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68 Vert big block structural question

68stang289

68stang289

Member
My 70 Mach is an original 351 car that sometime in the late 70's had the 428 scj swapped into it from a wrecked 70 Mustang. Since it's a non-original 428 car, I don't feel bad about doing my resto-mod or swapping out the 428 before I sell it. My first car 7 or 8 years ago was a 68 Mustang and that has become my favorite body style.

I really want to build a 68 convertible after I graduate law school this year and drop the 428 in there. The motor is built and it's pushing some serious power (front end starts to lift up off the ground when you get on it). I know the verts are less rigid than the coupes and fastbacks so I'm afraid that the power might be too much for the body to handle. Is there anything I could do to stiffen up a vert to help better handle that kind of power and torque? I would assume subframe connectors would help and maybe X-Brace up the under carriage? Would that cause exhaust issues?

I would probably end up selling my Mach after dropping a 351 into it after I finish it to fund this new vert project, but before I even consider doing that I want to make sure I'm not getting myself into a giant headache.
 
As long as you're not going to put sticky tires on the 'vert it should be okay with just SFC's.

Remember that Shelby put the 428 (dual quad) motor in the GT500KR and it didn't really have much in the way of additional structural support beyond what a normal 'vert would have had.
 
Excellent point, I hadn't considered the KR verts. Obviously doing an x-brace or something to that effect on top of the sub frame connectors wouldn't necessarily hurt the car. Anyone here running a built big block in a 7/8 vert?
 
I am in the process of swapping out my 402 rwhp Blown 302 for a blown 331 that should put down 500+ rwhp (I hope). With the 400 hp I have a serious lack of traction and the 331 will be way over the top but that is ok with me. You will need sfc and I am also adding an Y brace that will link the rear subframe connectors to the convertible brace. It is very similiar to the TCP brace but won't require me to modify the exhaust. It will actually connect to the subframe connectors themselves. I plan on bolting it in after it is fully welded. I will post some pictures when I have it done but right now it is just a bunch of steel sitting under the car.

I am starting to notice small cracks that run along the line from the quarter panel to the trunk by the convertible top. I don't know if they are caused by twist or are just happening on their own. I suspect twist. I don't know if this helps but it is what I have run into with my setup.
 
Good deal. 68EFI, I'll probably be contacting you in the future with questions and following your new build up. I'm trying to stay away from a full roll cage if at all possible because I want the more sleeper stock look, with just a monster under the hood. I like the idea of the Y brace to the convertible brace. Those cracks are what I'm looking to avoid if at all possible. Thanks for all the info guys!
 
You could probably build a 4 point cage and hide it with a roll bar similar to the one that 68EFI uses, If you could hide the side bars behind the interior panels and tie them into the frame rails in the trunk.

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Is that crack you are talking about the one that joins the quarters to the panel just in front of the trunk lid? I think Ford used lead in that seam. I saw a video of the Dynacorn Fastback and the builders removed the lead from the roof seam and then mig welded the panels to avoid any possibility of cracking. Maybe this is something you could consider doing? I know your paint is beautiful, but maybe somewhere down the line. I plan on doing this for my 67 vert too.
 
SFC pretty much only help beam action (think of the center of the car sagging). A roll cage is the only thing that will help with torsion.
 
"ZFORCE" said:
Is that crack you are talking about the one that joins the quarters to the panel just in front of the trunk lid? I think Ford used lead in that seam. I saw a video of the Dynacorn Fastback and the builders removed the lead from the roof seam and then mig welded the panels to avoid any possibility of cracking. Maybe this is something you could consider doing? I know your paint is beautiful, but maybe somewhere down the line. I plan on doing this for my 67 vert too.
Click to expand...

I wish I would have done exactly that when I was building the car. I did not and now can't go back and do that without significant expense. I don't think that alone would rectify the problem. I think if you are running a fair amount of power and have a vert additional support is needed.

I have a candy paint job and if I start spot repairs it would be damn near impossible to get the paint to match again. I am stuck with the damage that is already there and will have to make improvements that involve structural support now to avoid the paint issue.
 
Don't believe there's any lead there either but that was an area where Ford used a green colored putty or whatever. Not thick though. A couple things could be done that will not injure exterior paint or interior......WITH CARE. One thought is to replace the gray cardboard trunk divider, the piece that covers up the well liner, with a steel piece that can be attached to the floor and to the drain gutter. Then, where the gutter runs parallel with the 1/4 panel a metal piece 4" wide by distance from gutter lip to wheelhouse top and bolted down as it is too close to 1/4 for welding.
Have replaced a couple drain gutters on 68 cvts as they are prone to rust in damp climates. Handling a good gutter section when out of car, shows how flexible it is. Restraining that area from flex, or twist, should cure the problem. Also, the rear of that section, that houses the top motor could be stiffened where each end attaches to the inner wheelhouse. A steel strap about 4" wide X 4"inches on each end, bent to 90degrees and welded to the inner wheelhouse. This could be done with most work out of sight when lid is opened. Well liner should cover it.
 
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