How To Build A Rally Car
Ever wondered what it takes to turn a car taken off the production line into a competition car capable of challenging for the British Rally Championship? It's a huge task. Here the latest Evolution 2 version of the SEAT Cupra Sport Ibiza which Gwndaf Evans will drive this season goes from a bare shell and roll cage to the complete car ready for testing and the rally in Wales.
SEAT Ibizas are tough cars but look at the punishment Gwyndaf Evans or Harri Rovanpera gives his over hundreds of miles of rally stages and you wonder it survives, let alone wins. Watch one being up before the season and you start to understand. This particular car came off the SEAT production line near Barcelona like any other then the rallymen descend on it, preparing it for Harri Rovanpera's use in the 1997 F2 Rally Championship. The make over is incredibly thorough with the completely stripped shell fitted with a full roll cage. Yards of thick 48mm tensile chrome-moly steel completely surround driver and co-driver.
It serves two purposes, obviously to providing a survival cell that can withstand rolling the car off the side of a mountain, with impact bars strong enough to take high-speed slides into unyielding trees and rocks. Crew safety is just part of the story though; the cage connects all the crucial points of the car together, which in a race or rally car is basically all the suspension pick up points, and it keeps the shell in alignment whatever punishment it suffers.
Welding in a roll cage alone makes the car far stronger than the standard road car but rally cars need to go one stage further. The various panels that go to make a road car are just spot-welded together with small welds every two or three inches. Look at every panel join on this Ibiza and there's a continuous line of weld along each one. This seam welding, along with the roll cage produces a structure with a torsional stiffness of 26,500 lb/degree. That's several times stiffer than the normal road car, far more than the old Evo 1, and nearly as stiff as a BTCC Touring Car. This strength and stiffness is absolutely vital because rally cars have to survive as precision racing machines.
That precision starts in the factory in Spain where new suspension mounts to take the specialised components used are welded in with extraordinary accuracy on jigs. The aim is to have each point located exactly where the design engineer's computer has dictated, to within a quarter of a millimetre. Contrast that with a road car. Once the effect of looser production tolerances, coupled with the use of rubber mounting bushes, are taken into account accuracy may only be to within nearer 4mm.
It may not sound much but it's enough to make all the difference in handling. This way there's no slop, no compromise.
Regulations allow the designers to move the suspension mounting points within a sphere of 20mm, that is in and out, up or down. That means the rally cars have to keep, more or less, the sort of suspension found on the road cars but even if the basic specification is the same there's a world of difference, Take the Ibiza's rear suspension. On the road car it's a simple beam. On this year's Evolution 2 rally car it's a complicated system fabricated from aircraft quality light high tensile steel, with two trailing arms mounted on a beam so the rear suspension is fully independent. Those two arms are braced by 2 Panhard rods stretching across the car to give sideways location. Those rods are allowed even though they are not on the road car because they use location points that can be found on the standard car. Successful race car designers have to do everything the rules allow, an example of the ingenuity needed to win.
Why go independent at the rear? As Chief Mechanic John Down explains, "It gives fewer geometry changes over jumps, with less of the kick back through the car when it lands on one wheel, and it gives a better spread of heat through the tyres. You can even see the difference between the cars fitted with and without it on rallies just on the way they behave."
Even more important on these front-wheel drive only cars is the front suspension. Extremely strong fabricated wishbones (long for tarmac events to give more negative camber) are mounted to a vital component. The new crossmember, which holds suspension and steering rack in place, is quite different from the standard steel pressing. It's made in aircraft spec T45 steel, welded up and heat-treated to withstand the constant enormous shocks generated when the Evo 2 lands nosedown on its front wheels.
Look more closely and you'll see that those shocks are transmitted up directly into the roll cage so the whole structure is sharing the load.
