Boxing a frame is done to provide additional resistance to end to end flex (think of a ladder laid between two saw horses. If you sit in the middle and bounce up and down that's end to end flex). It also helps resist twisting or spread of the individual rails. But with a ladder frame only adding additional structure such a deep profile K member or a rollcage structure will stop torsional twisting.

 

"adding additional structure such a deep profile K member or a rollcage structure will stop torsional twisting."

Not exactly what he is referring to I'm sure, but installation of the K member AKA Volare clip stops the frame twist cold. (Up front anyway)

PoolPro

I don't see a problem with boxing end to end, though I'm also not sure what advantage it offers. I haven't heard of any problems with stock frames catastrophically failing. Only serious documented problems frame issue I have ever seen were bad GM/LTD style clip installs. And also if you only box part of the frame on other type IFS installs. The point where you end the box plate is going to see some stress.

 

Boxing will not resolve the issue of frame twisting. Adding a crossmember that is fairly massive might reduce twist to a degree, but the entire chassis needs to be considered before resorting to something like that.

I have a Gibbon's Cordoba front-end conversion kit that has a hell-for-heavy crossmember that would probably help with the frame twisting (not yet installed). But when I do install it, I will probably box the frame to the front of cab, and convert the front motor mount to the F250 style mount.

Doing this will easily add about 200 lbs or more to the weight of the truck.

If I leave the truck with the stock I-beam front axle and use the original motor mounts, my truck would be lighter, quicker, get better mileage and probably be more durable. But it would steer, handle, and ride like a truck.

George, thanks for your comments. Light bulbs are going off in my head and I now understand the design of the Gibbons' crossmember.

The engine bellhousing and its engine mounts would make and 'out of the plane' (above) frame member. The Gibbons crossmember would make another, below the plane, frame member. The F250 front engine mount would make another, above the plane, frame member. I'm finally satisfied that I have a workable design for a stiffer, safer frame.

Seems like a Volare style front-end would also have this 'out-of-plane' advantage.

Regarding boxing; When the time comes, I'm going to look at the frame of an F250 to see if I can cut it up to box my F100. I'm hoping to close in the frame in a clamshell style, making a tube out of two 'C' cross section frames.

Welding fishplate onto the open side of the frame is not a good way to go. The welds end up right on the axis of stress and they become a weak point.

 

I have a 375 hp 440 in my 54 f-100 and i did not have any problems, so my guess would be that you should be fine although boxing would be best. Also your are comparing 350 hp to about.... and i'm only guessing 800 hp ? with the blown 426 man ! i get the chills just thinking about that kind of hp !

 

yea.. im sure i will be doing some major chassis design before i drop the 460... but thats way down the line, the 400 is plenty beefy for right now without major changes, and i also decided to stroke the 460, i remeber seeing a kit the gets it to 492, or somewhere around that range..

 

Your clamshell idea will make a frame strong enough for a tank, and nearly as heavy.
The proper way to box a frame is to cut your fishplate (typically 10 ga cold rolled) the width of the INSIDE of the top and bottom plates, taper grind the edges then set the plates 1/16" inside the frame, tack ~ every 6" then fill weld between tacks alternating front rear top bottom of both rails to minimize distortion. when you are done, grind the welds flush with the fishplate. You will have frame rails that will never bend.
after boxing be sure to weld in tubes for any thru bolts so you don't crush it in.
A thinner rectangular shape tube on edge is stronger than a square tube of the same height.

 

AX

What you decribed is pretty much standard accepted boxing procedure. Prior to your arival to the forum, we had more than one discussion on the transition from boxed to non-boxed. Most of us are just boxed in the front, and most of us are experiencing no problems. But there have been some trucks crack where the boxing stops near the firewall. Especially on the trucks where the stock frame is completly chiopped off. AKA Camaro clip job.

Several of the clip styles Volare, Camaro, LTD and some others just make the front of the truck incredibly strong. We have often wondered if the rear should be reinforced to match. Have you seen a Volare install? The Volare K member sits behind the stock Effie front crossmember. It transitions the front of the truck into extreme crossmember overkill. Just under 2 feet of crossmember, and then nothing else until the transmission crossmember at least 3 feet back. Just bringing you up to speed on our past conversations. I really have no point to make here.

 

For what it's worth, my 56 is pushing 450HP at the rear wheels with a big block you-know-what...has been for about 10,000 miles. The motor mount is a u-shaped saddle type bolted to the front of the engine sitting on channel shaped brackets bolted to the frame. A bolt/rubber doodad (love that description ?) fastens it together. The trans mount, which supports a heavy TH400 w/ GearVendors overdrive setup rests on a simple fabricated piece of angle iron bolted to the frame.

The frame is not boxed anywhere. Presently, I have the whole front apart down to the frame in a major detailing effort. It's pretty easy to see everything...there appears to be no problems with cracking, flexing or twisting. I waited to post in this thread until I checked thoroughly; thought I should check for potential problems. I'd say these stock frames were built dang tough!

Now here's a real kicker: The previous owner had a blown big block in the truck for a while back in the mid 80's...same mounting setup. That engine topped 750HP! The truck did a quarter run at 9.5 and 145. If that frame was going to twist, it would have done it then.

Moral of the story?...put whatever you want in there and don't worry if the frame is stock. Once you start grafting, well...who knows?
Norb

 

Grafts should always be doubled up with fish plates. They are called that because of their "peculiar" shape, a deep U cut into both ends like a fish's tail or mouth so the weld is NOT in a vertical straight line. Either the inside or outside plate should extend at least 6" beyond the one on the other side of the splice. The splice itself should be cut on the diagonal rather than vertical and finally the fame should be boxed with fish plates ~ 3' long. The other way is to reinforce the splice with a 2' section of rectangular tubing that is a tight fit inside the frame rails and plug welded several times thru each flange and the side of the frame. I prefer the fishplate method for strength and appearance.
Some builders use a long diamond shaped doubler (a kind of reversed fish plate)on the outside because they like the appearance better.

 

its been very intersting to hear whats been said, ive done alot of reading to learn most but have no hands on.... mostly because i have to do my work in the driveway, so no shop to work in. ive always told myself the best way to learn is do it yourself, if you cant, then find someone who has.

 

One more moral to the story. I don't care if you swap in a Moped engine. It's not factory, you did no extensive R&D, so it just makes good sense to keep an eye on ANY frame, brake mods etc. It takes about 2 minutes to look things over while you're changing the oil. Make sure you aren't developing a new crack, chafing a brake line or what have you.