alright well i pulled the stock 351 and put in my 400m, now the frame is untouched so its unboxed, and im worried that 350+hp (unknown torque) will twist my frame or have really bad flex to the point of popping open doors or breaking windows (my buddies dodge dart with blown 426 hemi does it)... anyone run into this problem before?

 

if all your oem crossmembers are in place this problem seems highly unlikely.
then again miracles happen.....

 

I agree, My SBC 400 doesn't twist the frame or open doors. The cab is well insulated from the chassis unless you solidly mounted it. The Dart is unibody and he probably has the engine solid mounted as well, plus a LOT more torque.

 

The original design of the 54-64 (65?) trucks has engine mounts on the bellhousing and an engine mount on the timing cover. The F100's have one mounting point on the timing cover right on the center of the crossmember, and the bigger trucks have a beefier frame and two mounting points from the front, timing cover mount.

The cab of a F100 is mounted to the frame on rubber bushing on the front of the cab, but the back of the cab is hung from two pivoting arms. It seems obvious that the frame, engine and cab were designed to flex.

The bellhousing mounts are directly in line with the firewall. The firewall would serve as a stiffening element that would resist the torque of the engine. By moving the engine mounts forward to the frame rails along side the engine, this stiffened design is lost. The frame is flexible and not actually designed to bear the weight and torque of the engine.

When you put a load on the engine, it will tend to twist the frame and raise one wheel (driver side) off the ground. In reverse, when you take you foot off the gas, the reverse load will tend to plant the driver side wheel and unload the passenger side wheel. If you're going down a hill this could get a little dicy.

The original engines in these trucks are deep-skirted engines. Heavy buggers, but stiff blocks that seem to serve as an element of the chassis design. Ford Y-block, Lincoln Y-blocks, FE, and the 223 all have this heavy, deep skirt design. And there are bellhousings with engine mounts for these engines.

I don't think the lighter Windsor, Cleveland/Midland or Lima designs would work as well in this type of configuration where the engine is used as a frame/chassis element. And I only know of one possible bellhousing, used for one year, that might fit the Windsor/Cleveland block.

What's my short answer? Take it easy with that 400. That's not an optimal lash-up.

If you want to try to return to the original engine mounting configuration, and are wanting a larger engine, consider using the FE bellhousing to mount an FE or early MEL. Engine sizes range from 330 to 462. A 360 or 390 FE would work great and they're easy to find.

 

oh yea this is for a 52' f2... and it has new location for the motor mounts. and thanks a bunch pcmenten

 

I'd expect my two new tubular crossmembers, one for the engine mounts and one for the transmission bolted to the frame adds much more stiffness than the original engine on 3 point rubber mounts ever provided. In fact the center front mount would allow the engine and frame to twist. Still think it's a non issue tho, work vehicles used ladder frames with the ability to twist if needed because it was expected they would be driven on very rough terrain with a 1/2, 3/4 0r full ton of load in the bed. Unless you're going off-roading or hauling gravel I don't think you'll get much or any twist on the highway.

 

What have you done to the 400 to get 350 horses out of it? I've got one I'm gathering parts for. Just about ready for block machine work. [psst.....no 'm' - makes ya sound like a bowtie guy ]

Stock form after '71 was 162 HP i believe on the smogged engine.

I agree with the consensus, I doubt you'll have issues with frame twist especially with the F2 frame.

 

Paul

That was a very interesting take. I wonder if you are giving the engineers a bit too much credit. If intentional, their plan to allow things to flex around was perhaps a failure. Body panel alignment is a nightmare. And the trucks don't handle too well either. I can see the intentional up and down movement of the frame as a potential advantage in load situations......maybe ...... but that's about it. The rest can potentially be improved IMO. They served their well purpose in the pre-interstate era.

 

There may have been some intentional end to end flex built into the frame, but I doubt it. I suspect it was unintended and the cause of the common frame crack. Twist is another story tho, you have a truck with two solid axles both suspended with leaf springs. Leaf springs have a fairly short working range, i.e. how far they can move up and down from their at rest position, so I couls see the chassis engineers seeing a loaded truck being driven across a farmers field or at a construction site (paved driveways were uncommon even in the city, dirt roads were the norm in rural areas in the 50's) where one wheel could drop in a hole or over a bump that exceeded that working range so the chassis was allowed to twist rather than bend permanently. Remember in the 50's a pickup was strictly a utilitarian vehicle, no one bought one to drive around town because they were "cool" or the fad vehicle of the moment, and as such were built for an expected hard life. The mere fact that so many have survived is a testement to the sucess of that design philosophy.

