Can you put a '78 engine into an '81?

[OmriWithHis81]

Hello! I'm a new member here but a long time researcher. I'm starting to get serious on a project taking place with my first truck, a 1981 F250 with a 300, granny low BWT19, and is 2wd.

I'm going to be building an "underdog" engine. A 400. And when I say build, I mean buy one, strip it down, go through it, clean it up, throw some parts at it, and call it a day. Not machine shop or bore it or anything, something achievable for a 17 year old with minimal help. But this is where my questions start in reference to dropping it into my truck.

I have a lead on a 400 that's out of a '78 F250. I'm not concerned with mileage and I know it was running less than a year ago.

Question #1, will a 400 out of a truck before 1980 (79-below) be able to set into a 1980-86 frame with 80-86 351m/400 motor mounts, or will there be positioning issues?

Question #2, for electronics of the 400, what will I need to find? Is the wiring harness going to be a hassle between an I6 to V8? Will I need to find a new ECM/V8 specific one for 1980-86?

[85pig]

You're going to need the engine perches that bolt/rivet to the frame to go with the 400 motor mounts. The 300 bolted directly to the crossmember on the Bullnose trucks, the V8s got engine family-specific perches that were riveted to the backside of the crossmember. They can be changed out by grinding/cutting the rivet heads off, and then bolting to the crossmember and frame.

If you're running the Duraspark II ignition setup, you'll likely need the 351M/400 harness that runs from the cab to the ignition module, distributor, and coil. With the correct junkyard harness, that should be a plug & play situation. Only minor snag will be if your truck has a tach or not. Not 100% certain, but I don't see why any of the V8 harnesses wouldn't work, as long as the length is adequate. If you're running a carb on that 400 (and you most likely will be), you won't need to worry about any of that ECM stuff.

[OmriWithHis81]

You're going to need the engine perches that bolt/rivet to the frame to go with the 400 motor mounts. The 300 bolted directly to the crossmember on the Bullnose trucks, the V8s got engine family-specific perches that were riveted to the backside of the crossmember. They can be changed out by grinding/cutting the rivet heads off, and then bolting to the crossmember and frame.

If you're running the Duraspark II ignition setup, you'll likely need the 351M/400 harness that runs from the cab to the ignition module, distributor, and coil. With the correct junkyard harness, that should be a plug & play situation. Only minor snag will be if your truck has a tach or not. Not 100% certain, but I don't see why any of the V8 harnesses wouldn't work, as long as the length is adequate. If you're running a carb on that 400 (and you most likely will be), you won't need to worry about any of that ECM stuff.

I need a wee bit of clarification, I'm trying to learn as much as I can before tearing everything apart.

#1, So the 300 goes from crossmember to mount, where the 400 goes crossmember, perches, mounts?

#2, Will I have to grind off/drill out the old motor mounts of the 300 from the crossmember?

#3, Are the mounting holes already in the crossmember for the perches?

#4, If the engine perches are separate from the mounts, is there a place I can buy them, or will I have to find a 400 specific crossmember/have to rob the perches from a junkyard? (Where I live the closest junkyards that are pick and pull are about an hour and a half away)

Thank you in advance, I appreciate all the knowledge you can offer to me.

[mat in tn]

I need a wee bit of clarification, I'm trying to learn as much as I can before tearing everything apart.

#1, So the 300 goes from crossmember to mount, where the 400 goes crossmember, perches, mounts?

#2, Will I have to grind off/drill out the old motor mounts of the 300 from the crossmember?

#3, Are the mounting holes already in the crossmember for the perches?

#4, If the engine perches are separate from the mounts, is there a place I can buy them, or will I have to find a 400 specific crossmember/have to rob the perches from a junkyard? (Where I live the closest junkyards that are pick and pull are about an hour and a half away)

Thank you in advance, I appreciate all the knowledge you can offer to me.

I generally only work with bullnose so I'm coming from that perspective. the k member/frame is different and sits a bit forward and the oil pan may need to suit. earlier than the bullnose, the 302 had a front sump oil pan and the steering system sits behind the sump. this is only one example yet it's worth looking into. I have an f250 with the 351m and it is the same with the rear sump oil pan and it sits very close to the frame. about 5/8" at one point. I cannot see a front sump fitting at all.

[Gary Lewis]

I need a wee bit of clarification, I'm trying to learn as much as I can before tearing everything apart.

