Facing up to a stiff challenge

How do you turn a family-friendly Astra coupe into a championship-winning demon of the track? Jon Excell visited Triple Eight Race Engineering to find out.

For legions of motorsport fans, it doesn’t get much more exciting than F1 – the speed, the glamour and the superstar drivers make a compelling blend. But, for a growing number of enthusiasts, F1 is simply too remote: the drivers lead lavish pop-star lifestyles, and the cars, although impressive, don’t really relate to the average driving experience.

Enter the British Touring Car Championships (BTCC), an aggressive high-octane contact sport where the cars look like the sort of thing you could buy from any high street dealer, and the drivers are affable and approachable.

With this year’s season over, Vauxhall’s VX racing team has just been crowned 2003 British Touring Car Champion, taking the manufacturers’, team, and drivers’ titles for the third successive year. John Morton, chief designer at Triple Eight Race Engineering, the company charged with turning an Astra coupé into a race-car, explained the engineering challenges.

The design of touring cars is heavily constrained by regulations intended to reduce cost; the design and development of a two-car team now costs around £1.5m compared with the pre-regulation cost of around £6-10m. These rules affect the amount of modification possible on almost every area of the car.

Despite this, as three consecutive years of victories testify, Morton and his team are adept at using whatever design freedom they have to beat the competition.

So how does the performance of the race-car compare to its highway-bound antecedent?

It’s perhaps misleading to compare the two in terms of speed. For instance, while the road-car might have a more impressive 0-60mph, the lowest gear on the race-car will take it past 100kph (62mph) in about five seconds.

The top speed that the VX team cars race at is around 250kph (155mph), although the potential speed is actually higher. This is because even Thruxton, the UK’s quickest circuit, has a number of slow sections, and on the rest of the circuits the maximum length of straight is just 548m (600 yards).

Morton prefers to compare the vehicles in terms of power, and while regulations insist the 2.2 litre engine is reduced to 2 litres, the power of the car is doubled, up to about 280bhp.

At 1,030kg the race-car is also considerably lighter than its 1,205kg road counterpart, and is capable of tolerating cornering and braking forces up to 2G – around double that of a road-car.

The transformation begins with an unmodified Astra coupé base shell, which is made 10-20kg lighter by burning off the waterproof underseal and removing every unnecessary bracket.

Then, using information from the base shell, a roll cage is designed and, before it’s made and dropped in the car, finite element analysis (FEA)software is used to simulate its behaviour within the shell.

While safety is the cage’s primary function, it also serves to stiffen up the car. ‘An important figure for a race-car is the torsional stiffness between the front and rear suspension,’ said Morton.

A road-car has a flexible body which means the whole vehicle behaves like a great big undamped torsional spring, limiting driver control. Morton estimates that the introduction of the roll-cage effectively quadruples torsional stiffness. With the cage in place, bushes and brackets for the pedal box, and engine mounts are all jigged in position.

It’s at this point that the regulations really begin to kick in, with the team obliged to keep the road-car’s steering rack and some of the original suspension components.

While the steering rack is not particularly problematic (road-car racks are pretty robust) the suspension system presents Morton’s team with a more significant challenge.

He explained that a road-car’s suspension is designed to provide a comfortable, vibration-free ride, and its true performance is compromised by, for example, rubber bushes in the wishbones and dampers. So all rubber bushes are replaced with rigid spherical joints of hardened steel with PTFE liner.

The front and rear sub-frames are the main elements of the suspension that must be carried over from the road-car, and in the unending quest for precision, high loads and control these are mounted stiffly on the car.

Considerably more design freedom is granted on the other suspension components, and Morton’s main concern is making these as light and stiff as possible.

‘Everything we do is as light as possible, which means we have to use analysis software on almost everything to get it as light as possible and still take the load and keep the optimum stiffness – all done before it reaches the car,’ explained Morton.

The engine, based on a 2.2 litre Astra coupé unit, is perhaps subject to the most specific regulations. Only normally aspirated engines are allowed and the maximum rpm is electronically limited to 8,500. Valve diameters have to be the same as the road-car engine with a maximum allowed lift of 12mm. No variable valve timing is allowed.

The block, cylinder head and sump have to be original, although material can be removed by machining and grinding.

Despite this, French company Sodemo has done a good job of modifying the engine as much as possible, designing the internal components from scratch in order to increase the breathing and combustion efficiency and reduce overall friction. A race-type inlet and exhaust system have been designed to get the best out of the new hi-tech internals. Both the oil lubrication and water cooling systems are revised to suit the now higher requirements of the race engine.

The engine is also easy to drop out of the car. Mounted using two bolts either side of the engine and six bolts on the subframe, it takes about an hour to drop out and install a unit – about a week’s work with a road-car.

The transmission, a TOCA standard part, is a six-speed sequential gearbox manufactured by Xtrac. This is mated to the Vauxhall engine through the AP racing multi-plate clutch and a bell housing designed by Triple Eight.

Another restriction imposed by the regulations is the car’s aerodynamic design. It must still look like an Astra, so Triple Eight is restricted to what it can do. The aerodynamic tuning of a touring car is, said Morton, all about minimising drag, providing downforce and balancing this downforce between the front and rear. This creates a trade- off between downforce and drag – which is largely dealt with by subjecting scale models of cars to numerous wind tunnel tests.

The amount by which the race-car is modified tells you that the original Astra coup̩ is not designed to race Рand that, said Morton, is where the fun and the challenge lies.

It is perhaps in the driver’s environment that the true extent of the modification process is most keenly felt. The interior is unrecognisable as a family Astra except for the orginal dashboard – although hollowed out – because the in-car camera must be looking over the driver’s shoulder at something that looks like an Astra. Morton admits that although every part of the car has been changed or modified so it’s nothing like a road car, the team is aiming for the illusion that it is operating something that came out of the factory – with a bit of a tweak.