Targa/Cab Strengthening Idea

[Shaun @ Tru6]

So I've got this rusty 70 targa that I'm cutting up and making into a no-frills little speedster including doors welded shut. The driver's floor is bad and will need replacement, a big job but very doable.

As I was looking at the car today, I got to thinking about how to strenthen the tub. Part of my plan is to put a cage into. But if I weren't, what would I do.

I had the idea that I could pull the entire floor pan out and weld in flat sheet stock. Then I could fit in some 1.5 inch thick aluminum core honeycomb sheet wtih plenty of structural adhesive. Then put a layer of steel on top of that bonded in and tacked all around the perimeter, maybe coming even with the center tunnel.

Thoughts on this? Will it work? To what degree if any?

[mjshira]

I think that is a lot of work and could add a lot of lbs. Recommend you consider sending tyson and email. He did my car and it is really like driving a coupe without a cage...

good luck.

[Shaun @ Tru6]

Thanks James, looking forward to learning anything I can from Tyson.

[tctnd]

If you are really serious about welding the doors shut, a beam across the top of each opening and an x-brace will stiffen it more than anything you can do with the floor. These bits will need to be properly fabricated; just welding a piece of pipe across the jams won't cut it. Then take the skins off the doors and weld them directly to the body.
regards,
Phil

[Matt-Man]

Hey Shaun, something I have been considering for my own Targa is to run a brace from a roll bar (if I end up with one) or from the seat belt shoulder mount bolt (like the Targa brace they sell), but rather than bolt to the lower seat belt mount, run the brace all the way to the front of the side of the seat mount area. I'm thinking as far forward as possible dictated by the height of the side of the seat and tying in to the heavy flat area where the seat rails bolt in.
In your case with the doors welded shut, you could go all the way to the front footwell and lower dash area effectively triangulating the door area. Might as well connect to the front strut tower too! Seems like it would be the next best thing to a full cage...

Matt

[Shaun @ Tru6]

Thanks Phil, good ideas on welding the doors shut. I was also going to weld the inner bottom of the door to the sill with something in between. Perhaps I'll just do a rollhoop and less of a cage. We'll see.

Also good ideas Matt, thanks.

I've got more work than I can shake a stick at through January 15, after that I'll get this thing on a jig and start to map out some configurations with PVC and post accordingly.

Until then it's just clean-up and protection work.

[Wrecked944]

Hey Shaun, I know you have seen the long running thread about chassis reinforcement. But Walt Fricke just added this interesting tidbit...

Originally posted by Walt Fricke
Ludvigsen, p1381:

"Finite-element modeling (FEM) was vital to tha comprehension of the structure that saved materials and weight while at the same time increasing the body's torsional stiffness by more than 30 percent over the 993; the FEM computer model of the 996 body had a staggering 180,000 separate analysis elements. An important conribution to strength was made by bonded-in front and rear glazing, which accounted for 21 percent of the torsional stiffness increase. Making a similar contribution were the underbody diagonals that bridged the baps in the cody where the suspension subframes were inserted. The complete body's torsional stiffness was 14,800 lb-ft per degree of twist."

I have no clue what "rear glazing" and "underbody diagonals" mean. But the latter sounds vaguely related to what you are planning to do. I asked for more detials in the original thread. Here it is for reference...

Structural Reinforcement

[Matt-Man]

"bonded-in front and rear glazing" is in the same as saying "glued-in glass"

Matt

[John Kelly]

You will be amazed at how much welding the doors to the body will stiffen up your car. For the best possible outcome on the outer skin, make a strip of metal at least 2" wide that covers the door gaps, scribe and cut away the metal beneath and flush (butt) weld the new metal in. This will allow you to do metal-finishing to whatever level you can, and reduce filler shrinkage at the gaps which can be a problem if you simply weld the gaps. I learned this the hard way doing the Ghia roadster on my web site.

John www.ghiaspecialties.com

[randywebb]

Check out the thread titled Structural Reinforcement.

Some intersting 'hidden' things to do are:
1. add the cab floor bracing if not already in your targa,
2. add sheet metal along the outer rocker areas
3. seam weld all the area that are now spot welded
4. cut out a 964 tunnel and weld it in right on top of the existing tunnel

there are other ideas in the thread I referenced - the idea was what could you do if you did NOT add a roll bar or cage - i.e. for a street car.

[safe]

Originally posted by Shaun 84 Targa
So I've got this rusty 70 targa that I'm cutting up and making into a no-frills little speedster including doors welded shut.

With the doors welded shut properly the car must become way stiffer than a coupe.

[Joeaksa]

Shaun,

Speaking from experience, until you cut out all of the rust, its going to continue. You might think about cutting the old out and putting a new floorpan on the car instead of leaving any of the old metal in.

I lost a '72 model to rust overseas and its a sad event so hope you can save the car for good.

Joe

[KobaltBlau]

Shaun,

To your idea about aluminum honeycomb, it is an interesting idea. Properly bonded honeycomb sandwiches (usually fiberglass panels top and bottom) are extremely stiff at least in beam, I don't know much about the torsional stiffness but believe it is also very high. I think the problem would be attaching it to the stamped steel unibody in a way that would be durable and not deflect at the joint, losing the benefit. you might end up building a complete structure from front suspension mounts to rear, which probably isn't the goal of an exercise that tries to keep a cab or targa accessible.

[Shaun @ Tru6]

Originally posted by John Kelly
You will be amazed at how much welding the doors to the body will stiffen up your car. For the best possible outcome on the outer skin, make a strip of metal at least 2" wide that covers the door gaps, scribe and cut away the metal beneath and flush (butt) weld the new metal in. This will allow you to do metal-finishing to whatever level you can, and reduce filler shrinkage at the gaps which can be a problem if you simply weld the gaps. I learned this the hard way doing the Ghia roadster on my web site.

John www.ghiaspecialties.com

John, that is truly outstanding work! Thank you for the link and how-to on welding these shut. Really looking forward to it now. Damn work keeps getting in the way of fun.

Hope to post in late January-February, which probably means March.

[Shaun @ Tru6]

Originally posted by randywebb
Check out the thread titled Structural Reinforcement.

Some intersting 'hidden' things to do are:
1. add the cab floor bracing if not already in your targa,
2. add sheet metal along the outer rocker areas
3. seam weld all the area that are now spot welded
4. cut out a 964 tunnel and weld it in right on top of the existing tunnel

there are other ideas in the thread I referenced - the idea was what could you do if you did NOT add a roll bar or cage - i.e. for a street car.

thanks Randy. I'm definitely adding the cab bracing and have plans on seam welding the tunnel, just for prcatice if nothing else. with the doors shut, I only need to think about a roll hoop for safety since the windshield is gone. Will either go with a single bar or get fancy with an M design with stays going from the top of the arches back to the motor bay rails.

Clearly too much time to think, to little time to do.