Ever since I saw Lance Corsi's halo roll cage, I had imagined that I would do something similar for my coupe but I always heard that nagging voice from owners of roll cage-equipped street cars in my head about the need to wear a helmet all the time to keep your noggin from being bashed in on bumpy roads or from aggressive driving. Last week I finally removed the hard top from my body fitting stage, placed it upside down on saw horses and took a serious look at other options.
For my decision, I tried to be realistic about conceivable scenarios versus the ultimate no-no which is getting upside down (or worse: upside down then right side up, sideways, repeatedly!!). Any coupe owner at this point will have stuck a flashlight up the A-pillar and said to themselves "holy s*#t, that piece of metal ends right there, not a third of the way up the pillar"!! Not the greatest thing if, like Lance postulated, you took out a deer at the knees. I then looked at the structure of the pillar's cross section, how it blended into the ducting of the engine's upper air intake tract and roof and an idea began to form: why not use some of that pre-formed 3-D hoop to help with strengthening the structure. Tossing the idea around with my race-car fabricator neighbor, we both liked the idea of filling that void with something substantial, impact absorbing and fairly light weight. A quick trip to the internet yielded pay dirt: 16lb 2-part expanding urethane foam. Trust me, this is not the same as "Great Stuff" from the hardware store. I got some today from USComposites, mixed up a sample, and HOLY CRAP that is exactly what I was looking for! You would need a hammer to even make an imprint on this stuff. Further research revealed that high-performance boat manufacturers have switched from sandwiched, marine-grade plywood transoms to this stuff with excellent results. Better yet, in an enclosed structure like the A-pillar, it bonds the outer fiberglass skin to the inner ducting to make one really rigid structure that I believe would seriously increase the safety structure of the car, probably even in the event of a roll over. My calculations show it should add a net weight of 6-8 lbs to the finished car. Not too bad!!
Before I get too over-zealous, let me be clear I have NOT yet integrated this product into the car. I also acknowledge that there is no realistic way to substantially increase the structure across the top of the windshield besides a roll bar...but oh well, better something than nothing. Christmas duties prevail till after the holidays but let me share what I have done so far.
First, I cut a slot into the ducting where the A-pillar duct meets the upper air inlet tract, made a cardboard template of it's cross section, then transferred that to a piece of fiberglass, cut it to fit and glassed it into the slot. This will keep the foam from expanding into the air inlet tract. Also, there is a quasi-bulkhead in the A-pillar at the upper windshield area that Factory Five placed to probably block off air flow downwards out the bottom of the pillar. This will necessitate placing the expanding foam from different points in successive pours, but that is an easy aside. I will document the process in it's entirety next week.
I had also entertained the idea of filling the B-pillar with this product, but after careful analysis, have concluded this to be a futile effort: The B-pillar's structure has to be terminated by an (already existing) bulkhead where it intersects the upper air inlet tract, so any crash loads can't be transferred to the upper roof structure. This is also mitigated by the car's main roll hoop being only 5 inches behind this area. The law of diminishing returns prevails here.