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Discussion Starter · #1 · (Edited)
I'm planning on doing quite a bit of structural improvements to the unibody on 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 (can pull rear seat out seat on track days).

Also I've elected to not install the convertible rockers as my floor pans are in excellent condition and I feel the convertible rockers are an extremely invasive procedure IF you aren’t starting with a bare media blasted body shell.

All of this is to handle more horsepower, improve the handling, and make the unibody more rigid. My car will have a 347 stroker engine installed which will at least produce 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).

Here's the overall plan:
  • Export Brace: stock OEM Ford type “deep groove” stamping (Scott Drake part)

  • Cowl Reinforcement: weldin the L shaped channel on top side of firewall where the export brace is bolted in at the cowl just like Shelby did on all GT350s (CJPP part)

  • Monte Carlo Bar: straight round tube bar made from thicker walled tube (Street or Track a.k.a. Scott Drake part)

  • Radiator Support Crossmember: this part on my car wasn’t welded to the driver side frame rail (!) and was bent up from a PO jacking on it; replaced with new repro part welded to both sides of frame rail extensions; will also reinforce the RSC c-channel by first welding in a thick walled 2” square tube to each frame rail and flush with the bottom of the frame rails; should make a more rigid tie in across the front frame rails (this is where the strut rod brackets will be welded - to the 2” tube and bottom of frame rails); when complete the OEM RSC part will be welded in over the 2” square tubes; the entire front end will be very rigid, reinforced, and can serve as another jacking point; the extra 2” tube will be undetectable once the RSC is installed over it (RSC = Dynacorn part)

  • Strut Rod Brackets: the strut rod brackets are bent on my car from prior accident and/or being jacked on by PO; will replace with new heavier gauge repro strut rod brackets (Dynacorn parts)

  • Strut Rod Bracket Reinforcement: weld in reinforcement plates at the front of strut rod bracket C channels, effectively boxing in these parts; plates are pressed on a dimple-die for additional torsional rigidity (US Car Tool parts)

  • Extra Welds:
    • seam welds @ top, @ sides, @ front of the strut rod brackets where it touches lower radiator cross member; seam welds @ sway-bar mounting brackets and @ frame rails; plug welds where brackets run under frame rails
    • stitch welds within the front shock towers above where the engine mounts bolt to the chassis as well as full perimeter of the shock towers fender aprons

  • Shock Towers - Outside: outside wheel well area installing lower Trans-Am style stiffening plates (“dog bones”) welded the full perimeter of the "trough" at bottom of shock tower up to just below the UCA mounting points for the Shelby/Arning drop (OpenTracker Racing parts)

  • Shock Towers - Engine Bay side: complete set of plates curving around bottom of shock towers, up over the UCA bolt areas, and connecting shock tower on each side to frame rails (custom fabricated parts)

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

  • Lower Cross Member: heavy duty round tube lower cross member with integrated jackpad bolted in to front subframe (Z-Ray / OpenTracker Racing)

  • Firewall Brace: steel plate bolted in behind brake master cylinder via pedal box mounting bolts with two heim-jointed steel rods connecting to a 2nd plate bolted to driver side shock tower; reinforces firewall as it is an area known to crack and improves pedal feel (Hane Performance part)

  • Roll Bar: 1967 Shelby style roll bar welded @ floor on top of rear torque boxes; additional extensions welded to rear wheel wells; also bolted-in at the top of the roof line (where the 3 point OEM seat belts were boltEd in); technically a 6 point bar but only 4 points are welded; will likely later add a removable diagonal or horizontal cross brace for additional rigidity and allow for installation of a padded head restraint and seat back brace (Mustangs To Fear base roll bar part)

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

  • Convertible Seat Pan: full-width seat pan spans entire width of floor pan; version made for Coupes and Fastbacks without the extra interior Convertible rocker panel reinforcement; stitch welded around the perimeter of pan to floors, inner rockers, and transmission tunnel (Dynacorn part)

  • Rear Seat / Dual Exhaust Pans: additional steel reinforcement plates added to interior of rear floor pans; stitch welded around perimeter of plates intended for mounting dual exhaust but in this case used to strengthen floor and add secure mounting points for rear lap belts (CJPP parts)

  • Sub Frame Connectors: heavy gauge steel c-channels welded in starting at front frame rails...over the existing floor pan supports...welded the entire length of the floor pans back to the rear frame rail...welded around the rear leaf mounting bolt; the c-channel design and full length weld effectively creates a 4 sided boxed-in frame (SpinTech Performance parts)

