an early Mustang can be, and usually is, a difficult task, it is
basically clear-cut. There is typically a great deal of
research involved, especially when restoring something that is a
bit rare or more exotic, but there is (for the most part) really
only one correct answer to any specific question.
On the other
hand, customizing your classic is a totally different project
all together. More and more people are doing it every day.
But, contrary to restoration, building a custom car requires a
completely different set of skill sets altogether.
When you decide
to customize your car, there are many different paths you can
take and many, many decisions you need to make. First and
foremost on the list is the intended purpose of the car. Street
or race (Drag or road). Pro-Touring or Pro-Street. Radical,
conventional, conservative, traditional, retro, futuristic,
far-out, way-out, etc, etc, etc…
And, while all
of these personal automotive expressions can (and do) vary
greatly from one another, they do have one thing in common. The
Your chassis is
the very foundation upon which you will build your project. And
make no mistakes about it; the chassis has a direct impact on
every aspect of your project. And, while there are literally
thousands of products available in the automotive aftermarket,
chassis modifications are few and very far between. This is the
one area that has lagged behind every other aspect of the
hobby. In fact, some have become so dissatisfied with the early
unibody that they have resorted to removing the entire
substructure and dropping the body on a full frame.
to what many may believe, installing a full frame under a
unibody car is not the solution to the problem. In fact it is
taking a step backward. If body on frame construction was the
solution to the problem, you would see current manufacturers
using this technique. And I am hard pressed to name even one.
So come on a
journey with us as we examine the basic chassis structure. We
will show you (in a three step process) how to modify the basic
Mustang chassis. These simple mods will have a significant
impact on every other modification you chose to make.
NOTE: All of
the modifications we describe are based on torsional stiffness
studies performed on the baseline Hopkins NASCAR chassis
designs. It is interesting to note that the major structural
members of the Hopkins NASCAR chassis are very similar to those
of the early Mustang chassis. All these modifications can be
made on any Mustang (stock or modified) without having to
repaint the exterior of your car.
goal is to drive (or transmit) as many of the torsional forces
seen by the chassis up into the roof structure. In order to
transmit these loads effectively, we must start with the base.
Adding rocker Reinforcements, installing torque boxes and
replacing the individual driver and passenger seat pans with a
seat pan that extends all the way from one rocker to the other
(bridging the trans tunnel) are the bare minimum modification.
Fortunately for us Mustang owners, these parts were designed by
Ford and are standard components in all early convertibles.
Installing these items requires a minimum of modification.
Anyone capable of replacing a quarter panel is capable of
installing these items.
modifications will reinforce three key areas of your chassis.
First, reinforcing the rockers will net big results in regard to
torsional stiffness of the chassis (Note: You will also see big
gains in regard to “beam” strength. Rocker reinforcement
improves beam strength more so than the addition of sub-frame
connectors. You will note that we are not recommending
sub-frame connectors as part of our chassis package.). The
rockers are rated as the sixth most sensitive structural member
in regard to torsional deflection. Second, adding torque boxes
will tie the frame rails to the rockers, again, netting big
results. The torque boxes (or equivalent NASCAR structures) are
rated as the fourth most sensitive structural member in regard
to torsional deflection. Lastly adding the convertible seat pan
reinforces the rockers by tying them together and also
reinforces the trans tunnel. These three simple modifications
will drastically improve the base chassis.
In fact, these
are the very modifications the Ford engineers implemented in
their black 65 fastback “Cammer” project car.
In our project,
we had some minor floor damage. We could have repaired the
rotted out areas of the floor by installing patch panels, but we
opted for a full floor replacement. Ultimately this netted us a
much cleaner and simpler installation. If you have rusted
floors, I would recommend this procedure in a heartbeat.
Above is a
view of the chassis with the floor removed. Note that we also
had to remove a section of the firewall. This area will be
repaired after the installation of the torque boxes.
photos show the inner rockers prepped and ready for the addition
of the convertible rocker reinforcements.
