Fastest JCB on earth

The earth-mover marque is attempting to break the diesel land speed record. John Simister reports on a very British project

The land speed record. Fastest human on earth. Glory and pride and a lot of danger. Currently it stands at a supersonic 763mph, set in 1997 by a virtual jet aeroplane with no wings and bigger wheels. Thrust SSC's driver/pilot was Wing Commander Andy Green, and in August this year he will be attempting a new land speed record in something much closer to the real world.

This time it's the diesel land speed record, using a car driven along by its wheels and not by jet thrust. The present record of 235.756mph was set in August 1973 by Virgil W Snyder in his Thermo King Streamliner, but nowadays Audi's diesel Le Mans race cars aren't far behind that speed. In August, if all goes to plan, the record will hurtle to more than 300mph. And the vehicle to do it will be a JCB.

The JCB Dieselmax, a 9m-long streamliner powered by two highly tuned examples of the JCB444 diesel engine that has powered all kinds of JCB machinery since 2004, is, however, different from your usual digger.

"For 25 years it was the dream of the company founder, Joe Bamford, to build our own engine," says JCB engineering director Dr Tim Leverton. "We started production in 2004, and we've made 10,000 of them so far. Now, to prove we have entered engine manufacturing, we want to use the engine in a record-breaking car. Extreme performance is part of our brand values."

The JCB444 engine - four cylinders, 4.4 litres, designed by the British engineering consultancy Ricardo - comes in many forms to suit its different applications. Normal outputs of the 16-valve turbodiesel are up to 125bhp and 457lb ft of torque with a speed limit of 2,800rpm, but the Dieselmax clearly needs much more than that to break the 300mph barrier. So the capacity is increased to 5.0 litres, and it gains modified pistons, camshafts and fuel injection to increase the flow of fuel and air.

Both an intercooler and aftercooler help to make the intake air denser, and water injection and extra oil jets keep things cool when the two-stage turbocharger is blowing at its maximum 5.2 bar boost (more than turbocharged Formula 1 cars used to have).

The result is an engine with 750bhp, 1,105lb ft of torque, a rev limit of 3,800rpm and an appetite for only the very best high-cetane diesel fuel. And the JCB Dieselmax has two of them. One drives the front wheels, the other the rear wheels, and the driver sits between them. There are two gearboxes as well, linked electronically so there's no danger of one changing gear when the other does not.

As you would expect, aerodynamics are vital. The Dieselmax's shape was designed by Ron Ayers, who also shaped the Bloodhound missile and Thrust SSC. Unlike these two, the Dieselmax won't be reaching supersonic speeds, but even at 300mph there are enough airflow quirks caused by air-compressibility factors to preclude normal wind-tunnel tests. So Ayers used computational fluid dynamics, which means the first time he'll know if the Dieselmax really works will be during the first test runs at RAF Wittering.

"The underfloor shape is critical," explains Leverton, "because we want neutral lift and no downforce. There are no radiators because they generate drag. Instead we have an ice-primed cooling system for two engines and two intercoolers that must last for 110 to 120 seconds."

JCB's Dieselmax will reach about 200mph on Wittering's 2.5-mile runway, but Leverton will alter the step-up ratio between engines and gearboxes so that the engines can run at full effort. The engineers will be looking very hard at the airflow characteristics around the front wheels, because the record attempt is to be on the Bonneville salt flats in Utah - the world's largest dead-flat space. The powdery surface causes salt spray, and the idea is to divert that away from the rear wheels so it doesn't spoil traction.

One of the heartwarming things about the JCB Dieselmax project is that it's entirely British. Richard Noble, the driving force behind the Thrust SSC record-breakers, is advising Leverton's team, and Leverton himself has the unusual distinction of having helped to engineer the remakes of three iconic British designs: the Mini, the Range Rover and the Rolls-Royce Phantom. The makers of those cars were foreign-owned, however. This time it's truly a home-team effort.