390 or 400 with 4 speed Hum which one should i use

[jstephenson]

I have several trucks a 76 w/390 and 4speed, 79 w/400 c-6, 78 w/4 speed. Have had a 390 always thought it was a good motor. Don't know much about the 400 but have been told that it is a gas hog and a lack of power. Basiclly customizing a 79 super cab 3/4 ton 4x4 that the cab and bed is trashed going to use a reg cab w/ super cab frame w/ front long flat bed and a 5th wheel set up for pulling my 29' fifth wheel trailer. With that in mind does anyone have any comments or ideas. Thanks again for the imput
Jeff

[havi]

http://www.ford-trucks.com/forums/66...-400-swap.html For all that weight, I'd flip the bill for a 460. Or even a diesel. My 2 cents.

[jstephenson]

hey I kinda had the same thought thats what i have in my 78 f-250 I just have to find a good one

[jstephenson]

so the 400 perches will fit the 460 but not the 390 is that what i'm reading please verify, because i'm a believer in the 460

[havi]

In a way, yes. The cheapest $$ motor mount adapters are for 460's going into the 351m/400 trucks. It costs more to put one in an FE equipped truck. Why, I dunno, it just is. But, I've heard from several sources that flipping the 390 motor mounts and drilling the 3rd hole for the 460, allows the 460 to fit where the 400 was. But no, you can't just drop the 460 into the 400 equipped truck. adapters, like from LandL, or Jeff's bronco graveyard, or AdvanceAdapters, etc...Unless you use the mounts and perches from the truck that already has the 460, unless the f250 is 2wd. All in all, if the truck originally had the 400, then your options are really good.

[jstephenson]

so then I think what you said is that you use the mounts from the 390 but on opposite sides and making a new hole will work what if they are from a 4x2. sorry still trying to learn all the little secrets. If i get another 460 i need towers and mounts if possible from a donor truck 4x4 that came equipt with the 460, and i need another
flywheel. I have a new one for my conversion on my 78 originally with a c-6

[jstephenson]

also will the new 460's bolt up to the older 4 speeds so i can go with efi

[1EVILCREWCAB]

whatever you do stay AWAY from the 400, by the time I made power with one it still wouldn't keep up to the connecting rods falling out of it, Ive got the same truck you have except f-350 and a 460 based big block is a fairly straightforward swap, I used mounts off the front of the heads so i had room for in frame headers with a turbo, i'm running a 528 cube big block on lpg with 22-25 psi boost, nothing beets cubes for power!

[jstephenson]

got any pics of that set up. we live in a mountainous area and i pull a 29' 5th wheel and i don't want to be the last one to the top of the hill you know what i mean and what fuel mileage if any do you get

[havi]

I'll gladly take yer 400's.

[1EVILCREWCAB]

I'm not able to get any pics on here, I can tell you one thing though don't be cheap on the engine build! I've got roughly 10 large in my shortblock to keep up with this power level, when i'm not on it (rarely) i can go 75 miles on 10 bucks, better than the wifes minivan! when i've got my foot stuffed through the firewall and into the grille (most of the time!) I have drained a 300 litre (75 gallon) tank in under 1/2 hour, check out my website www.jm-custom-mechanical.com , i've got a few pics you might enjoy on there of my junk, drop me an email if you like and I will send you some pics of my setup

Originally Posted by jstephenson

got any pics of that set up. we live in a mountainous area and i pull a 29' 5th wheel and i don't want to be the last one to the top of the hill you know what i mean and what fuel mileage if any do you get

[Matts72]

Wow... I'm calling total BS on that... 25 MPG with a 528/460... 25psi boost would put you around 16:1 compression ratio and you aren't going to ignite that with anything less than 125 octane, and Propane is even worse...

The 390 and 400 are both good motors... I've built them both for power and currently use a 400 in a comp mud truck.

[ncl]

I run a 400 in my truck it is a 77 f150 4x4 reg cab long bed, The motor just has a mild cam, dual plane intake and 600 cfm 4bbl carb, stock exhaust manifolds. I have 4.10 gears and 36" tires on the highway I get 10 mpg. A 460 may get better mileage cause it wouldnt work as hard but probably not more than 2-3 difference. If I had headers the mileage would be better. If you really wanna find out what a 400 can do talk to TMI or Danlee in the 400 forum. The 400 is a stump puller of an engine and cheap to upgrade.

[1EVILCREWCAB]

25 mpg? not sure how you figured that out, 38 cents/litre x 4.4 litres/gallon $1.67 gallon, 6 gallons = 10$ 75 miles divided by 6 gallons = 12.5 mpg, actually, under full boost ,25 psi, compression works out to 17.6:1, with -28 air intake temps, 150F cylinder head temps, custom combustion chamber design , works fine, max power is 1073 hp at the wheels 900+ lb ft torque, note that under full power I have burned 75+ gallons in under 1/2 hour, that works out to gpm (gallons per mile), propane is 120+ octane, injected as a liquid at -44f has a wonderful cooling effect, how do you think guys are making 1000+hp on nitrous? add a little water/methanol vapor here and there, combustion temps are 1375f, NO ELECTRONICS! I LOVE PROPANE POWER!!!!!

Originally Posted by Matts72

Wow... I'm calling total BS on that... 25 MPG with a 528/460... 25psi boost would put you around 16:1 compression ratio and you aren't going to ignite that with anything less than 125 octane, and Propane is even worse...

The 390 and 400 are both good motors... I've built them both for power and currently use a 400 in a comp mud truck.