Its one more indication of how much more advanced in this year's Evo 2 car compared with the Evo 1 which itself has brought SEAT so much success. The Evo 2 seems more like a tubular structure with a body around it while the Evo 1 was more like a shell stiffened by a roll cage. On to that new crossmember goes a new steering rack, with far fewer turns of the steering wheel lock to lock than standard, with most drivers liking two and a half. Power assistance is upped thanks to far greater hydraulic pressure from the power
steering pump and the amount of assist is tailored to each driver, usually at the beginning of the season, via different shims in the pump. In the SEAT team, as John Down explains, "Gwyndaf likes nice light steering while Barbara Armstrong likes much firmer steering."
Everywhere you look on this production based class the end result is far removed from any road-going car. John Down again "About the only thing you could buy off the shelf in the parts department would be the glass and headlights." Everything else is different or modified. Take the rear wings; surely they look different? You're right, they are flared to cove the wider track and far larger wheels and are made of lighter gauge steel.
The engine is production based but that gives quite the wrong impression. Although it has to be the same two litres and remain normally aspirated rather than turbocharged it's still quite different from the 16valve 1984cc 150bhp unit found in the Ibiza Cupra Sport road car. The standard block and head have to be retained but the head is reworked with larger inlet and exhaust ports, along with larger valves made in titanium.
Crankshaft and connecting rods are new, and made out of very high strength steel. The rods are also as light as possible, as are the pistons to minimise the reciprocating weight spinning around and help the engine rev as quickly as possible to 9000rpm. Naturally the camshaft timing is nowhere near that on the standard car.
As an example of how much work goes into the engines, the sump alone takes 40 hours to build up. It's full of very complicated baffling to stop the oil draining away from the pump in violent cornering because even a split second's lack of pressure ruins the engine. Race engineers would prefer dry sumping where the oil is pumped around from a separate tank but these cars have to stay closer to road car design.
Other features are just as far away from the production car, such as the £2700 worth of carbon clutch and associated flywheel, or the two rail fuel injection system which can switch from four to eight injectors to produce maximum power. It's no surprise these engines need frequent attention and SEAT are regularly air freighted to the specialist engine builders Mader back in Switzerland for an expensive rebuild, typically after two rallies and a test session.
These engines are extremely valuable assets and they've protected by water-to-oil heat exchangers rather than conventional radiators alone to keep temperatures as steady as possible. Rally teams run two different engine specifications, one with more outright power, (something beyond 270bhp, but no one gives away precise figures in this business), for fast tarmac events where the car might be geared for 125mph. The gravel spec engine in contrast will have less power but more torque, with the car geared for a lower maximum nearer 110mph.
To give the drivers the best chance to exploit all this power the standard five speed gearbox is thrown out and replaced by a Hewland six-speed sequential unit closer in spirit to a motorbike gearbox and the driver only has to move the lever one way to change gear at lightning speed.
It's the interior of the Ibiza which really brings home just how different these cars are, All the standard interior and trim is junked. Extra mouldings are made up to supplement the standard left-hand-drive dashboard moulding to take a huge array of equipment.
There's a large bank of relays on the right, the trip fuses (which the co-driver can reset in a split second when on the go), radio, and trip meter. The driver's given additional information too - a digital rev counter reading beyond 9000rpm.
As Gwyndaf and Barbara will be almost always be too busy to look at that, shifting close to full power with right foot to the floor, there's a reminder light mounted on top of the dash. That indicates when the engine is at full power in each gear and it's time to shift, while there's another to show when the gearbox is in neutral (again as with a motorbike, and vital with a sequential type gearshift for the mechanics as well as the driver). There's even a display to indicate which of the six gears is in use.
As you watch the car take shape in the SEAT Cupra Sport workshop it looks bullet proof but many of these components won't be around long at all, strong as they appear. They are 'lifed' as in the aircraft world, in other words used only for a certain time and then changed regardless of apparent condition because the risk of failure is too great. Driveshafts will only be used once despite being over £1000 each. In the same case with the steering and suspension joints while other parts not automatically lifed are X-rayed and crack tested as a precaution.
With a modern rally car nothing is left to chance but the designers, engineers and mechanics can only do so much. Then it's down to the driver and navigator.