So im new to this, and i bought a 56 f100 a few weeks ago, it doesn't run, the freeze plug has a hole in it and i wanted to know what you guys think. Should i keep the 390 or go to a pick n pull and get a 5.8?? Im 15 and i have some cash, but i dont need to pull 500+ hp. But i do want to have some fun with it and maybe take it to the track a few times. Any opinions??

 

You probably wont be any further ahead going to the junkyard. If its already setup for the 390, i would try and get it running before switching everything around for a motor that you don't know is in any better shape than the one you have.

 

Welcome to the forum. Probably a good idea to make sure you do have a 390 and evaluate the condition. A freeze plug is not a serious problem but does indicate lack of maintenance.
Has the 390 ever run while in this truck or is it someone's abandoned project? What are your visions for this truck at the track?

 

It ran until 1978 and was garaged for the rest of its life, yes its a 390 it has the sticker on the side of the valve cover.

 

Well this is a long time project for me, and its not too bad of condition, theres oil and dirt almost everywhere but ive pressure washed twice and gotten a lot off, it needs freeze plugs for sure, and i know thats not too hard but the motor mount is in the way

 

But for long term do you guys think i should keep the 390?? I could switch out to aluminum heads to try and lose some weight, but i know the 351 is a pretty solid block

 

I've had both engines over the years. The 390 is a big, heavy engine, but they do run pretty well. I would watch the aftermarket heads. The valve geometry on a 390 has very high angles. As the rocker arms rock, they put quite a bit of side load on the valves. The stock factory heads have relatively hard valve guides and will last well. Some of the bronze guides will be worn out in 10k miles.

The other thing is that a lot of 360s were sold as 390s....they are virtually identical on the outside, so I wouldn't rely on only the sticker.

I had a 390 in an F350 years ago....it was a truck that I used to tow a 5th wheel trailer around. It was a serious workhorse....but again...big and heavy.

I have a 351w in my 52 F1. I love it...technically, I bought a 5.8 out of an 89 F150, but built it up as an old school carbureted engine. I used a cam and timing gears that would have been stock in a 1969 351w in a Country Squire station wagon or a Mustang. It has plenty of torque and a very smooth idle.

All of that being said, I would follow the lead of the other guys....see what you have before making any decisions. Freeze plugs are easy....except the one behind the motor mount. I may be mistaken, but I think there is one hiding under the bell housing too. Start with a compression test. I can tell you from experience, that these projects can snowball on you...change the engine....now the mounts...then the exhaust. None are too hard alone, but when you put them all together, it will extend the total time for the project. You may do well to pull the engine, clean it up and replace the freeze plugs. Then...back in with it.

Dan

 

Thanks Dan! Yes i tried a compression test tonight and the starter is out, so i couldn't tell. But when i turn the crank over by hand it puts up quite a bit of resistance, but its not frozen. The freeze plugs are easy. I just dont want to waste my time and money if a 351 will serve me better in the end. I like the way you carbureted the 89 5.8liter, I was actually thinking about doing that myself. If anyone knows how much my 390 would go for? Just the engine?

 

Here's some things to keep you going:

Here's the block and trans before I assembled the engine....I did a lot of fit-up, mocking up etc to make sure everything would fit.



Here it is after the build-up....the small block 351 fits well between the frame members. The 390 would be more of a challenge to fit up....the main problem is to get the exhaust to clear the steering components. Since yours is already assembled, check the steering and make sure that there is some air space between the exhaust pipe and the steering gear box.

 

That looks great. How much do you think a fair price for a used 351 windsor engine would be? I think its my best bet. It can outperform a big block when its stroked, its lighter, and it gets better gas mileage

 

Welcome to the forum. I'm going to toss out a couple things to let you think. I love the fact that you're 15 and getting started in our hobby. That's how old I was when I got my first truck, a 50 F1, and built it to drive in high school. That was a long time ago. You'll have a lot of fun with this if you do it smart.

Changing out the 390 for something different will require everything else it's attached to to be changed. Nothing will interchange between your big block and any of the small block engines you've discussed, including mounts, transmission, exhaust and accessories. You'll be starting over completely from scratch, and that gets both time consuming and expensive.

You will not get any better gas mileage with the small bock engines, especially if you start to hot rod them with stroker kits, bigger cams, etc. Plus, you're 15. I know how 15 year olds drive. I still do. So that's not really a factor to consider.

In the end, you'll spend far more money trying to swap engines than if you stick with the 390. They're great engines and provide you with more grins per mile than you can ever imagine in your 56. Unless you can inspect it and find more damage than a blown freeze plug, put in a new one and try to get your existing engine running. If it's truly broken, a good, used FE engine isn't too hard to find if you look hard enough.

Good luck with your project. Keep us posted on your progress.

 

Thank you! yes illl keep everyone posted while i fix things, i think maybe ill keep the 390 for now then

 

I think you should keep the 390. Yes they are heavy, but they are also very heavy duty. I doubt a 351 would get better fuel mileage. I had two 352s (basically a shorter stroke 390) in 66 F-100s. One had a manual transmission with overdrive and a 3.50 rear axle, it got 16 m.p.g. The other truck had a manual transmission without overdrive and a 3.25 rear axle, it got 15 m.p.g. Just gear your truck to your engine, keep everything in good tune, and you will be happy with the 390.

 

Thank you all for all the information, I'll keep you guys posted on how things go and with the project all together! I appreciate all the knowledge and i feel the 390 is my best bet for the time being

 

Often it makes sense to do a little "extra", if the cost is reasonable. If one of your core plugs is rotten, all of them are suspect. It's real likely it was run without proper antifreeze, with anti-corrosion additives. A core plug costs a buck or two (get brass), do them all. Or you may blow $10 worth of antifreeze all over everything once it gets hot and up to pressure.