Hello all!
I bought a 1980 Ford F150 for sentimental reasons. My dad had this type truck and I always loved it so when I saw one for sale on facebook I jumped on it well aware it would likely need some TLC. Overall it is in good condition but it needs a new engine. It is an automatic 2wd.
I would also like to say that I'm extremely new to anything auto mechanic related but my boyfriend is pretty handy in this area but unfamiliar with classic trucks.

It's a 351M 5.8L and I've been doing my research on what I could replace it with. It's proven to be pretty difficult to find a replacement 351m but from what I've read I might want to upgrade to something better anyways? I've been reading about swaps to a 460 engine. From what I've gathered it seems like it would just need some modifications but otherwise not be too difficult.

just wanting to make sure this is a possibility and what all would be involved in modifications?

So far I believe I would need to adapt the motor mount, modify the throttle cable as well as exhaust.. maybe different oil pan and manifolds or no?

Also I have read that the 351M/400 is in the 335 series whereas the 460 is in the 385 series. I read people swapping 351M for 460 but would it be easier to just go to a 400 where they're in the same series or does this not matter so much?

Sorry if this is long-winded I'm hoping somebody can point me in the right direction though I appreciate your help in advance!

 

Just about anything can be done if you have the budget for it. I say that because $$$ is generally the most limiting factor. Normally a rebuild of the original motor is the most economical option (1-5k) depending on current engine condition and how much you can do or get done for free.
A replacement with a simular motor (small block Ford) would be simular (2-7k) in costs to the rebuild depending mostly on the condition of the motor you choose to replace it with.
Replacement with another type of motor (big block Ford like the 460) will cost the most. (your budget is the only limit) motor mounts and transmissions will be different. Lots of custumizations may be needed and may be expensive.
So basically its up to you and what you are prepared to do yourself and the $$ you are willing to commit to the project. Note my $$estimations are based on my own ability to do much of the work. If you have to pay for the labor expect those estimates to multiply by 2-3x. But your vehicle would likely be most valuable as a rebuild with the original 351m if its still usable.

 

The 400 is the same engine basically as the 351m. So the 400 would be a direct swap. Just the guts of the engine are different.

The 460 is a different engine family, but it just so happens it has the same bellhousing pattern as the 351m/400. So you could re-use your same transmission, maybe. You are correct on your list of modifications for the 460, except sometimes the 351m used a smaller diameter flywheel or flexplate, while the 460 always used a larger flywheel or flexplate. This larger flywheel may rub on a 351m transmission bellhousing you just have to try it. You didn't say what transmission you have.

 

Check the "related topics" below, you may find some help there.

Just saying, if you put a heavier engine in, you may need to do suspension upgrades... ?

 

Welcome to the forum! Congratulations on your jump into the wonderful world of old Ford trucks. Having something that gives you a connection to your dad is a great thing, and when you get this all sorted out I think you'll have a ball with it, driving it and reliving all those old memories. You've also done real well in your research and most of what you've learned is somewhat accurate.

I'm going to suggest for your first project we keep it simple. You didn't say what's wrong with your current engine that it needs replacing, but assuming it's just tired, a rebuild is in order and a stock rebuild will be the cheapest and easiest option. There's nothing wrong with the 351M engine. They may be a little down on power compared to other options, but if you're just looking for a fun truck to drive and do all the things we discussed at the beginning, it will be perfectly fine. Staying with the same engine family will help with the keep it simple plan. Changing to a 460 is done, but comes at a cost and a lot of work and buying a lot of replacement parts that's totally unnecessary if you stay with the 351M/400 335 family. Since this is your first rodeo, I'm going to suggest we save that work for a later project. Biting off a big chunk like an engine swap right off is something you could choke on, be above your immediate skill set and sour you on the whole deal. I'd hate to see you get lost in the minutiae and lose interest.

If you have a burning desire to upgrade, swapping some of the internal guts; crank, rods and pistons to 400 parts, will gain you the additional displacement and power. The cost isn't going to be any different than refurbishing your 351 parts, so it could be a worthwhile investment. It all depends on what you want. Those parts are a direct retrofit as both displacement engines use the same block and everything else on the engine. If it were me, that's where I would go and the machine shop you choose to do your rebuild can help you with that. You might talk to a few machine shops in your area and see what they say. Get some opinions and some prices. Follow up back here and let us know what they say. We're here to help you stay on track and make sure you're getting the straight scoop. You might also post a pic of you with the truck. We like pictures. Good luck with your project. Keep us posted on your progress.

 

I have an Australian R/H drive 1986 F 350 4WD that originally was fitted with a 302 Windsor 302 fuel injected engine, I replaced it with a more commonly available here in Australia 351 Cleveland 4bbl engine, it was an easy conversion utilising the same bellhousing and New Process 435 gearbox.
It provided more power than the Windsor and is still going strong in 2025.

 

Have you considered just buying a remanufactured 351M long block? You can probably get one for about $2500 and then you don't have to worry about a complex swap. I have done a swap, its not for the faint of heart.