Above, we are
installing the convertible inner rockers. There are very stout
items and add a great amount of stability to the overall
Above we see
the installed inner rocker reinforcements.
Above you see
the installed firewall patch panel. You will note that the
patch panel is installed via a spot welded lap seam. This
technique is stronger than a butt seam. The finished seam is
typically covered with seam sealer, but the seam can also be
welded and ground to achieve a seamless installation.
Above we see
the installation of the convertible seat pan
Above is a
bottom view of the drivers side torque box
You will note
that we moved the seat pans back 3” to give those taller drivers
a bit more leg room. Also we seam welded all of the torque
boxes and suspension mounting points.
Now that we
have made the “base” stable, it is time to address the forces
applied to the chassis by the front suspension. In the case of
the early Mustang, all front suspension loads are carried by the
shock towers (and to a lesser extent the front frame rails).
These loads are carried to the roof structure through the sheet
metal of the engine compartment aprons and the cowl. To
reinforce these areas we must box the cowl area with structural
tube and then triangulate that structure to the “A” pillars and
the top of the shock tower.
modifications will reinforce two key areas of your chassis.
First, tying the shock tower to the cowl will greatly stabilize
the front suspension. This area is rated as number two on the
list of most sensitive structural member in regard to torsional
deflection. Second, reinforcing the cowl will carry the forces
applied by the front suspension directly to the roof structure
(as well as the rockers), again, netting big results. The cowl
structure is rated as the ninth most sensitive structural member
in regard to torsional deflection. Now, when you add that
expensive aftermarket front suspension, it will perform exactly
the way it should greatly improving road feel, grip and
phase one and two (in addition to the installation of an export
brace and Monte Carlo bar) will reduce over 87% of the
deflections seen in an un-modified chassis.
Above is a
good view of the cowl reinforcements. This entire structure is
designed to transmit all the front end loads through the cowl to
the rockers and the “A” pillars.
installation of the structural tubes, trim panels are
installed. These panels not only keep debris from accumulating
in all the nooks and crannies, but also sandwich the structural
tubes between two sheet metal panels helping to stabilize the
Here are some
views of the final trim panel installation. These trim
panels are installed to keep these areas clean and help prevent
the accumulation of road debris in the structure.
Here is the
Here is an
example of just one of the welds holding the front structure
Phase one and two is all that is typically required for a high
performance street driven vehicle. But for those of you who are
looking at installing engines rated at over 600 RWHP, we
recommend installing a full cage. The cage will not only
increase overall chassis stability, but also help protect the
passengers in the event of a crash or rollover.
a cage that will strengthen the chassis and reduce torsional
deflection is a bit different than installing your typical run
of the mill roll cage. Most roll cages are designed with one
purpose in mind; satisfy the safety regulations of a race
sanctioning body. They are designed to protect the occupants in
the event of a crash or rollover.
designed cage will reinforce as well as help transmit loads to
and from key structural elements. In our case, the roof
structure just above the drivers and passengers side windows,
the “A” pillars and the roof structure at the top of the
differences between our design and the typical roll cage are as
follows. The cross bracing of the main hoop. The triangulated
3 bar rear frame rail braces. And the additional bar braces at
the four halo connection points. In addition to these
differences, the “A” pillars, and the roof “halo” are gusseted
to the existing Mustang structure. Tying the cage to the
existing unibody structure is extremely important if reducing
torsional deflection is your goal. If the two structures are
allowed to float independently, minimal gains, if any, will be
seen in regard to overall chassis stability.
modifications will reinforce three key areas of your chassis.
First, tying the cage to the roof structure over the drivers and
passengers side windows will generate the single greatest return
in overall chassis stability. This area is rated as number one
(by a large margin) on the list of most sensitive structural
member in regard to torsional deflection.
reinforcing the cowl will carry the forces applied by the front
suspension directly to the roof structure (as well as the
rockers), again, netting big results. The cowl structure is
rated as the ninth most sensitive structural member in regard to