#1, So the 300 goes from crossmember to mount, where the 400 goes crossmember, perches, mounts?

#2, Will I have to grind off/drill out the old motor mounts of the 300 from the crossmember?

#3, Are the mounting holes already in the crossmember for the perches?

#4, If the engine perches are separate from the mounts, is there a place I can buy them, or will I have to find a 400 specific crossmember/have to rob the perches from a junkyard? (Where I live the closest junkyards that are pick and pull are about an hour and a half away)

Thank you in advance, I appreciate all the knowledge you can offer to me.

We have a page that includes pictures here: https://www.garysgaragemahal.com/engine-perches.html. That might help you answer some of the questions.

[85pig]

I need a wee bit of clarification, I'm trying to learn as much as I can before tearing everything apart.

#1, So the 300 goes from crossmember to mount, where the 400 goes crossmember, perches, mounts?

#2, Will I have to grind off/drill out the old motor mounts of the 300 from the crossmember?

#3, Are the mounting holes already in the crossmember for the perches?

#4, If the engine perches are separate from the mounts, is there a place I can buy them, or will I have to find a 400 specific crossmember/have to rob the perches from a junkyard? (Where I live the closest junkyards that are pick and pull are about an hour and a half away)

Thank you in advance, I appreciate all the knowledge you can offer to me.

I may have been steering you wrong.

***After further review, I'll need to look into that more; the six may in fact have perches that mount on the crossmember. There is a hole in the crossmember that is covered by the 300's perches, that looks to be an access hole for the V8's oil filter? If so, then yes - you'll need to remove the 300 perches too. And that sucks.

[ArdWrknTrk]

The 400 is a DS-II engine, you can use the same module but because the 300's oil, water senders and distributor/coil are in far different locations you will have to shorten & extend the engine harness accordingly.

Matt brings up the point of front vs rear sump.

All the front sump engines I've seen have the dipstick in the timing case.

You might look into E-van engines because of this.

The 351M/400 uses a 385 series bellhousing pattern.

You will need a transmission from a M/400 or a 460 to bolt to that engine.

[Nothing Special]

.... The 351M/400 uses a 385 series bellhousing pattern.

You will need a transmission from a M/400 or a 460 to bolt to that engine.

If you're sticking with a manual trans you can probably use the same trans, but you will need a bellhousing from a 351M/400 or 460. I've never looked for one, but I've heard they can be difficult to find.

And I'm thinking the '81 has a mechanical clutch linkage rather than hydraulic. But whatever it has, you'll need a bellhousing with the same kind of clutch linkage as what you currently have.

[ArdWrknTrk]

.... The 351M/400 uses a 385 series bellhousing pattern.

You will need a transmission from a M/400 or a 460 to bolt to that engine.

If you're sticking with a manual trans you can probably use the same trans, but you will need a bellhousing from a 351M/400 or 460. I've never looked for one, but I've heard they can be difficult to find.

And I'm thinking the '81 has a mechanical clutch linkage rather than hydraulic. But whatever it has, you'll need a bellhousing with the same kind of clutch linkage as what you currently have.

Yep, manual linkage until 83 when the 460 replaced the 400.

But you're definitely going to need -at least- the bell housing and release fork from a 400.

I know the 70's frames are far different than '80-96 and use front sump pans, so the perches from a '70's truck are not going to fit an 81 engine crossmember.

If you have the engine out and are looking for a strong engine get yourself a straight up timing set and a 4V intake and carb.

Gary can offer advice on the 335 engines.

 

[OmriWithHis81]

We have a page that includes pictures here: https://www.garysgaragemahal.com/engine-perches.html. That might help you answer some of the questions.

With all the given information, including sump position, perch placement, and transmission bolt up, I've thought of some possible solutions.

If the frames before 1980 had been different and offered a different oil sump position that might not work with a later crossmember, would it be easier to find a 400 out of an 80-83? I'm not dead set on this 78 engine, just had been one that came up and had been close.

For pictures of the perches, all it looks I'd have to do is remove the 300 perches, and purchase ones for the M-block to bolt on.

Transmission bolt up, I can confirm first hand is manual linkage, and I haven't yet decided what I'm going to do regards of finding a bell housing or replacing my transmission as a whole. I'm swapping out my Dana-60 for a Dana out of an 84 that has 3.54s and an LSD.

With all of this I might go to the guy I'm getting most of my help with and tell him these things. A change of plans with this project might me in order, and that's why I wanted to come to people with knowledge.