I have a 71 F250 4x4 that I want to convert the 360 into a 390. I know I need 390 crank and connecting rods and I plan to use my 360 pistons as I have read they actually will have a higher compression since they were used in 390 car applications. Top end has been redone with an edelbrock 4 barrel and their 72cc heads as well as a comp cam. Truck runs good it just doesnt have to power I want to tow and pull hills. So my question is can I do this swap from underneath the truck so the motor doesnt have to come out? Any insight is appreciated.

 

No. The pistons come out the top, so you can't do it all from below.

You could do it, but you risk a poor result due to the difficulty in keeping things clean and checking bearing clearances, getting pistons lined up and a few other things that will pop up.

 

It seems like it would be WAY more work than pulling the motor to even try. Why the aversion to pulling the motor? I just pulled mine by myself in about 6 hours or so. But if you must do it the hard way, I think you are going to be into this a lot more than 6 hours...

Working this out hypothetically, you would have to drop the transmission in order to unbolt the flywheel or flexplate from the rear of the crank. There is no other way to reach the 6 crank bolts. This would leave the motor balanced (probably not well either) on the two motor mounts. SO you would have to find some way to stabilize the block. Usually, this would be done with a jack or something under the oil pan, but that wouldn't work in this case. To clear the front of the crank, the harmonic balancer and timing cover have to come off. The balancer is easy enough, but to get the timing cover off, the water pump and all front engine brackets (alternator and power steering at a minimum) would have to come off. Once all of that is off, you have to drop the timing chain. Then comes the fun part. I'm assuming the pistons will even come out the bottom of the bores. IF you can, there is likely no way to get them back in unless you can find a ring compressor that by luck could work from the bottom side, but I doubt it. And if you can solve the piston re-installation from the bottom, you still have to unbolt the rods and shove them all the way back up the cylinders to clear the crank throws to in order to rotate the crank to unbolt the others (you can't do them all from one position). And I am not 100% sure that the rod bolts will clear the throws even when they are touching the heads. So realistically, the heads would have to come off and thus the distributor and intake manifold too. Even though you have an aluminum intake, that thing is still a beast to pull when the motor is in the truck. I suggest a strong helper- you'll need them in a minute anyways. So now that you have the engine 3/4 of the way to a full tear down and all the rods are out, you could finally try to drop the crank. The rear main bearing cap with the rear seals wedged in the sides is a pain to wiggle out even with the engine on a stand. It would probably be best to fight it first and then the rest of the main caps except the middle. Get your strong helper under the truck with you and then unbolt the middle cap... and figure out that crank is HEAVY when you have to catch it. At this point you will discover whether there is adequate clearance between the block and cross-member to actually get the crank out of the truck... or not. IF there is, then you have to wrestle the heavy crank out from under the truck while on a creeper. Then you have wrestle the new one back under the truck and bench press it into place...up and over the cross-member... and pray your arms hold out while a helper starts the main bolts. Repeat the bench press and pray routine at least a couple times while checking bearing clearances and thrust tolerances. Then install each connecting rod at least a couple times while checking clearances on those. Then put the heads back on, wrestle the intake manifold back into place. Oh and plan on doing this part again later to try to fix the leak on the rear china wall that almost always happens when intakes are installed in-truck. From here it is mostly downhill to just reinstall all of the rest of the stuff you took off.

Just pull the motor, you'll thank yourself later.

 

Wow. Jeremy! That was a COMPLETE answer. I feel like you just gave a lesson in "Do things right the first time so you don't have to do them over, and over, and over again" Thanks!!

 

I was just hoping there was a quicker way than pulling the motor. I had thought someone told me you can do it from below. Is it actually worth the hassle to make it a 390? I feel like all the work I did on the top end should have gotten me more than it did. Towing 1500lbs the truck struggles more than it should. My dads 77 with a 400 seems to handle a trailer much better and its stock.

​​As far as sourcing a 390 crank and rods is it better to find used or buy new? Im assuming anything used would need to be gone over by a machine shop?

 

Yeah, pulling the motor is pretty much the fastest and easiest way. It is possible to change the rod bearings from below and the mains are POSSIBLE too, but usually they are worked into place with the crank still in. And even that, most that I have seen do it that way don't really recommend it. Pulling the crank is a whole other animal. It's not a totally easy job to pull the motor, but like I said I did mine without help and it was well under a day's work. It is worth the hassle of conversion, or so everyone that has done it says. I just dropped my parts off at the machine shop today for a rebuild and I am doing the conversion as part of it. I will let you know first-hand in a month or so, lol.

The 360 was designed with pretty low compression so it just maxes out quickly as you have discovered. I don't think the performance increase is all from the extra 30 cubes, but the longer stroke and higher compression. You might be able to achieve similar results with just raising the compression of the 360 with new, probably custom pistons, but I can't recall seeing anyone try. Most just go for the 390 or a stroker crank while the engine is already on the stand. As far as sourcing the parts, it depends on your budget. The used 390 crank & rods is much cheaper, but yes definitely have it checked out. I haven't seen any available new, but I didn't look that hard as I already had a used one. My shop quoted me only $145 to regrind it if needed, so it's not terribly expensive. If you have the money, stroker kits are available new and can give you even more power, but they start around $1600 from the ones I looked at.

 

Yeah I would be interested to hear how it turns out for you. I think I'll probably enjoy the truck for a bit longer and then start the swap come winter if I haven't changed my mind by then.

If I were to find a 428 crank would 390 rods and my 360 pistons work? I read a 428 crank will bolt right up it just needs to be internally balanced but couldn't find any info as to what rods and pistons would work with this setup. And I would assume the 360 flywheel would work with this crank or a 390 flywheel for the bigger clutch. I just think it would be super cool to say its a 410 just because its different.

 

You can post your questions at the following. They're a bunch of FE nuts and are very helpful.

FE Technical Forum

 

Add up the crank throw, rod and piston compression height, and compare your total to the FE deck height of 10.17".

1.99" + 6.49" + 1.77" = 10.25"

410 pistons used a compression height of 1.67", which gets you to 10.15". + or - depending on the actual specs on the parts you get. The 410 was billed as 10.5 CR.

The same spec piston was used in 390 pickup engines. That resulted in the down the hole low compression Ford wanted for pickup engines.

Another member here said that for the money he had in doing a 410, he would have gone for the 445 if he had to do it again. The hard parts differ a little in price, but the labor, gaskets and machine work if needed are the same.

These are car specs for the FE.

FE Series Engine Specification Chart

 

Once he's done stripping the engine block of everything to do the job (inframe) only thing left is the motor mount bolts holding the block in the bay. So, yea the whole engine needs to come out, no sense in trying to assemble the shortblock inside the engine bay.

 

Before you go nuts, and YES I know the 360 is a gutless pig, I had one, but it could at least pull 1500lbs.

If it's struggling, you might want to look at a few things.

Timing, both initial, and total, and how fast the total comes in.

Are you sure the carb is not running either rich or lean under load? Or, the fuel pump can't keep up for some reason?

Was the gearing ever changed? And what is the current gearing? And is it still the 435NP transmission?

 

The truck will pull 1500lbs ok but not like my dads 77 with a 400. Initial timing is 10, not sure of total. The carb is good I adjusted it for highest vacuum but thats not to say the jets couldn't be changed a bit. Gears are still stock 4.10s with the stock np435. Truck is lifted 4in on 35s which arent super heavy so not anything crazy.

 

Tan71Bump, I too have a 71' F250 with a 360. I have no real complaints but I am also going to build a 390. If you have the $$, could you find a 390 short block and start the build now? When you're ready just swap your heads, intake, and carb onto the 390 short block?