swapping 400 for 300 I6
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Senior User
Joined: Jun 2007
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swapping 400 for 300 I6
i am about to swap the blown up 400 in my 73 long bed for an I6 and ive done alot of searching on here and came up with nothing so i was wondering when it comes to the motor mounts and towers am i gonna have change anything or can i use the towers in it
Laughing Gas
Joined: Apr 2001
Posts: 868
Likes: 3
From: New Glasgow, Nova Scotia
The towers are not the same as the 300 I6, and the trans will need to be swapped if it's an auto and the bell housing will need to be changed if it's a std. trans. You may also run into driveshaft length problems. Good luck with the swap.
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Senior User
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well when i got the truck some one had put a 400 in it from a 77 i drove it a while till it gave up the ghost and then i bought a short bed with a 360 which is my daily driver but now i need somthing better on fule so im going with a I6 with a 4 speed
Senior User
Joined: May 2007
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I dont know why people like to bash the 300, sure its not the most powerful engine in stock form. But wow, a few mods and you have yourself a nice powerhouse with wicked low end and decent mileage. Motor mounts, bellhousing pattern, rad hoses (i recommend universals), ignition. I think thats all you really need to worry about to swap it in.
Posting Guru
Joined: Mar 2006
Posts: 1,213
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From: Parma, MI
No one bashed it. Its a GREAT engine. Just think it would be a downgrade going from the 400...
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Cargo Master
Joined: Mar 2008
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From: Goliad, Texas
when you're worrying about mileage I'd rather have 15-18 than 8-10.
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Lead Driver
Joined: Dec 2000
Posts: 6,302
Likes: 47
From: South central, Minnesota
I'm doing the same swap in my 78 F250 4x4.
Don't know if your truck is 2wd or 4wd. But to do the swap you'll have to change out the motor mount frame bracket/towers. You'll need ones from a 65-79 truck with either a 240/300 inline 6 or a 360/390 FE big block. They use the same brackets. If your truck is a 2wd you'll need the towers from a 2wd truck. If it's 4wd you'll need ones from a 4wd. And then just use the motor mounts for your age truck with a 300.
And like it was already mentioned you'll also need the correct bellhousing/transmission.
The 300 is a great engine.
Don't know if your truck is 2wd or 4wd. But to do the swap you'll have to change out the motor mount frame bracket/towers. You'll need ones from a 65-79 truck with either a 240/300 inline 6 or a 360/390 FE big block. They use the same brackets. If your truck is a 2wd you'll need the towers from a 2wd truck. If it's 4wd you'll need ones from a 4wd. And then just use the motor mounts for your age truck with a 300.
And like it was already mentioned you'll also need the correct bellhousing/transmission.
The 300 is a great engine.
Junior User
Joined: Oct 2004
Posts: 92
Likes: 1
From: Rock Island, Illinois
Has anyone done a swap of a 4.6L or the triton 5.4L into a 70 something F series? I had a 99 f250 with the 5.4L triton, and it had great power and I was getting close to 17mpg in town when I took it easy....???
Senior User
Joined: May 2007
Posts: 184
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Sorry.. I didnt mean to say that you bashed it, im just saying that it is an engine that doesnt get the respect it deserves. For the purpose of the swap it is a perfect choice.
Thread Starter
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Senior User
Joined: Jun 2007
Posts: 129
Likes: 0
I'm doing the same swap in my 78 F250 4x4.
Don't know if your truck is 2wd or 4wd. But to do the swap you'll have to change out the motor mount frame bracket/towers. You'll need ones from a 65-79 truck with either a 240/300 inline 6 or a 360/390 FE big block. They use the same brackets. If your truck is a 2wd you'll need the towers from a 2wd truck. If it's 4wd you'll need ones from a 4wd. And then just use the motor mounts for your age truck with a 300.
And like it was already mentioned you'll also need the correct bellhousing/transmission.
The 300 is a great engine.
Don't know if your truck is 2wd or 4wd. But to do the swap you'll have to change out the motor mount frame bracket/towers. You'll need ones from a 65-79 truck with either a 240/300 inline 6 or a 360/390 FE big block. They use the same brackets. If your truck is a 2wd you'll need the towers from a 2wd truck. If it's 4wd you'll need ones from a 4wd. And then just use the motor mounts for your age truck with a 300.
And like it was already mentioned you'll also need the correct bellhousing/transmission.
The 300 is a great engine.
alright man thanks for the info thats what i was really looking for but yeah 300 for gas milage my dad has the same setup that im putting in and he gets about 15 city and 20 highway and i really cant afford to drive the shortbed with 360 anymore it gets about 5 mpg
I'll have the Roast Duck
Joined: Jul 2002
Posts: 9,622
Likes: 110
From: Northshore, MN
I put a 300 6 into my 79 Bronco that had a 400. My mileage went from 10 to 15. Power wise, not much difference, though I only use it for snowplowing. You'll want 300 frame perches (or FE perches into the other holes) and a small bellhousing. Throttle cable for a 300, and the radiator can remain (400). here's a pic how I used the 300 rad. hose, and the 400 rad. hose and joined the two together using a "step-down" rad. heater. Also a flex hose on top.