Why JCB? The company's engineering director, Tim Leverton, describes it as the logical extension of the dream held for many years by the digger-maker's late founder, Joe Bamford, for JCB to build its own engine. 'We started production of our engine in December 2004,' says Leverton. 'Dieselmax proves we have entered engine manufacturing, and extreme performance is part of our brand values.'

The JCB Dieselmax has two four-cylinder turbodiesels based on the 4.4-litre JCB444 engine. Bore and stroke are enlarged to give a 5-litre capacity, and other modifications include camshaft timing, piston and combustion-chamber shape, uprated oil jets to cool the pistons and two-stage turbochargers with ice-cooled intercoolers and aftercoolers. Water injection helps further to keep things cool. The total output is 750bhp with 1105lb ft of torque at 2500rpm.
Each engine drives its own axle, and Andy Green sits between the engines. The fuel tank, incidentally, carries just nine litres of diesel fuel, proving that even a record-breaker can be frugal.

The Dieselmax's bodywork was designed by Ron Ayers, who shaped both the Bloodhound missile and Thrust SSC. (Project Thrust mastermind Richard Noble is a consultant on this project.) The body is of carbonfibre, covering a square-tube spaceframe chassis.

'The shape is long and low,' Leverton explains, 'but not as thin as we'd like because it's driven by the integration of the chassis and the engine. The underfloor shape is critical because we want neutral lift and no downforce. There are no radiators because they generate drag.' (Hence the ice-cooling.)

'The ride height is critical, as is the shape of the inner wheelarches at the front,' adds Leverton, pointing out that there will be salt spray at Bonneville, making clever wheelarch aerodynamics vital to divert the front wheels' spray away from the rear wheels to maximise traction on the powdery surface.

Surprisingly, there has been no wind-tunnel testing - sufficient air speed can't be generated to create the air-compressibility effects found at 300mph. Instead it's all been done by computational fluid dynamics calculations, so there'll be anxious moments when the Dieselmax has its first test runs at RAF Wittering. 'It's a 2.5-mile runway, so we won't get beyond 200mph,' says Leverton. 'but we'll alter the gearing so we can run it at full load.'

The JCB Dieselmax will be an extraordinary sight that will make an extraordinary sound. If it's successful, it will be a fine tick in the box for both Leverton and JCB.