COP Brief development

When Mr Addis and his team dragged the shell out of hibernation in 1976, they devised a plan to create something special, to compete in and win the hugely popular New Zealand Sports Sedan championship (Conceptual statement). The rules for Sports Sedan racing then allowed virtually any modifications – including fitting any engine of any make up to 6000cc in size, anywhere within the shell – and complete freedom with aerodynamics and suspension. The only real requirement was that the car remained vaguely recognisable!

COP Outcome development and evaluation Mr Addis chose the most popular engine among Sports Sedan competitors, Chevrolet's small-block V8. It was fairly reliable, and could produce impressive horsepower for relatively little cost. He also wanted independent suspension all round, minimum un-sprung weight, and inboard disc brakes. He found what he was looking for in a slightly damaged Lola Formula 5000 single-seater (open wheeler) racing car.

COP Planning for practice

First the team chopped up the Charger body, keeping only the roof, windscreen surround, door sills and pillars, the outer perimeter of the firewall, and the tops of the rear guards. Then a space frame chassis was created on which to bolt the remaining body parts, plus lightweight fibreglass copies of the original body panels. Space framing involves welding metal tubes (in this case seamless steel) into a frame to house all the vehicle's components. If built correctly, a space frame will be significantly stronger and lighter than the vehicle's standard monocoque. It also allows the builder relative freedom when mounting the suspension and engine. And a space frame is far easier to repair in the event of an accident.

COP Outcome development and evaluation
Mr Addis wanted to make his saloon car stop, go, and turn as similarly to a single-seater as possible. To this end the team would utilise as many of the Lola's components as they could.Once the space frame was complete, the Lola's suspension was redesigned to suit the Charger's higher centre of gravity, different roll centres, and greater track width and wheelbase, then fitted into the spaceframe. Addis was very keen to ensure stability through high-speed corners, which required a longer wheelbase. So the team mounted the front suspension much further forward in the space frame than was standard in a Charger.

Another important requirement was to move the weight of the vehicle as close to the centre as possible to provide an even front-to-rear weight bias, to allow the vehicle faster reactions. So the five-litre Chevy V8 was mounted relatively centrally, just beneath the front windscreen.

Finally, a shallow front airdam was fitted beneath the front bumper to help with frontal downforce by pressing the front of the car into the ground at speed. The airdam would also reduce the amount of air allowed beneath the car at high speed, preventing frontal lift, which reduces the driver's control over the car, and therefore cornering speed.

COP Outcome development and evaluation

The team was rewarded for their hard work and creativity with a car that was fantastically fast, particularly in a straight line. It had, however, a tendency to destroy its rear tyres in the course of a race, making life difficult for its pilot. Mr Addis's response was to tear off into a dramatic early lead and hope his rivals would run out of laps before reducing the deficit – not the ideal solution.

The team replaced the five-litre V8 with a six-litre unit. Theoretically, a larger engine requires fewer revs to produce the same horse power as a smaller one, thus incurring less likelihood of wheel spin; and it helped to some extent, once the throttle pedal's travel was lengthened.

More weight was moved to the rear, and the front ride height raised in an attempt to get more weight over the rear tyres under acceleration. A deeper front spoiler replaced the front airdam previously fitted, protruding much further from the front of the car in a gentle slope. It still provided excellent frontal downforce, but allowed the front of the car to move more cleanly through the air. Aluminium side skirts were fitted beneath the doors, also in an attempt to prevent air getting beneath the car, increasing its stability through high-speed corners.

Finally, the team mounted a large rear wing 400mm above the boot lid. This would improve rear downforce, pressing the car into the ground at high speed, and increasing rear grip. The wing was in principle an inverted aeroplane wing. Whereas the latter is designed to keep the plane in the air, the Charger's rear wing was designed to keep the car on the ground; wings of both kinds are more effective the faster the vehicle is travelling.

The wing had to be shaped so that air flowed faster over its underside than its top, pulling and pushing it towards the ground simultaneously. If the design is correct, the air should flow cleanly off the back of the wing, preventing buffeting. The wing also needed to be mounted high enough off the boot lid to avoid the messy air that flowed down the back window and over the lid. With a clean flow of air over and under it, it would press the rear of the vehicle to the ground, improving handling and reducing tyre wear, while slowing the vehicle as little as possible in a straight line.

COP Outcome development and evaluation

The modifications paid off. The team won the New Zealand Sports Sedan championship of 1978. By 1982, the opposition was catching up, and the team decided on more radical modifications to stay ahead. They still had an unused Hewland transaxle from the Lola. The transaxle is a gearbox that bolts directly to the rear of the engine, and runs its own differential to which the rear axles and brakes are mounted, eliminating the need for a drive-shaft. Single-seaters use transaxles so the engine can be mounted directly behind the driver, providing an ideal weight distribution, and allowing the driver to sit extremely low in the vehicle, thanks to the absence of a drive shaft down the centre of the car.

The Addis team utilised the transaxle, fitting the engine behind the driver. A new rear space frame was created to cradle the engine, transaxle, rear suspension, exhausts, and rear brakes. This space frame was bolted to a newly-modified front space frame, and could be detached and rolled out the back of the vehicle in about 20 minutes. A large duct was cut into the roof to force cool air into the engine. The suspension was once again modified to suit the changed weight distribution.

The new modifications proved most effective on the track, except for one rather alarming new tendency. At the very fast Pukekohe circuit, the long back straight has a gentle bend about halfway down its length. It would usually be taken flat out; but the Charger, now with more weight towards the rear, was lifting its nose to the extent it simply wouldn't take the bend. With the extra weight at the back, and with the wing behind the rear axle, a lever effect occurred. Mr Addis found he could compensate for the car's uncooperativeness by wind-ing on full brake bias to the rear, applying the brakes while keeping the throttle wide open through the kink, then winding the bias back before braking for the hairpin corner that followed the straight. Bear in mind, this was all happening at nearly 270kph!

Obviously, a better solution was required. An adjustable front spoiler was fitted, but the answer proved to lie in the rear wing. The team fitted a cockpit-mounted lever that allowed the driver to adjust the angle, and thus the downforce, of the rear wing while the car was in motion – an ingenious solution, and one that would prove extremely effective. So as Mr Addis negotiated the tricky corners, he'd have the wing angled to provide maximum downforce. Then, once on the fast back straight, he'd pull the lever back, flattening out the wing, reducing downforce, and increasing straight-line speed.