We got the inside track from Toyota Gazoo Racing South Africa’s team principal on what makes the Hilux racer special...
Three hours. Provided there’s no damage to the bakkie, that’s how long the team works on the Toyota Gazoo Racing South Africa (TGRSA) Hilux when it stops in the bivouac after a Dakar Rally stage. As I enter the temporary service area of TGRSA outside Pisco, Peru, the technicians swarm round the three Hilux racers; they’re removing and checking key components before refitting and tightening the bolts to the correct torque setting. It is a meticulous process running like clockwork under the watchful eye of team principal, Glyn Hall. To win Dakar requires luck and driver’s skill, but it also calls for a machine capable of facing everything the desert can throw at it while travelling at breakneck speed. This is what it takes to be a Dakar Rally champion.
Every sport is governed by regulations and the Dakar is no exception. The top class in the car section is the T1 and it’s based on the set of regulations stipulated by the FIA for cross-country rallies. These regulations are slightly adapted for Dakar because another French establishment runs the event: Amaury Sport Organisation (ASO).
The TGRSA Hilux falls in the T1.1 category for four-wheel-drive vehicles powered by a naturally aspirated petrol engine. Although the rules are comprehensive, the defining constraints are minimum mass of the vehicle depending on engine capacity (Hilux: 1 850 kg); the air-inlet restrictor size for the engine to limit power; and the fact that 4x4 vehicles have to use smaller-diameter wheels and aren’t allowed to alter tyre pressures on the move.
The Hilux employs a Lexus 5,0-litre V8 tuned to make the most of the available air through the 37 mm air restrictor. Therefore, the aim was to maximise mid-range torque, with 600 N.m available between 4 000 and 4 500 r/min. This is possible by utilising the variable valve timing (60 degrees on the intake and 30 degrees on the exhaust valves), as well as the pressure-wave dynamics in the airbox and exhaust system, to achieve a volumetric efficiency of 120% (20% more air than the theoretical cylinder volume at atmospheric conditions) in the mid-engine speed range. The powerplant is mid-mounted (underneath the crew) to allow for a 50:50 mass distribution. As the engine is moved so far back, it is not visible under the bonnet. To get the drive to the front axle was a big challenge, according to Hall.
Aviation fuel (avgas) is used because it’s rated at 102 octane and the quality can be guaranteed in Peru. Injection is controlled by the engine control unit (ECU) through port and direct injectors, resulting in 16 injectors in total. The ECU can switch between port and direct injection for performance, depending on load and speed, and can even flip to a single strategy if there is a problem with an injector. Lambda (the air-fuel ratio) is kept between 0,88 and 0,92 for maximum power.
The bladder-type fuel tank holds 540 litres and is FIA-regulated for safety. The 0,72 kg/L density of avgas means the fuel load can add up to 389 kg when the tank is fully fuelled. The location is close to the centre of gravity (COG) of the vehicle to limit the effect on mass distribution and proprietary dividers, and sponges are used in the tank to avoid fuel sloshing around.
A six-speed Sadev sequential transmission (with flat-shifting capability) sends drive to all four wheels. The mechanical limited-slip differential on each axle is tuned to deliver the correct ramp-up and -down rates. Most drivers prefer the differentials to lock gradually under acceleration but open quickly during braking to help the BF Goodrich tyres find traction. The 320 mm brake discs and callipers are produced by local supplier Powerbrake and the callipers are watercooled to remove excess heat under hard deceleration.
According to Hall, half of the development time is spent on the suspension setup. This is crucial for an off-road racer and has the biggest influence on maintaining race pace over rough sections. TGRSA employs two coil-over Reiger dampers at each corner of the Hilux (which features fully independent suspension all-round). The reasons for two shocks are both performance and a form of dual redundancy if one should break. The regulations allow just 280 mm of travel and most of this is used with hydraulic end-stops to avoid metal bump stops.
The interior resembles that of a light aircraft, with numerous screens and switches controlling the vehicle and GPS. The navigator is largely responsible for operating the systems and investigates faults detected by the onboard diagnostics. The ECU monitors more than 1 000 signals to determine the status of all the components. For example, even differential and shock-absorber temperatures are monitored.
The vehicles don’t sport many convenience features but do have air-con, although it cuts out when full power is required, which is quite often! Each day, drivers are allocated three litres of fresh water and energy drinks for the race. Because of the noise, headsets are used for communication.
Any racecar is only as good as the team supporting it. For Dakar 2019, more than 30 people played their part. They set up the service area in the bivouac, serviced and fixed vehicles throughout the night and were ready to repeat it all again the next day. Sleep was a luxury. Spares were carried in three support trucks with enough components to build another three Hilux racers. The fact that all the vehicles were locally made at the Hallspeed facility in Midrand is truly a proudly South African achievement.
There’s a reason the Dakar is said to be the toughest motorsport event in the world. Breakdowns are common and can vary in severity, from a puncture or a snapped driveshaft right up to complete powertrain or suspension failure. Not all problems can be repaired on a stage but the vehicles nevertheless carry an emergency repair kit which the driver and navigator (now technicians) can use to try and get the Hilux mobile again.
The kit’s content varies for each stage (with mass ranging from 50 to 100 kg) but core additions include a driveshaft, suspension wishbone, steering control arm, steering joint, plus a toolkit weighing 7 kg including a battery-powered impact wrench.
Integral hydraulic jacks (powered by the power-steering pump) lift a side of the Hilux off the sand. Race crews practise general repairs and Nasser Al-Attiyah’s average time for wheel changes is 83 seconds. Impressive considering it includes getting out of the race harness before changing the wheel, jumping back in and firing up the engine.
By limiting airflow to an engine, power is curbed. That’s the function of the 37 mm restrictor in the air intake of the Hilux. We asked Dr René Heise, aerodynamicist and ballistician, to calculate the maximum theoretical airflow through the restrictor using compressible flow calculations at standard atmospheric conditions (Dakar 2019 was run mostly close to sea level). This is then compared with the theoretical airflow through the engine if it is seen as an air pump displacing five litres of air every second revolution (100% volumetric efficiency). The graph below shows the engine is air (and power) limited after about 5 300 r/min. Therefore, there is little point in revving much higher, as there’s little performance gain.
Original article from Car