Part 2 - All Barred Up
With all the panel work done on our new Mazda 323 GTX, it was time for the installation of a full Group A-spec roll cage.
We decided to go the whole hog with a fully welded-in chrome moly roll cage, and chose Brown Davis Automotive in the Melbourne suburb of Bayswater to perform the job.
Well respected in the sport for their installation of roll cages, Brown Davis boss David Brown was more than happy to jump aboard the Mazda project and offer his company's service and expertise. Brown has an engineering background, having done the course at university and his business is one of the oldest CAMS licenced manufacturers for aluminium roll cages (no licence is required for steel or Chrome Moly cages, but one is required for aluminium).
Chrome Moly was the material chosen for the cage, as it would offer the best possible strength, as well as being very light. Chrome Moly is also smaller in diameter than steel and was able to be welded to the body, unlike aluminium.
Aluminium has a similar strength to weight as Chrome Moly, however it is bulkier and physically bigger for the same strength, taking up more room inside the cabin of the car.
As the car was being built to Group N specifications, the homologated roll cage had to be used, another factor in choosing Chrome Moly. If you are building a car to PRC specs you can use any type or style of roll cage you wish, but to run a car in Group A or Group N you must use the homologated roll cage design.
The design of the cage was taken directly from the Mazda 323 GTX homolgation papers and had all the normal features of any roll cage, including side intrusion bars, as well as bars going through the firewall to the strut towers.
The interior of the car had to be completely stripped out before installation of the cage could be started. That included the removal of all trim and carpeting, as well as the dashboard and, where possible, the windows. If the windows are left in, welding splatter can bum the glass, making them unuseable.
After the initial hoop made of 45mm diametre Chrome Moly was bent into shape and welded into the car, the difficult job of fitting the rest of the bars in place started.
David Brown, after finishing the cage, admits that it was the hardest roll cage his firm has ever had to install, but the finished job is superb and is a real work of art.
One of the difficulties in the fitting of the cage was keeping the bars in line with the shape of the cabin of the car, and in the case of the bars coming down from the top of the windscreen to the floor, meant putting five bends in each side.
Five seperate skins were also needed to be cut through for the bars going to the strut tops, but after much swearing and cursing, it was achieved with first class results.
Apart from the main hoop, the cage is constructed of 38mm tubing and is Tig welded. However, the plates which connect the roll cage to the floor and the front and rear strut towers are Mig and stitch welded, so as not to heat or weaken the bodyshell more than is absolutely necessary.
The cage Brown Davis Automotive constructed in our Mazda 323 GTX would cost the average competitor between $4000 and $5000, far more than the $1000 special you may be able to install yourself with mild steel, a pipe bender and a good welder. However, with weight an all important factor in special stage rallying, particularly in the Group N category, the extra money spent can prove beneficial on the stages.
And, more importantly, you know you have a professionally built roll cage that will give you and your co-driver the best possible protection in the event of a serious accident.
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