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Discussion Starter #1
I'm planning on doing quite a bit of structural improvements to my '65 Fastback. Below is a list of what I've planned at this point.

I'm not interested in a 6 or 8 point cage as the car will be 90% street and only 10% on track (i.e., HPDE, hot laps @ Willow). Plus I need to retain use of the rear seats for now (but can pull out on track days).

Also I've elected to not install the convertible rockers.

The car is also getting a 347 stroker engine with at least 450+ h.p. (similar torque) running through a Toploader 4 speed and 9" rear end with either a panhard bar (Maier Racing or OTR) or a Watts Link (S&T or OTR).

All of this is to handle the horsepower, improve the handling, and make the unibody somewhat more modern in terms of rigidity.

Here's the overall plan...welding starts this week:
  • Export Brace: stock OEM Ford stamping with extra CJPP firewall L bracing welded @ underside of brace mount points on firewall (yes I know they were installed by Shelby on topside...not sure how topside is stronger)

  • Monte Carlo Bar: straight bar from Street or Track (made from thicker walled tube)

  • Strut Bar: USCT strut rod C channel reinforcement plates welded @ front of C channel

  • Extra Welds: top side of the strut rod C channel @ front cross member and @ front sway-bar mounting bracket

  • Shock Towers: outside lower Trans-Am style stiffening plates welded @ full perimeter (plate welds in the "trough" at bottom up to just below the UCA mounting points for the Shelby/Arning drop)

  • Front Frame Rails: welded additional frame rail exterior plates right below and slightly wider than shock tower area to reinforce front frame extensions

  • Lower Cross Member: Z-Ray / OTR street competition lower cross member bolted in

  • Roll Bar: 4 pt roll bar (welded @ floor on top of rear torque boxes & extensions welded @ rear wheel wells); it is also bolted-in at the top of the roof line (where the 3 point belt bolts in)

  • Front Torque Boxes: 1967-70 OEM Ford style (Dynacorn) two-piece torque boxes with the extra 3rd piece corner gusset (removed the brake cable tube from passenger side box)

  • Rear Torque Plates: USCT rear convertible torque box plates (welded right over rear torque boxes)

  • Convertible Seat Pan: Dynacorn version made for Coupes and Fastbacks without the Convertible rockers...stitch welded around the perimeter of pan to floors, inner rockers, and transmission tunnel

  • Floor Pans: 1/8" x 1.25" flat steel welded to bottom of floor pan (exactly where front and rear spot welds for seat interior pans are located); plug welded from top through original OEM spot weld holes with some stitch welds on bottom side too; runs ~5" up the inside of transmission tunnel

  • Rear Seat / Dual Exhaust Pans: both rear floor pans stitch welded around perimeter of pans (intended for dual exhaust...but using to strengthen floor and add secure mounting points for rear lap belts)

  • Sub Frame Connectors: Spin Tech SFCs welded from front frame rails (cups over the floor pan supports)...along the floor pans...back to the rear frame rail...and around the rear leaf mounting bolt

  • Rear-End: Tank Armor (11 gauge plate steel cover that sits over fuel tank); mounting bolt points for the gas tank to unibody will be reinforced with 1/8" x 1" flat steel tack welded from bottom-side and bolted together with Grade 5 fasteners; all this ties together the rear end...adds needed weight to the rear end...makes me feel a little better about 22 gallons of fuel out back having some protection (may later add a fuel cell but not at this point)
Some of the above is probably overkill.

Anything else I should consider, like stitch-welding floor sections or firewall? Coupes typically also install a sheet of metal behind the rear seat...but this is a Fastback...never seen anyone weld a sheet over the trapdoor opening.

Thanks in advance. Photos appreciated for any additional ideas.
 

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WOW! Sounds like you pretty well covered it and more. The only thing beyond that I went with is small braces to add a little triangulation at the area right in the corner between the front frame rails and the torque boxes. The export brace and monte carlo bar strengthens on the inside of engine bay, this just adds a little stability on the outside. Probably over kill but doesn't take long to do.
 

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Discussion Starter #3
Thanks @Huntingky. Are you referring to this triangulated part? (piece w/ the drain hole in it) It's referred to as the "torque box gusset".

755273


If so, yes I have that part...it comes with the late '67-'70 torque boxes. Exactly why I ordered the later year style boxes.
 