 

Dewayne, From what I've read, Ford has been designing frame twist into vehicle chassis' at least since the Model A. In the case of the 54-56 (and others?) F100, it seems pretty clear that they allowed for a lot of twist. Look at the rear of the cab of your 54 and try to figure out why they would suspend the cab with those hangers. It seems clear to me that frame flex is an integral part of the F100 design.

Right now, my 54 F100 does not have an engine in it. I'll try jacking up one front corner to see what happens - how much the frame twists before the other wheel comes off the ground.

My wife also has a 53 Studebaker half ton pickup and its frame is a massive boxed affair. I don't have any qualms about the idea of installing a Chrysler hemi in that little beauty. But it is definitely a heavier vehicle. The F100 is a lightweight vehicle by design.

BTW, I've heard people describe the 223 6 cylinder as a 'heavy' block. It's not particularly heavy. I can lift the bare block into the back of my truck or lift it off the engine stand and set it down on the floor. But it does have a deep skirt and a cast-in lifter chamber.

The Y-block may be a bit heavier than a 302 or 351, but it is a rigid design and it seems to be part of the 'structure' of a F100. A Y-block has a deep skirt and a cast-in lifter chamber. A solid looking, stiff block.

I've heard that in racing applications like NASCAR, the builders use plates bolted to the front and rear of the block to mount the engine. The side mounts distort the block when the chassis flexes. I'll bet that's an issue when you put a weenie Windsor in a F100.

 

In my first 1960 ford truck I ran an olds 455 with 3.25 gears and would leave a strip of rubber thru first and second gears, then being a high school kid I had no money for gas or tires so it was replaced with a 350 olds that was later modified with cam, intake, carb, headers and never had frame twist. My cousin was mad because I always beat him at the drags(against his 74 toyota truck-4 banger) so he installed an early 289 cobra motor with a supercharger and NOS to get it down the track in the low 13's-high 12's tires spinning most of the way and still no fram twist


I think you will be fine without having to box the frame

Glack

 

thanks... i also remebered the guy with the dart kept on braking motor mount so he put in solid mount..... the one reason for so much twist

 

Paul, Dewayne,

Great discussion about frame basics for these trucks.

I can tell you from first-hand expeirence that the stock frame - even on my F-250, is not designed to resist out-of-plane flex, except in the end-to-end mode as AXracer mentioned. I had the bare frame restored with nothing attached, and you could easily pick up one corner and lift it a few inches before the adjacent corner came off the jack stand.

From an engineering standpoint, the shape of the frame members used, and the way they are fastened together, is clearly not intended to resist the flex (or twist) in the side-to-side mode. In fact, some of the crossmember joints with the frame rails are specifically designed NOT to stress the frame members when the frame twists. On the other hand, the frame is very stiff in-plane, and holds the axles and other components in place very well.

The designers of these trucks were smart people, and they understood the basics of automotive chassis design long before the 50's. For heavily loaded vehicles on very rough surfaces, trying to build a stiff frame that would successfully resist the twisting stress would have required some sort of frame members that were well out of the plane of the frame. Something like a dune-buggy or NASCAR chassis comes to mind.

Fenders is also right in that the flex makes these trucks handle somewhat poorly when compared to unibody or tubular frame vehicles. As Paul said, they were designed to get across plowed fields and muddy grain elevator yards, unlike newer vehicles. They didn't need to handle with that crispness you expect from a modern car where the frame/body flex is kept to a minimum and the suspension is designed to provide precise handling.

 

Paul and George,

After careful reading of your well written posts, (that and havin' me another look at ol' flexxy out in my garage), I will concede the point and live to debate another day.

Now whether it was such a wise engineering decision, I'm not yet convinced. It might have been a good idea at the time. So were 8 track tapes. We're going to debate that one on the suspension thread in a few days perhaps.

Good to have you back George! And sorry I tool so long to acknowledge your post Paul. This thread slipped off my radar. Finally got a break from work and really been hammering on the truck this long weekend.

 

Hey guys. there seem to be alot of talk about should he box or not. My feeling its better to be safe than sorry. It takes maybe $100 in material & about 4 hrs welding to make sure there is no problem. Glad I did it to my 56 with the 383 road runner engine in it. Besides I think it adds to the value of the truck.