Gas mileage?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I have a 400 in a '73 Galaxie that gets about 5 mpg, like you. However, it has a pretty badly burnt exhaust valve. You should have heard the air hissing out of the tailpipe during the leakdown test.
Elder User
Joined: Jul 2005
Posts: 969
Likes: 1
From: North Texas
Originally Posted by BigBody
I know most people seem to say the 400 should get atleast around 12 mpg. In my 1977 F-150 4x4 I have only been getting 5 to 6 mpg. I have 33 inch tires on stock gears
The 4x4 will drop your gas mileage. Bigger tires should drop your gas mileage. Stock cams are retarded and will hurt your gas mileage.
If you lose more than 2mpg from regular you have a problem. When my mustang drops 1.5 mpg it wants the spark plugs and points cleaned up. When it dropped 5mpg I had a fuel leak.
Tuned
Joined: Sep 2003
Posts: 348
Likes: 2
From: Northern Michigan
I've heard about compression
Originally Posted by roger dowty
compression is the only savior imo. if the bottom end is tight save for some aussie 2v heads.
I've got a 307 Chev that runs like a top and it needs a home. I get about 9 mpg with a 360 Dodge, and about 11 with a 350 Chev in trucks that always weigh 8,000#or better. 12 in an empty truck would break my heart. An FI 300 would be sweet but thats not going to happen.
Has anyone put aussie heads on an otherwise stock 351M (1979)? What could you expect?
Last edited by palmrose2; Aug 25, 2006 at 06:29 AM. Reason: forgot to mention something
Post Fiend
Joined: Jan 2003
Posts: 10,323
Likes: 2
From: Montana Territory
Its not a matter of slapping the aussie heads on a 351M/400.... the motor really has to be built around it... 70,000 miles is quite a while, 70% of its life is gone at that mileage. Modern engines go a lot longer between overhauls, but these engines were really designed to make it to 100K and thats about it.
Laughing Gas
Joined: Mar 2006
Posts: 1,164
Likes: 2
From: Tri-Cities, TN
I get 13.5 with my '79 F150 4x4/400/T18/3.50. 31x10.5 tires, usually driving rural highway at 62-67 mph. I think I can do better with a slightly larger tire that is narrower (33x9.5) as I turn around 2500 rpm at cruise, which is way too fast for this motor, and a fan clutch. Also, an under bumper airdam from a late 80's truck will fit pretty good and reduce drag a little without hurting approach angles much.
Posting Guru
Joined: Mar 2005
Posts: 2,068
Likes: 0
From: western montana
most claim better economy with a 400 over a 351. You will certainly get more power- with the right build you will get over 300hp/ 420ft lbs and get better mileage than any 351m you could build.
Like matts72 said- you need a tight bottom end for the increased compression of the aussie heads.
Like matts72 said- you need a tight bottom end for the increased compression of the aussie heads.
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Junior User
Joined: Dec 2004
Posts: 57
Likes: 0
From: Subiaco, AR
my lifted 78 Bronco get 10-12mpg period. The two major road trips Ive taken & all the putt-putting around town it gets the same, loaded or stripped down. Now low range I have no clue since the driver upgrades to alky injection. 
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