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Thanks @Huntingky. Are you referring to this triangulated part? (piece w/ the drain hole in it) It's referred to as the "torque box gusset".

View attachment 755273

If so, yes I have that part...it comes with the late '67-'70 torque boxes. Exactly why I ordered the later year style boxes.
Yep, GUSSET.....I am very bad about getting sudden brain farts and forgetting the names of parts......friends.....one day I will screw up and it will be my wife's name...haha.
My 65 didn't come with gussets, made my own.
 

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Looks like a great list.

When I installed the Spintech sub-frame connectors, at the point where they slip over the front frame rail, they weren't tall enough to meet up to the floor. I wound up cutting off the lip and plug welding them to the sides of the frame rail. You'd have to modify them if you wanted to weld them to the underside of the floor too. I don't think just welding them to the frame rails impacts their strength...they are welded to the floor between the frame rails.

I had to use sheet metal screws to pull them up to the floor before welding. Screw in down into the frame rail to pull it up to the floor. If you screw them up to the floor from under the car, the screw will strip out the hole since the floor sheet metal is thinner (I know that from experience).
 

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Discussion Starter #7
While finishing up the removal of all undercoating I had two surprises lurking...

The DRIVER floor support cracked halfway between where it’s welded to the front frame rail and the transmission mount.

The crack goes down the right side and wraps under to where an existing drain hole is located. So ~1/3 of the of the U shaped support. Was covered in OEM undercoating and no one has ever seen it.

It did not crack all the way to the top of the floor support (where meets the floor).

It’s a really rust free car and the insides of the floor supports are nice (I cut the ends off to look inside). So it’s definitely not a rust issue.

BUT that’s not all...

More undercoating cleaning off the PASSENGER side floor support revealed a 5” patch (same location as crack on opposite side). Looks like someone took another floor support and seam welded a 5” section from a 2nd floor support all around the original support. Not sure what’s under the patch but again it’s not rust. Then they sprayed a bunch of undercoating all over it.

Tells me the car had a front end hit at some point over it’s life. It must have bent or cracked the passenger floor support and they repaired it. But no one ever checked or found the driver side damage.

Thinking that I leave the passenger side repair alone...it’s held for years.

Then on driver side drill a pinhole at the end of the crack and seam weld flat plates on side and bottom (how long?) spanning over the crack.

These areas will be completely covered by the Spin Tech subframe connectors which are welded over the floor supports AND then torque boxes are welded to this area and flat across the bottom of the floor support too.

I’m not looking for an original appearing underside - just a solid/strong structure. Seems like a ton of work to completely drill out 52 spot welds per side and completely replace both floor supports. Only to have them covered up by the subframe connectors and torque boxes.

Thoughts?
 

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only thing i really see is you adding the flat stock steel to the floor and around the gas tank is kind of like adding weight for little benefit. the flat stock is not going to add much stiffness. you would be much better off using 1'' square tube around the gas tank mount lip. that is exactly the same as i am doing. tubing will add both crash protection and torsional stiffness. the flat stock will not add much of either.
 

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I'm with bikefreak, I would stick to fixing areas that fail under hard use, no sense in adding weight fixing a problem that doesn't exist especially when you consider that we move a 40# battery "for weight" to the trunk. Heck, I'm considering dumping a good 400hp 351 for a 400hp 347 just to buy 70 lbs of weight on the front end to make it turn in better. Not that I'll really do it but i fanticize about buying a Fox with the right motor and swapping then sell the Fox...
 

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The sun frame connectors are a tight fit around the frame rail, so not sure you can put a plate on top of the crack. Maybe just drill the ends and put some spot welds to help stop if from growing.

Plug welds on the sides of the sub frame connector will lock everything in place and prevent the cracks from growing.


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Discussion Starter #12
Thanks for above suggestions. Don’t want to add any weight unless I’m getting benefit from it.

Will scratch the flat steel on bottom of the floors off the list.

And will change the gas tank mounting flange to 1” steel tube.

I’m probably overthinking the crack in the floor support. Just was alarming to find both issues. Good idea to use the subframe connector as a patch with plug welds around the cracked area in addition to welding up the crack.

Met with my welding / fab guy today to go over everything (welding tomorrow), and he’s good with the plan except welding in the subframe connectors at this point.

The engine is out (being built) and he prefers to have the weight of the engine in the car when he welds in the SFCs. He’s done a lot of race car fabrication work, so I guess we will install the SFCs later...
 
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