I was looking for a local shop to form some panels and discovered Back Bay Customs which is about 60 miles north of Boston in Portsmouth NH. After seeing one of their cars in Boston, I spoke with Adam, the owner, and decided to haul my car to the shop. I’m very picky about my car and I was pleased to see a large tidy shop, lots of metal forming equipment, CNC plasma table, paint booth, and multiple fabricators. I’ve been very pleased with their creativity, fabrication skills and communication.
The first project was the upper firewall. Sealing this area for heat, sound and vapors is critical and the stock firewall left a fair number of gaps, so we decided to replace it. Adam noticed that the firewall wouldn’t sit flat on the traverse 2” x 6” chassis tube. WTF?
The issue was that the two mounting brackets for the rear hoop legs weren’t coplanar with the 2” x 6.” One was 1/8” forward and the other was in excess of 3/8” forward which resulted in the top of the firewall tilting towards the cockpit while also imparting a left-to-right twist. This looked like ass and made it impossible to get a good seal. The solution was to cut off the brackets, grind the hoop smooth, fabricate two different brackets to account for the variance in offsets and weld everything.
Replacement brackets welded in place. Notice that the left bracket projects further than the right bracket
The next step was to fabricate a blister to accommodate the induction tube which projects into the firewall. To fabricate the curved corners, Adam made a paper pattern, cut and annealed 1/8” 5052 sheet, and then used a soft mallet and a slapper to stretch it over a post dolly. During the shaping process he had to anneal the sheet several more times to keep it soft. He then trimmed the shaped piece to match the pattern, tweaked the middle section and welded it together.
From left to right; soft mallet, slapper, profile gauge, and post dolly
Blister mocked in place
Once all of that was done the firewall still had too much flex which was remedied by welding tabs to rear hoop’s upper radii. This is particularly important because most SL-Cs, including mine, mount a large coolant expansion tank to the upper firewall.
Firewall support tab tacked to the rear hoop
The cage is nicely fabricated and serves its primary structural/safety purpose well. However, it falls short in multiple areas which result in either unnecessary compromises or a lot of work for the builder:
The front hoop doesn’t fit the body well which impairs vision and results in massive A-pillars. I fixed that issue in this post. Given the large number of SL-Cs that have been produced, RCR should have started CNC forming the front hoop long ago.
Perhaps it’s just my car, but there’s no excuse for the issues with the rear hoop leg brackets. It was downright sloppy. There should be a jig to ensure alignment and a quality check before the car ships.
The small tabs in the upper corners should be stock. While this is a trivial fix, not all builders have easy access to welding equipment and it’s a shame to wreck the nice power coat finish that comes from the factory.