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[ The challenge and teams | Result | Anoraks' diary | Cat-alysts' diary | Science | Related links ]
In the sport of power-pulling teams have as many as five 2,000hp engines to generate enormous horsepower. They then use a specialised transmission to gear down the power and turn it into lots of torque and, crucially, loads of traction.
Traction can be increased with a greater surface area and added weight. Our teams opted for either a large surface area or weight.
The Cat-alysts went for lots of extra wheels at the back to increase their ground contact. The Anoraks added to their already big ballast to increase the weight over their back axle.
On traditional power-pullers, the tyres have shallow treads so they don't dig into the mud. The idea is to spin the tires as fast as possible (about 80mph) without them digging down and without spraying all the mud in front of the sledge they're trying to pull. As the tyres spin, they expand, increasing their surface area. This expansion is a result of centrifugal force.
Pulling huge loads needs big engines geared to produce loads of torque. Both our teams have gone for diesel engines. Unlike petrol engines, these work by compressing air and injecting fuel at the top of the piston stroke where it ignites without a spark because the air is hot.
The bigger the cylinder, the more air there is inside it and, therefore, the more power it can produce, making diesel engines perfect for a challenge like this.
Size certainly mattered to The Anoraks who opted for a huge lorry and cut and shut it.
They attempted to put all the lorry's pulling power on to the back axle, firstly by stripping away all the extraneous material of the cab and then by strapping a load of barrels over the back axle. By filling the barrels with water, they really weighed the back down.
Finally, they went for a bit of advanced engine tweaking. By retuning the engine's governor, which regulates the amount of fuel going into the engine, they were able to dump a huge amount of fuel into the engine for that final bit of extra poke. Clever stuff but it was a big job and the danger with messing around with the governor is it can make the engine go bang.
The Cat-alysts took an old Fordson Major tractor and whacked in a weighty new engine. After that, the title holders increased the footprint by adding a few more wheels and, for a bit of extra weight, they cunningly filled the wheels with concrete.
It's a classic design and they had the perfect pulling machine, but if they got it wrong, it could tear itself apart.