  • Rear Torque Boxes: additional reinforcement to rear torque boxes with steel pans welded right over rear torque boxes; pans are pressed in a dimple die for increased torsional rigidity (US Car Tool parts)

  • Rear-End: perimeter of gas tank mounting point area to unibody will be reinforced with 1" square steel tubing stitch welded to body; will also added extra stitch welds nearby where frame rails meet the floor pans (custom fabricated)

  • Gas Tank Area: install 11 gauge plate steel cover that sits over fuel tank bolted through with Grade 5 fasteners; combination of reinforced mounting area and steel gas tank cover ties entire rear end together; adds some layer of fuel tank protection if tank crushed in an impact will not compress up into trunk (may later add a fuel cell instead of tank); also adds needed weight to the rear end as 11 gauge cover weighs 25# and will be installing larger 22 gallon 1970 fuel tank (+6 gallons fuel = 30# weight) for extended range (Tank Armor part)

  • Rear Package Tray: Coupes typically also install a metal bead-rolled sheet panel behind the rear seat to add structural rigidity. But this is a Fastback...never seen anyone weld a sheet over the trapdoor opening but I have seen people weld a 1 or 2” tube across the trunk to tie the rear wheel wells together. I’m installing a thick 1/8” aluminum panel that will be bolted into the perimeter of the trap door opening which should provide some rigidity without the weight of a trap door.
Some of the above is probably overkill.

Anything else I should consider?

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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Discussion Starter · #8 ·
No other suggestions?
 

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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.


Sent from my iPhone using Tapatalk
 

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

I’ll 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.
 
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not sure where you get your metal stock from, summit racing has great prices on round & square tubing under bulk stock in the chassis section. 4 ft lengths there is no oversize charge. 8 foot lengths has a $10 oversize charge. still is far cheaper than anywhere online i have found
 

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Discussion Starter · #15 · (Edited)
@bikefreak600 you are reading my mind today - thanks re: Summit! There was no 1” square tubing available at my local Lowe’s and I was looking for another supplier online. Plus when I saw Lowe’s price I was like no way I’m paying that much for it. My old steel supplier back in Atlanta was like 1/4 to 1/3 the price of Lowe’s.

Actually, I’ve already purchased a firewall brace from Hane Performance. Should add that to my above list of structural reinforcement - I forgot I had it! It bolts to the firewall at the master cylinder and then bolts to the driver shock tower.

Hane Performance:
756169


The firewall brace from Hane Performance isn’t cheap, but they’ve been racing Mustangs since 1968, so I figure they know what they are talking about...

Removed all of the glove box, heater, and driver vent assembly today so I could pull the firewall insulation prior to welding. May just delete the heater and defroster at this point. Glad I did remove it as all the firewall seam sealer was dry and crumbling so I cleaned it out. Easier now to also weld up a couple of unused firewall access holes.

Where else and how would you brace the firewall?
 
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Discussion Starter · #16 · (Edited)
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The firewall reinforcement i was referring to goes like this. this is my fastback. it constructed with all 1'' square tubing. One tube on the inside vertical (front) edge of the cowl side. it connects to the torque box & inner rocker. it goes up to the top of the firewall corner. Another tube runs horizontal along the top edge of the cowl side ( underneath the upper cowl flange) starting at the door pillar, it extends forward to the corner of the cowl connecting to the vertical tube. A long curved tube matching the firewall/cowl flange is welded underneath the cowl flange the entire length of the firewall connecting the 2 sides together. it is basically a box "cage" for your cowl & firewall. you can kind of see the tubes in the pics. welding them to the flanges hides them pretty well. The vertical tubes i wrapped the front egde of the cowl side around the tube, it is hard to notice it is there. I also ran forward tubes from the cowl corners connecting the top of the shock towers. this makes the front end rock solid. there is no flexing in this.


 

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When i realized that my shock towers were 1/2'' to narrow at the top because the export brace would not line up. i tried to spread them with that hydraulic cylinder from a engine hoist. it would not spread shock towers apart any more than 1/4'' inch. I had to cut the tubes going to the outer shock tower and re-weld them in place. Now i imagine if i would had tried my hardest im sure the ram could have bent the cage tubing, but that shocked the hell out of me how rigid it made everything.
 

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I would skip the subframe connectors and install ‘vert inner rockers. That’s what I did on my track car. Also stitch the inner plates on the shock towers.

View attachment 755293

View attachment 755295
Would you happen to have any pictures of that? I am doing the same and running into fitment issues regarding the height of the inner rocker, and the shape through the door opening. See this thread >>> Fitting Convertible inner rockers on a coupe....

Thanks!!
 

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Discussion Starter · #20 ·
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