400m,(how much power?
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Joined: Mar 2001
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400m,(how much power?
I am in the process of swapping a 400 in place of my worn out 351m, how much of a torqe and horsepower increase can i expect? , and what are your guesses on the total power output of a 1979, fully remanufactured, fully stock 400? horsepower and torque, and do you think if I treat this engine right it will last? how long? thanks, ya'll
Fleet Mechanic
Joined: Feb 2001
Posts: 1,290
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From: Toronto, Canada
400m,(how much power?
I think they are rated at 172hp. I am unsure at how many rpm.
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1978 F250 4x4 - 351M
Don't crush them, restore them!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
Fleet Mechanic
Joined: Feb 2001
Posts: 1,290
Likes: 15
From: Toronto, Canada
400m,(how much power?
I believe the 351M was rated at 150hp.
But with the 400, you will get much more torque.
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
But with the 400, you will get much more torque.
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
Senior User
Joined: Apr 2001
Posts: 128
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400m,(how much power?
351m=around 135 net horsepower
400=around 140 net horsepower (w/2bbl) but 300 pnd-ft of torque at 1,800 rpm.
You should get over 150,000 miles out of it if you don't mind a little oil spewage.
400=around 140 net horsepower (w/2bbl) but 300 pnd-ft of torque at 1,800 rpm.
You should get over 150,000 miles out of it if you don't mind a little oil spewage.
Senior User
Joined: Apr 2001
Posts: 128
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400m,(how much power?
I have 180,000 on my 351m and it's still running like a . . . it's still running!
Someone on one of these posts said that the 351m/400 is known as the comatose engine: can't kill it; can't wake it up.
That seems pretty apt.
Someone on one of these posts said that the 351m/400 is known as the comatose engine: can't kill it; can't wake it up.
That seems pretty apt.
Fleet Mechanic
Joined: Jul 2000
Posts: 1,493
Likes: 345
From: SE Iowa
400m,(how much power?
Comatose is about right! Had two cylinder with under 50lbs compression, three burned exhaust valves, and 5 worn down cam lobes. not to mention the crank was severly scored and had to be replaced. but it still purred like a kitten....okay maybe a sick kitten, but it purred. 
Stryder
Stryder
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Elder User
Joined: Sep 2001
Posts: 887
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From: Jax FL
400m,(how much power?
they were rated from 150-178 hp from the factory. if you have a clue and can read, one can get 380-700hp easy out of a 400c/m. the otrguq was 330 rated, and one can get 350-600+ ftlbs. its east to get this, hard to mess it up. as for waking it, yea i did that. real simple too.
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Junior User
Joined: Sep 2001
Posts: 66
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400m,(how much power?
Not a 351M, but my 351C was still going strong after approx 235,000 miles without a rebuild (about half of which were on LPG) and several seizures sue to overheating (caused by dodgy radiator). I sold the car and now it's in an F-series truck and still running fine last time I heard.
