To box rear frame rails or not?

[VicsGarage]

So I'm in the midst of my restomod / restoration and wanted some opinions on rear rail boxing.

Was wondering it its worth while?

My build thread is here 1971 Dodge Charger SE restoration.

I got to post some updates but front rails are in, front floor is mostly welded in and rear rails are on the front are set looking good. Might need a bit of tweaking at back, but almost done with that stuff.

Before I put my rear seat pan in, I was wondering it it would be worthwhile to box my rear rails in. I have a pretty mild 440 right now that is low compression. I'll likely end up supercharging it I'm thinking. Would boxing the top of the rails add a lot of strength? Would it be worth it? Or would it be overkill? Was wondering what others think.

 

[70chall440]

Well it isn't going to hurt anything but IMO it is not overly beneficial given that the floor pan is spot welded on top of the rails essentially boxing them in. I would recommend being generous with the spot welds everywhere you can to include along/across any seams in the floor pans.

If you want a stiff car that promotes handling and braking then install subframe connectors and torque boxes at a minimum. You can also install under fender braces, lower frame supports and lower radiator core support, additionally you can add an engine brace from XV Racing.

 

[Matthew J]

What 70chall440 said

 

[dvw]

What do mean by boxing them? Like Hemi/convertible torque boxes? Unless your worried about a stock resto I'd put subframe connectors in it.
Doug

 

[ckessel]

I'm also down for adding welds in. Easy to do, just takes time. Get yourself a Rota Broach set from Blair, covers 1/4-3/4" or they have actual spot weld drills for use on removing old welds. If you look at the factory weld pattern, you could easily add 1-3 more welds in between which makes a huge difference in the stiffness. I did this too when I put my SFC's in. They got sleeved into the existing rails, slit the rails to pull them tight against the SFC's after cutting holes in the rails for welds, welded them up. Also the SFC's were extended so I could weld the USCT spring relocation unit to them along with the rails. On my k-frame, did similar there too. I added 120+ welds on the k. Factory amount was 30 or so.

 

[VicsGarage]

What do mean by boxing them? Like Hemi/convertible torque boxes? Unless your worried about a stock resto I'd put subframe connectors in it.
Doug

It would be welding a plate along the top of the rails. It would look as if they're a square tube vs U shape.

 

[VicsGarage]

Well it isn't going to hurt anything but IMO it is not overly beneficial given that the floor pan is spot welded on top of the rails essentially boxing them in. I would recommend being generous with the spot welds everywhere you can to include along/across any seams in the floor pans.

If you want a stiff car that promotes handling and braking then install subframe connectors and torque boxes at a minimum. You can also install under fender braces, lower frame supports and lower radiator core support, additionally you can add an engine brace from XV Racing.

Valid point...

I plan to use the whole kit from American Car Tool I think it is?

 

[Bighouse]

It would be welding a plate along the top of the rails. It would look as if they're a square tube vs U shape.

When you weld the floor to the rails that creates a tube.

 

[hunt2elk]

Valid point...

I plan to use the whole kit from American Car Tool I think it is?

US Cartool. One interesting thing that I learned when talking to the owner. They spent a lot of time testing a B-body on some kind of machine checking for body flex. He said frame connectors and torque boxes are the most beneficial. I did also use their inner fender braces. Was asking him if the lower radiator support was worth installing. For a hot street car, he said not really. But he said one thing that really stopped a lot of body flex was to weld the firewall to floorpan seam solid. I did do that as well per his recommendation.

 

[eldubb440]

all of the above......... that being said; if you are hell bent on doing it, it certainly won't hurt anything and is a pretty simple operation.

my opinion is these cars take hundreds, sometimes thousands of hours to build. I try to concentrate my efforts on things that actually matter. Too much overkill is a major contributing factor to why it can take so long

 

[Michael_]

If you want a stiff car that promotes handling and braking then install subframe connectors and torque boxes at a minimum. You can also install under fender braces, lower frame supports and lower radiator core support, additionally you can add an engine brace from XV Racing.

Or you can go even further and swap a full frame chassis from schwartz performance or roadster shop under there...

 

[VicsGarage]

US Cartool. One interesting thing that I learned when talking to the owner. They spent a lot of time testing a B-body on some kind of machine checking for body flex. He said frame connectors and torque boxes are the most beneficial. I did also use their inner fender braces. Was asking him if the lower radiator support was worth installing. For a hot street car, he said not really. But he said one thing that really stopped a lot of body flex was to weld the firewall to floorpan seam solid. I did do that as well per his recommendation.

Really? I’m assuming from the inside of the car?

 

[hunt2elk]

Really? I’m assuming from the inside of the car?

Yes.

 

[dvw]

It would be welding a plate along the top of the rails. It would look as if they're a square tube vs U shape.

The only place I did that on my 64 is where the cage bars land on top of the rear shock mount. And where the outrigger tubes land against the rocker for the cage. The rest of the rear rail and front rails are factory. The ladder bar suspension attatches to the stock frame rail as do the subframe connectors and the rear upper shock moubr bar. It works very well. Car doesn't seem to flex. Hasn't cracked anything, bent the 1/4s. The body is still laser straight and the doors open and close like new. This has been beat on for 10 years well over 800 passes. I would say boxing isn't necesary. I can tell you I've had a 64 Fury H/T on the hoist with no frame connectors. The doors open poorly when on the hoist. I'm doing a Duster right now. Subframe connectors, no cage. Doors open perfect on the ground or on the hoist.
Doug

 

[Superfreak]

Or you can go even further and swap a full frame chassis from schwartz performance or roadster shop under there...

The Schwartz setup can easily turn into a $20,000-$25,000 affair.

 

[Curiousyellow71]

The only place I did that on my 64 is where the cage bars land on top of the rear shock mount. And where the outrigger tubes land against the rocker for the cage. The rest of the rear rail and front rails are factory. The ladder bar suspension attatches to the stock frame rail as do the subframe connectors and the rear upper shock moubr bar. It works very well. Car doesn't seem to flex. Hasn't cracked anything, bent the 1/4s. The body is still laser straight and the doors open and close like new. This has been beat on for 10 years well over 800 passes. I would say boxing isn't necesary. I can tell you I've had a 64 Fury H/T on the hoist with no frame connectors. The doors open poorly when on the hoist. I'm doing a Duster right now. Subframe connectors, no cage. Doors open perfect on the ground or on the hoist.
Doug

View attachment 1390463

Got any pictures of your ladder bars? Curious to how it fit with stock rear frame rails. Excellent looking frame connectors! Is this the full box cut into the floor, or welded to the bottom of the floor? The welding is so clean it's hard to tell?

 

[dvw]

Got any pictures of your ladder bars? Curious to how it fit with stock rear frame rails. Excellent looking frame connectors! Is this the full box cut into the floor, or welded to the bottom of the floor? The welding is so clean it's hard to tell?

Here you go back 12 years before sandblasting was finished.
Doug

 

[HEMIB]

I used the USCT frame connectors ,torque boxes & front radiator support cant see a lot of sense on the inner guard connectors all that structure only to end up being welded to the sheet metal firewall