Fold down rear seat vs body stiffness

[metallidart]

My 1973 Dart Sport 340 is the planned home for my W2 headed 422 if I ever get it done. The car is pretty much rust free, mostly original (but shot, and wearing the ugliest stripes in the history of cars). I already added a tubular radiator support, and torque boxes, subframe connectors, firewall to inner fender/shock tower reinforcements, and some other little odds and ends will be installed before the stroker.

I was poking around on the web, and came across a post on a forum saying the fold-down rear seat cars were a poor choice for racing or performance handling because of the lack of the "x" brace behind the rear seat. I thought about that before, and I assumed that the engineers would have added bracing to make up for it. I haven't removed anything for a look, yet.

I don't have plans for a cage, yet. Maybe down the road.
What say ye? Is it a lost cause without adding an x-brace? Or will the mods I have planned be enough? Any experience?

 

[metallidart]

Side note: I won't have sticky tires for a while, probably 17" with tires to make it handle. Down the road I would like to make it a 5 or 6 speed. Waay down the road.

 

[72bluNblu]

First of all, with all the chassis work you've done already I'd say you're already light years ahead of any stock non-fold down car. Which makes all of the rest of this fairly didactic, but since I have a bunch of research I'll share anyway. ;-)

Fold down seat cars do have some additional reinforcing to help make up for the removal of the X brace. There are a couple of braces on the floor that connect the wheel tubs to the floor. And then there's the rear panel itself. Although the package shelf is shortened, its also reinforced with multiple layers around the edge, and the braces that tie it to the wheel tubs are stamped, multi-dimensional pieces compared to the plain flat braces in the non-fold down cars. The package tray on the non-fold down cars is just a single sheet, no multiple layers around the edge.

The x-brace itself isn't all that spectacular either. The whole thing is held in by 18 spot welds. I may know that for a reason.

Here's some pictures of my original non-fold down Duster. As you can see, other than the X brace, the package tray isn't reinforced all that well.

This one tips my hand a bit. Here you can see the lower panel braces from a fold down car in my Duster. As well as an upper reinforcing bar.

And here are some shots of the package tray from an original fold down car. You can see the reinforced edge of the package tray and improved braces for the wheel houses.

Then there's the rather large panel that the fold down cars get that covers the axle hump, covers the floor braces, and makes everything nice and even with the rear seat and rear panel. It's held down by 11 sheet metal screws, which make it about as well attached as the original X brace. It might serve the purpose of giving a nice flat pass through, but it also reinforces the area.

So, I wouldn't worry too much about the lack of an X brace causing you chassis issues. The engineers DID reinforce the design to make up for the missing X brace. I can't say positively that one is stronger than the other, but I would guess that the fold down cars had to meet the same standard as the non-fold down cars. In fact, the later cars (when the fold down seat started) had to meet higher standards than the earlier ones, which is why door bars and other crash protection items were added. The X brace is easy to visualize, but a lot went into designing the reinforcements for the fold down seat area. There's certainly more metal in the fold down cars, its not a weight saving item compared to the X-brace and standard seat.

 

[metallidart]

Awesome!! I really, really appreciate the info. Honestly, it almost looks like the fold-down cars may be stronger, with all the extra bracing. I'm not too worried about it now after seeing your pictures. I was honestly contemplating selling the car.

I may, once I get the plastic peices off, see if I can add anything that will be hidden once its all back together.

Once again, I really appreciate it!

Now, I will look at your pics and see how far I can move the wheelwells in....

 

[metallidart]

Looking at the pics, I'm already getting some ideas!

 

[airgrabber]

If you do move the wheel wells you will probably have to give up the rear folding seat, unless you want to do major surgery on the seat back and the related components. It may be also be a pain to get the latches that attach to the wheel tubs to line back up so they function properly. You would probably be cutting into that extra bracing in order to move the tubs in, or at least popping the spot welds for the bracing.
I moved the tubs in on a 71 Demon and got 2 1/2 - 3 inches on each side. This is not an exact science since the factory had some leeway when hanging the original sheet metal, and difference of 1/2 to 1/4 inch are not uncommon. All that seam sealer hides a multitude of gaps.
If you are set on doing the mini tub it might be better to remove the latches, narrow and remount the seat top, and then when the tubs and seat are in, remount the latches in the position that will make them line up and work, and that might not necessarily be in their original mounting holes. If you move the latches, your finish panels might not line up in their original holes - may have to open them up.
There's also the new space opened up by adding the metal to widen the tubs that won't be covered by the finish panels.

 

[metallidart]

I was wondering about that. I haven't really looked at the latches yet, but everything you said makes sense. Maybe I will just do the offset hanger deal and take advantage of the extra room from that and leave the rest alone.

 

[72bluNblu]

A mini tub on a fold down car would be a little interesting. I actually think the rear seat would be the easiest part of it, the brackets that locate the rear seat are basically "flush" with the outside of the wheel house. You'd have to make new mounts, but I think the seat could actually stay in the same place. As far as the seat mounting brackets and latches, they're easy. If it isn't totally obvious from my pictures, I converted my standard Duster to a fold down seat. Locating the mounts and latches isn't all that bad since you know where the seat goes.

But the pass through panel would have to be cut down, the reinforcing panels moved, the and the rear fold down panel would have to be cut down.The finish panels wouldn't fit at all, you'd either have to cut off the section that's visible next to the fold down seat or ditch them entirely. And the end result would be a pass through area that would be really small- not all that useful. It'd be a lot of work, and after all of it the advantage of having the fold down seat would pretty much be gone.

With a Duster you can run 275 wide tires without moving anything with the proper backspace. I test fit a set of 275/40/17's on my Duster on a set of 17x9's with about 4.75" of backspace, stock axle and spring location. They were tight, but they would work. With a set of offset hangers/shackles I'd bet you could fit a 285 wide tire. Keep in mind that's for a lowered car, with the wheels entirely within the wheel wells.

 

[805moparkid]

BO29 Cuda... nough said

 

[autoxcuda]

BO29 Cuda... nough said

They had cages and were intended to have cages.

I asked Bob Tarrozzi why they didn't pick a 68 Barracuda notchback. He said he was told which cars to do. He figures the fastback was picked for marketability as it was a sportier "look".

There's always a controversy between SS Dart vs. SS Barracuda for what's the best car with all kinds of arguements and points.

the fastback folding rear seat and mechanisms weigh more than a coupe rear seat. Of course that doesn't matter for a 68 SS car and they removed the rear seat anyways.

When they first started SCCA Trans Am, Ford choose Notchback Mustangs from 66-68. Even though Shelby was the factory sponsored team and they sold Shelby Mustang Fastbacks.

The 64 and 65 Hemi Super Stock were post cars. It's generally accepted post cars are stiffer. Probably very minor, but stiffer.