I bought my '79 F150 about 4 weeks ago and have slowly be going through it to get it roadworthy. Hopefully it will be good to go once I get the carburetor rebuilt and the brakes gone through. It looks like I'll have to completely rebuild the rears and maybe turn the fronts.I might as well, I have to replace a broken lug on one side and might as well do it while the hub is torn apart, since I'm doing the one I should do the other.

Anyway, the truck has a 400 in it right now but the original 351M with approx 150k logged was included in the deal.

Ideally I would like to get the truck running for now then rebuild the 351 and swap it back over. However, cash is pretty tight right now and I don't know if I can afford to actually do it.

Here's my options as I see it.

#1- Save my pennies and eventually get it done, then sell the 400 for whatever I can get out of it. Pro: is in the original configuration with the actual original engine. Con: time & $- some will be recooped by selling the 400.

#2- Sell the 351M for whatever I can get out of it and apply the cash towards getting & keeping it running. Pro: cash now. Con: non original configuration and a drive train I am not sure about the condition and if it will need rebuild anyway.

#3- Find an engine shop that will rebuild the 351 and take the 400 for partial trade. Pro: same as #1 but faster. Con: don't know whether the build will be good, or if the cash will be available in time for the transaction. Shops need to pay their bills too.

I'm not sure what other options might be out there or whether having an original engine is something to be excited about. Does the 400 have any advantage over the 351M or vice versa?

 

If the 400 is ok, I'd stay with it. After all, the 400 and the 351m are really the same engine.

Maybe the 351m really has "only" 150k on it, and maybe it really does run. Maybe not.

You didn't mention how many miles are on the 400, but maybe rebuilding the 351m in prep for swapping it back in (when need be) is a reasonable thing to do.

 

IMO.....I'd keep the 400. They are externally the same. If the 400 is running good, dont mess with it until you have the funds. My truck originally had the 351M and it was a good engine. You've probably read countless threads on how horrible the 351M is or even the 400 for that matter, but I totally disagree. They are both good engines and can be built to be stout motors with some good aftermarket parts. It wont ever be a 460, or a 390, but also keep in mind what your long range goals are for the truck. Might also go over to the 335 Series engine section here on this website and just start reading. You will see what I mean.
When I did my engine swap, I had to rebuild it anyway and I wanted to go with a 429, but funds (or lack of) was the issue, so I decided if I want more cubes it made the most sense to build a 400 that will drop in and use my Edelbrock intake and also bolt up to my already existing headers. Im happy with the choice I made and it doesn't get any worse MPG than the 351M. But thats just me....

 

I don't know how many miles the 400 has. I talked to the owner that did the swap. He owned it from '80 with 12k until 2 mos ago. He parked it in '98, the 400 was put in about a year before that but he didn't say whether it was a rebuild or just a take out. He was going to rebuild the 351, which was running when it came out, himself but life happened and he never got to it.

 

Helpful input, thank you. I would eventually like to get it all fixed up to tip top shape but in the meantime it needs to be a driver and occasional short distance hauler.

I should mention this was a complete swap and absolutely nothing was transferred from the one block to the other, not even the carb. The exhaust manifold and a bunch of brackets and other misc parts are still in the bed of the truck.

 

I am a purist, I say try to get it back to the way it came stock.

 

I tend to think this way too. But I don't know if I'll manage.

 

I agree... in any case, the first thing is to get it running and put a few hundred miles on the 400 in the truck. Then you will have a better idea what shape its in. Even if you do decide to re-build the 351, you will know how urgent it is.

 

That is a point I had considered also. Someone at the parts counter mentioned the number on the carb tag suggested it was out of a '77 or at least some time prior to '79. It could have 350k on it for all I know.

 

I can agree with this if you are going for the 100-point show truck but if you are looking at a daily driver just run with what you have. From the outside nobody will know if you have a 351m or a 400. Who cares? Make the truck safe and dependable and enjoyable to drive.
Save your money and don't worry about the 'proper' engine.

 

Do what fits your budget and you like, that's really the major Factor on any project.

 

100% original is great for a rare $50K Shelby but on an average $3K truck a little custom personality is a good thing . Go ahead and add some headers , aluminum intake , and mag wheels . Unless you Dad bought it new it is just one of a million .

 

"Pure" 351m is "Pure pooch". Get some decent pistons and keep the 400.

 

Pure pooch? The only thing the 400 had going for it stock for stock was 49 more ci. It burned more fuel but not much else. Either engine needs higher CR, head work, a 4 barrel, etc. before its anything great, BUT neither engine made enough power to hurt itself when stock and for that reason they were reliable, had good torque and did what was asked of them much like the 300 Six.

With a bit of work either one can make the truck fun to drive.

I'd say that if you really want the stock engine in it, set it aside until the time comes and start building it, the other thing you could do is have a 400 crank to stuff in it during the build, on the outside the numbers will still state 351M and no one will ever know.

 

Do you want to be a purest and keep it numbers matching? Then fix up the 351M. Its really up to you and what you like to do with your truck.

My build I was going to put a 460 in but after some thought I decided to replace my 400 with another 400 create engine. Some of the things that influenced my choice was cost, time, my skills and weather or not I wanted to keep it numbers matching. My truck is not a daily driver but I do use it for work every now and then just because its fun to drive and l like to show it as well sometimes.

My suggestion would fix up the 400 so it runs reliably and build up the 351M as time and funds permit but keep a schedule with your build so it doesn't just sit around and gather dust. Projects get done best if you are not rushed, plan your work and you pace yourself.