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Bocephus 12-28-2001 03:29 PM

78-79 bronco milage
I know this is a dumb question,but what kind of milage can these get with healthy running 351-400 modified.My guess is 8-9.I had a 78 ramcharger with a slightly tweeked 360 that got 9 in town,it was full time 4x4.

Now hold it,,I think its time to take this baby for a spin,Lets lock in the hubs so I can put on a big Ol GRIN!

MY2ND78 12-28-2001 06:27 PM

Re: 78-79 bronco milage
Guys claim to get up to 12MPG. Some rare cases claim up to 19, but we're finding it hard to believe. Go to and do a search on "MPG"

The trouble with being on top...You always have to look over your shoulder. The best never rest. Fear the FORD thunder!!!

Sixlitre 12-28-2001 11:00 PM

Re: 78-79 bronco milage
You won't be pullin' down 19 with those motors

The 351 and 400 Ms were heavy, thirsty devils with very little relation to the smallblock 351 Windsor and it's fuel concious cousin, the 302. True the Ms can be built to deliver a pile of power and torque, they never came with fuel injection or O.D. automatics and non-lock up C-6's weren't known for delivering the best mileage (just rock solid dependability and handling gobs of power).

If you could take the pain at the pumps a 360 equipped Ramcharger with fulltime 4WD can dish out, you won't be getting any worse from an M engined Bronco(maybe slightly better).

Lately in all the cold weather and the 85mph rips into the city, my EFI 302 is down around 13mpg. In the Summer after a few ignition mods I had been posting 19 mpg combined.


**DONOTDELETE** 12-29-2001 12:34 AM

Re: 78-79 bronco milage
fwiw - I get 14.5mpg on the highway, corrected for tires/gearing, with a 351M, Edelbrock Performer, Holley 600, Dynomax Headers and 2-1/2" duals thru glasspacks, no cats and an open air cleaner. Pretty standard setup, with no vacuum advance and timing at 10 deg BTDC, and 93 octane gas. truck is lifted 2-1/2" with 35's and stock gears. It's easy to get road numbers below 10mpg with a heavy foot, and it gets 5-6mpg on the beach.

'79 Bronco
'89 Trooper

Sixlitre 12-29-2001 10:55 PM

Re: 78-79 bronco milage

That's pretty dern good for a truck set up like that. I take it you're staying under 85mph on those hwy trips.

You're cutting yourself out of a couple of mpgs with no vacuum advance. I'm new to Fords, but I run serious vacuum advance on my 360 4bbl Mopar street car and it made a 3-5 mpg difference with zero loss of acceleration. In fact, if anything, it improved part throttle acceleration.

The Mopar sits at 12 degrees initial, spins out another 20 degrees mechanical by 2600rpms taking it to 32 degrees total mechanical advance. After that I add in another 23 degrees vacuum advance taking it to 55 total (mech and vac) degrees(all in by 2600rpms).

This worked before and after I installed my MSD-5, Blaster coil and plugs gapped out to .055. Give it a try, before OPEC turns it up again.


**DONOTDELETE** 12-31-2001 01:48 AM

Re: 78-79 bronco milage
yeah, I keep a pretty low profile on the highway runs, a lot of small towns and two-lanes to and from the beach.
I ran the vac advance and played with timing until I was blue in the face trying to eliminate low-load spark knock for a long time after installing the intake/carb/headers. Tried retarded combos back to almost 0-deg adv, and it would barely start, advanced beyond 10 deg, port and manifold vacuum....every combo I could think of, and finally found by accident, after resetting the timing back to stock 10deg BTDC, and taking it for a test drive, and not realizing that I had left the vac hose off and plugged with a golf tee....that it ran better than every combo I had tried. Plugs are Bosch gapped to stock 044 - I had run manifold vacuum up to 44 deg total advance with 050 gap as one of the combos (38 deg total adv is recommended max for this motor), and it ran like crap. Bottom line, with the intake/carb setup listed, 10deg adv, 044 gap, stock ignition/coil, Bosch Platinums and an open air cleaner (no smog), it has been "set-it-and-forget-it" for four years with regular tuneups, great off the line, good midrange acceleration, no spark knock under light or heavy load. Don't ask me why - I'm no motor expert, just lucky I guess.

'79 Bronco
'89 Trooper

**DONOTDELETE** 12-31-2001 10:43 AM

Re: 78-79 bronco milage
My 77 F150 2wd with a 400m would get nearly 15 on the interstate. It got a solid 12 or so everyday around town and 12 towing a car or boat down the road. It had a 2.75 axle, and just used torque to pull with. It seemed to have unending amounts of torque, and would probably pull up a boatramp in high gear at idle if you asked it to.

My 82 351w 4v Bronco, with no OD and 3.50 gears gets 10 at best every day, 12 on 55 mph trips, and as low as 8 towing at 70.

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