Bodywork - "Don't fall to pieces now..."

This section outlines the structural modifications necessary to keep a 1600 racing when all it wants to do is fall to pieces. This includes bracing, seam welding and weak points.

Roll-Cages

A 1600 shell is definitely not the strongest monocoque around. For starters it only has a half chassis (i.e.. the front chassis rails end just behind the front seats). After several races you'll find that the spot welds in various places around the car start pulling apart. There are only three things you can do to alleviate this problem:

Seam weld the existing panels.
Brace the existing panels.
Get another car.

The requirements of offroading dictate that a roll-cage must be fitted to the car. This can serve the dual purpose of both protecting the occupants during a crash and bracing the body shell of the car.

Different classes of racing will require various roll-cage designs (see your handbook), however we settled on a braced main hoop with additional bracing both forward (along the roof-line) to the front foot wells and back (along the roof-line) to the parcel shelf. An additional brace is run directly under the dash. The regulations are changed regularly so it will be necessary to read the handbook carefully and not just look at other cars.

There's a couple of different ways you can go with the standard roll-cage. The first is a bolt together job. It has the advantage of being relatively easy to install. The second method welds all members together. This provides a stronger roll-cage and is usually a tighter fit with the existing shell of the car, however it generally costs more.

Obviously the size of the tubing is governed by the regulations. They dictate specific wall thicknesses and inside diameters for various alloys/metals. The scrutineers will not have a problem with an over-engineered roll-cage, however it will cost you in terms of weight. This is one of those trade-off situations. Do you want to feel safe sliding down a gravel track at 160kph or is the bare minimum enough?

When you design your roll-cage you must take into account the positioning of certain items in the car. A short list follows:

Existing chassis members (you want to pick these up if you can)
Driver, co-driver seating arrangement (allowance for head movement and space for driver's feet/pedals)
Seat-belt mounts and angles (the shoulder straps should be as short as possible and angle down between 10 and 45 degrees)
Additional bracing for front/rear suspension towers and/or other suspension points (particularly shock/spring locations)
Dash

We chose the bolt-together type, because for some reason we thought it necessary that the roll-cage was removable. In hindsight (all motor racing should be conducted in hindsight!) it would have been far better to weld the cage in. This would have given us valuable extra room inside the shell, needed especially in the head area (1600s not being the largest cars on the market today).

We made provision in our cage design for later addition of bracing from the front strut towers back to the firewall, side intrusion bars between the main hoop uprights and front uprights, as well as the possibility of adding some smaller members to pick up the floor of the boot (from the parcel shell). As anyone who has ever had a 1600 will tell you, they have a nasty habit of splitting just behind the back doors (in front of the boot). The result of this is the entire boot sitting on the ground. If you plan on putting anything heavy on the floor of the boot then bracing will have to be done.

Seam Welding

This is the process where-by existing panels that are connected only by factory spot-welds are re-welded to provide additional strength. It is not necessary to weld the entire join between two panels, a 50% coverage in 50mm beads will suffice. A MIG is especially useful here (compared to an arc welder they're especially useful everywhere!) as the panels are rather thin and it's quite easy to blow holes in them (oops!).

Areas of the car that need special attention are the entire front end (strut towers, cross members, firewall, etc.) and the rear shock towers. The front end is especially prone to breaking/bending/shearing and needs all the support you can give it.

Another area prone to breaking are the radius arm rod mounts. You may not realise this until one of them breaks off and leaves you stranded in the middle of nowhere; but they need more than a couple of spot welds.

Bracing

The majority of bracing should be performed at the front end of the car. It is a sad fact that 1600's front ends are just not designed to handle the rigours of offroad racing.

It will be necessary to strengthen both chassis rails (as they are prone to buckling) and reweld/replace the existing front cross-member. We have also added gussets and additional bracing to the front cross-member (for strength and to pick up the engine mounting points).

We also added a couple of braces from the tops of the strut towers down to the front cross-member. This will hopefully stop the strut towers from receding too far towards the firewall. Unfortunately, the effect of this triangulation in front of the tower places additional stresses on the chassis rails just behind the existing cross-member. The result is severe buckling, so it might be an idea to weld in some additional support in these areas.

You should also think seriously about bracing the tops of the strut towers back to the firewall. This would stop the area between the firewall and towers flexing and hopefully prolong the life of the body shell.

Sad to say, but if you want a strong body, then get a 1 tonne Holden ute. Unfortunately driving one of those is like driving a tank (I should know, ~~I've got~~ I had a HQ Monaro). Everything's a trade-off: weight, power, strength, etc, etc, etc.

You'll also need some bracing on the tops of the rear swing arms, covering the axle bearing carriers. These carriers tend to break off the swing arms and you lose the carrier, axle, brakes and wheel. If you're lucky you'll have a sway-bar mounted to the swing arm so the spring and shock won't disappear. This doesn't matter because 2 seconds later (if you're running the standard single circuit brake master cylinder) you'll realise you have no brakes as both the hydraulic line and the hand-brake line have been torn off (see the brakes section).

Lastly, the rear cross-member has a weak point directly below the passage for the exhaust. What tends to happen is that the metal cracks through the thinnest region and splits upwards. We found that welding a section of flat bar under the diff works a treat. It's strengthened the entire area and doesn't weigh it down too much.

Note that even though you should use a strut-tower brace, the one pictured on the left is not really good enough. The brace should preferably be as straight as possible between the tops of the towers and there should be additional top support to stop the tower from being crushed sideways.

This brace was actually a result of needing a mounting point for the oil cooler (it was mounted to the front-most bar, however it has since been moved). As yet we haven't replaced the brace as the new design will be integral with the proposed cold air box.

Note the brace that extends from the top of the strut tower to the front chassis member. Them there's good triangulation.

Unfortunately, the larger fuel tank (see the fuel section) has prohibited the installation of a rear strut-tower brace. It looks as though the fuel tank will have to do a couple of things where it is...