I understand that Ford used the same block for both the 360 and the 390. My engine needs some work (rings, valve job, oil pump replacement, seals).
I realize that costs vary across the country, but I'm thinking about having my 360 converted to a 390. Does anyone have a "guessestimate" about the cost of such a conversion? Does anyone think it's a bad idea, and if so, why?

As always, I will value and appreciate your input.

Paul

 

It really depands on what U want.. U can hit a JY and get one pretty cheap.. Here a Pick and pulls sell them for as little as $75. You will still need to go thru it.. but in most cases its a good start..

 

If you can get your hands on a 390 crank and a set of rods for a 390, then that is basically alls you need. Stick with the 360 pistons, as they will up your compression. There are some guys in here that will give you the details, but look at getting aholt of a crank and set of rods from 390, then you are set. As previously stated, you can get those from a junk yard in your area. Just be sure it's a 390, and not a 360 advertised as 390. If a recall correctly, 3.78" is stroked of 390 and 3.5" stroke is 360. Both are 4.05" bore. Do you know your head casting numbers? If not, what year is the motor? That will most likely tell us what heads you've got. (if it's stock?)

Mike

 

Converting the 360 to a 390 is usually a good idea. With stock pistons, the best you're ever going to do, compression wise, is about 8:1. And that's with thin head gaskets. Now, there is an FT piston that would give you somewhere around 8.5 or 8.6:1 compression in a 360. So if you're building a street motor there may be some options there.

There's more to converting a 360 to a 390 than simply putting in the 390 crank and rods. For one, it's going to need to be overbored. You may be able to ream out the ridge, hone it and get away with it, but I wouldn't take the chance. Besides, the 360 pistons are probably worn out anyway.

Second, your compression ratio will be significantly increased. You'll probably want a bigger cam so the thing doesn't ping itself to death.

Even then, you may not want 360 pistons in a 390. Depending on your head CC's, the pistons you use (replacement, stock, etc), and how you build it (head gasket), your compression ratio could be as high as 10:1! Now, if you're going for the high performance motor, this could be a good thing. But if you're going for a sane torque motor for getting good mileage, it might be a bit too high. Then, you'd be looking for aftermarket dished pistons, of which there are many options for a 390.

Then after you do this stuff, are you really going to want to run that anemic stock 2 barrel intake and carburetor? Do you really want to put those craptacular stock exhaust manifolds back on it, when headers help so much?

So yeah, there's more to it than just crank and rods. It's usually a good idea to convert them, but to do it right it costs more than you might think.

 

I'm also thinking of doing the same thing for a 360 I have. Just don't know if is worth it or not. The engine only has about 23,000 miles on it, am planning to replace the intake, carb and exhaust manifold. Will probably replace the cam while at it. Is in a 68 F350 and will be used primarily for heavy hauling so would like the extra torque of the 390. Think can get the crank and rods from salvage yard without any difficulty but then would have to go ahead an pull the whole motor.

 

Great post! I have been think about doing this for a while. No one mentioned the heads. Can I use the 360 heads on the 390?

Thanks

 

yes, you can use 360 heads on a 390 and visca versa.

I priced out changing my 360 to a 390 using edelbrock performer rpm heads, cam, and intake. estimate came to about $2500....and i still have to find a 390 for the rods and crank. The only rebuild kit i could find to get the bearings, pistons and gaskets in one package was from summit and they only had .020-over bearings available. Site sponsor Jegs didn't have anything.

 

I started looking at parts to convert the 360. What I found that the rods for the 390 were the same as the 360. Is that right? If it is then the only difference is the crank. What are your thoughts

 

That is most definately wrong.

360 rods = 6.54" center to center length
390 rods = 6.488" center to center length

 

if you can find a loose 390 buy it and rebuild it as a 390

save your 360 for later or sell it

this would keep any guess work out of the equation

just depends on the price of a complete engine vs. the crank and rods...

however a complete engine gives you a lot of extra small parts and accessories and having to FE's gives you a reference as you assemble your final engine.

 

I agree with rusty!!! i did this same build ..... just to take it to the shop and get a short block it was about 1100$(bored +.30. evrything plained the whole nine) but I got hooker headers(headers are a must) edlebrock carb(600cfm) comp cam and timing set ,4 barrel manifold of a 65 thundrbird at the JY. the list goes on and on so it gets more expensive than you think ....and fast!!!!! im prob around $3500 at this point....lol....well worth it though in my opinioon..... just a warning carefull of the cans you open...lol....good luck

 

Regardless you think change over from the 360 and get that 390 built!!! What a frickin difference!! I ran my 360 that had 128,000 on it when i got it for about 3 years and it got 8mpg at best and was a dang dog! Then i put 390 crank/rods, kept my pistons, 343941 crane cam, holley 600, stock 4v intake. Well worth your time/money. Great investment especially if you're gonna get into hauling/moving things. You'll get it done faster,easier, and much more efficiently with the 390. I've gotten 16 mpg already w/ only 1500 miles on my new 390! I still have got to get my heddman elites and tune in my secondaries and then I'll really know what a 390 is made of. Anyways by all means build a 390 if financially possible!! Just pray that tires start growing on trees!

 

Yes a 390 crank and rods will fit into your 360 block if you use the 360 pistons you will end up withy a fairly high compression ratio requiring use of higher octane fuel. I tink just upgrading with 390 crank,rods and pistons is a good idea if you want more torque on a budjet.Or just finding a 390 and rebuilding it, thats what i'm doing now. I'm lucky enough to have gotten a fairly low mile motor that's got almost no wear in the bores good rotating mass with acceptible clearences.I'll have the block tanked put in new cam bearings and frost plugs,hone it, rings, bearings,oil pump,lifters,valve job and get away with less than a grand into it.There is a post on here right now with an e-bay listing for a complete rebuild kit with pistons for a buy it now price of $420.00