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Supreme Being
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| Not a Y question but still a Ford. I just bought a '79 Bronco (351M w/ C6) for hauling things and bad weather days. My understanding is that it is going to be a gas HOG (8-10mpg). I get about 18-20 with my 312 and fordo/fmx in my 4dr 500. Is the Y just that more efficient. Is there any ways to improve the 351? My guess is the fairlane is about twice the size of the bronco. I haven't checked the rear diff on the bronco, but I think they came with 3.50 gears. I still need to tune the carb because it idles really rough but I don't think that will make much difference on the road. Anyone using a C6, is there an overdrive? Any suggestions appreciated! - John
John: Lake Forest, IL
'57 Fairlane 500 - Looking better every day.
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Supreme Being
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There's 3 big reasons the Bronco is going to use twice as much gas as your car.The 4 wheel drive.Lots of additional friction,even when in 2 wheel mode. .The 351M and 400 engines were great as far as HP but they were always gas hogs.And the Bronco outweighs your 57 by about a 1,000 pounds.
 
Paul, Boonville,MO
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Supreme Being
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It is probably to blame on the whole package rather than the 351M itself. The C6 is a gas hog. It probably has shorter gearing than a car. It's a truck engine with lower compression which reduces efficiency. The 12.5% increase in displacement doesn't help.
For better mileage, drop in a Y Block.
Lawrenceville, GA
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Supreme Being
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I worked for Ford when the 351M/400 came out and it was in the trucks as well as passenger cars. When the 460 was dropped from the Lincoln line the owners who now were poking around in a 351M/400 with the same or worse mileage, were seriously pissed. A low compression, low horsepower emission engine. 165 Horsepower only offered with 2bbl carbs. The early ones ate up valve guides in about 30k miles. You could hear them clicking at idle. Ford's idea was big block torque and small block gas mileage, they got the opposite. Gas hog no matter how you slice it. Broader Performance makes a "wide ratio" C6 with a higher 3rd gear. I have one in my 66 F100 390.
57 Black Tbird 312/auto
65 Galaxie 500 2drhdtp 352/Cruiso
66 F100 Custom Cab ShortyStyleside 390/C6
Monterey Bay, California
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Supreme Being
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Big Broncos were all gas hogs. One thing you can do to help out the performance is what I did to my 79 Ranchero w/351M. Pick up a timing chain set-up from Summit w/ the adjustable 3-way crank gear. It has keyways in it where you can advance the cam timing 2 or 4degs. Helped out my Ranchero. "Someone said" that in order to pass emissions they had to retard the cam a couple degs. Who knows. I advanced mine 2degs (wish I would have gone 4) and it starts and runs great.
Dan Gregory Mi. 48137
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Supreme Being
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| I bought a 1978 Bronco new with the 351 and C-6. Best mileage was 14-16 highway. Drove it for 20 years! Best thing I ever did for it was have heads rebuilt and put in Comp RV cam. I always remember that truck. Bought it the same week all the stations rationed gas because of the "shortage". That was when gas prices started their climb.
Ol'ford nutCentral Iowa 56 Vic w/292 & 4 spd.
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Supreme Being
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| thanks guys! I know the engine was rebuilt about 7 years ago: got a powermax hydraulic cam and "australian heads" among other things. We'll see how she runs after a little tune. So basically what you're telling me is that it was not a great motor series and long term a Y swap would be the best
John: Lake Forest, IL
'57 Fairlane 500 - Looking better every day.
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Supreme Being
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NewPunkRKR (3/11/2010)
So basically what you're telling me is that it was not a great motor series and long term a Y swap would be the best
I would say that it's just as overlooked as the Y. After all, a version of the 400m has cleaned up at the engine masters. Something about 850hp on 91 octane and repeatedly winning the competition makes me hesitant to say that it's not a great motor. I'm sure it will respond to the same tricks that any engine will in order to improve mileage, tuning, increasing compression, balancing, better carb and intake, etc. But, if you can't control your foot, the same improvements can lead to worse mileage! Some Y-blocks, in there original vehicles and configuration are "gas hogs."
Lawrenceville, GA
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Supreme Being
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I would think another reason the Y would have good efficiency would be that it makes a lot of low end torque, so you don't rev up as much as a 351M.
Take it from a man who has spent a lot of time in his friend's Bronco: Do not make it your daily driver. The wiring is poor, the front ends always fail and take out four wheel drive, and they drink a bunch of gas. They're cool vehicles, but they just can't seem to go the distance every day.
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People should not be afraid of their government, a government should be afraid of the people.
--Alan Moore
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Supreme Being
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I would think that the 351m, with it's longer stroke and bigger bore will produce better torque. Does anyone have numbers? I can't find anything on the internet.
My Y is in the 8-10 area in the city and 13 on the highway, in 4th. My mileage really didn't change much with a stock motor compared to the modified motor in it now. It is probably an equivalent gas hog to the 351m Bronco. It has a lot to do with the total package, gearing, vehicle weight, drive line efficiency, aerodynamics on the highway and to a smaller degree on city roads, and the engine. On a big Bronco, many of these things are working against it.
Lawrenceville, GA
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