Trimming the main hoop height is best done in a series of small cuts to avoid going too far. A chop saw is best though you can get by with a hack saw if you’re careful and make clean, even cuts.
On unit-construction cars (that means virtually every popular Mopar) the NHRA mandates that each tube and strut must be welded to a 6x6-inch, 0.125 minimum thickness steel plate that’s welded to the floor pan (it is also permissible to bolt these plates to the floor with a minimum of four 3/8-inch bolts as long as a second plate is also present beneath to “sandwich” the floor pan). The Competition Engineering kit comes complete with six mounting plates. Keep in mind, while these plates can be formed to fit the underlying floor surface, they cannot be trimmed in a fashion that reduces their original 6x6-inch size. Here Dale taps the main hoop mounting plate to center it prior to welding. On full-frame cars (many GM and Ford models) the rulebook states; “All cars with an OEM frame must have roll bar attached to frame”. That means Brand X guys have the added burden of blasting holes in the floor pan to get to the frame rails. Bummer.
he NHRA rule book also states that the rear struts must be welded to the main hoop at an angle that is at least 30-degrees from vertical. While it is legal to mount them as far as 5-inches down from the top of the main hoop, the most practical approach is to mount them to the horizontal span of the hoop as shown here. Using a magnetic protractor, Dale establishes a legal-eagle 50-degree angle that places the feet of the struts conveniently against a section of floor that’s backed by the Dart’s sub frame which ties the car together nicely.
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| All paint, body seam sealer and surface rust scale must be ground away prior to welding of the mounting plates. | To get the plates to conform to the Dart’s irregular floor pan surfaces, Dale welds a small section in place then hammers it down flat with the floor. He then welds the gaps before using the hammer again to form the next section. This method is a foolproof alternative to attempts at forming the plates on the work bench with a hammer and vise. | A final distance measurement is taken before the rear struts are cut for the final time. We need them to be 40.5-inches but Dale leaves an extra inch to accommodate the 50-degree cut he’ll put at the foot so it merges with the mounting plates without creating gaps. |
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| Creeping up on the orientation of the foot allows a clean merge with the mounting plate. The small pile of remnants is made one by one as the ideal shape is sought. After each cut, the strut is test fitted and marked where further trimming is needed. | Once the strut is trimmed to it’s ideal configuration, it is tested on the opposite side of the hoop. Thanks to Dale’s continuous effort to maintain symmetry, the strut is an exact fit on either side of the hoop. Rather than go through the hand fitting process all over again, he simply transfers the cut line onto the other strut and in one chop, it’s ready for installation on the opposite end of the hoop. | The door struts must be mounted so they intersect the occupant’s elbow and shoulder as shown to be NHRA compliant. |