop your mpg.

If I remember right, Edelbrock carbs don't have powervalves.
They have those needle things like rochesters.

I get around 8 w/ a 75 f250, 4.10, 390,c6. It has a good cam for pulling, that might be the problem. You may have to upgrade to a cam for more mpg.

79broncoowner
07-15-2013, 10:22 PM
I really don't think edelbrock has a power valve either and when I had the engine built several years the guy put an rv cam in it( I don't know the lift or anything) but he said it would help the mpgs. I don't know what the problem is but I need to get it fixed. The fan clutch is new.