Dieselmax

Fast diesel road cars, a diesel Le Mans winner. What next, a diesel Land Speed Record car? That’s how JCB decided to showcase its skills, with the fastest man in the world at the wheel
Words: Keith Howard. Photography: JCB

On 22 and 23 August this year at Bonneville’s famous salt flats, Andy Green added a second Land Speed Record to his CV when he drove JCB’s Dieselmax to new FIA-approved records for a diesel-powered car of 328.767 and then 350.092mph, pulverising Virgil Snyder’s 1973 record by over 114mph. Bankrolled by JCB, powered by Ricardo-modified JCB engines, shaped by Thrust SSC aerodynamicist Ron Ayers and designed by Coventry-based Visioneering Ltd, Dieselmax is remarkable not just for its achievement but for the fact that it was created in just 10 hectic months starting in late September 2004. Chief engineer John Piper, who assembled the small design team at Visioneering and has extensive racing experience including time at Reynard Special Vehicle Projects, talks here of some of the key aspects of the car’s design and development.

Layout

“Because the powertrain is quite big, to get an acceptable sectional area for the car you have to lie the engine on its side. As soon as you have two engines, you can’t put both behind the driver and still drive all four wheels without a driveshaft coming round the driver somehow. So it falls out naturally that you have an engine and transmission at either end and the driver in the middle. That was pretty much established by JCB and Ricardo when Visioneering came to the project.”

Brakes

“From the start we decided to have brakes that could stop the car even if the ‘chutes failed. Parachute failure is not uncommon — we had two at Bonneville and split the reserve. We’d been told that we wouldn’t need any brakes, but we chose to ignore that advice and were glad we did. We first looked at using an F1 brake but that just wasn’t big enough to stop the car, while an Indycar brake was too big to fit in a 15-inch rim. So we designed our own. It uses a single carbon-carbon rotor which is driven on its outside diameter by the wheel. There are two carbon disc stators which act as pads, with a single-sided caliper that slides them along a splined tube into contact with the rotor. This arrangement allowed us to get the brake as far outboard as possible, which in turn permitted the steering geometry we wanted.”

Aerodynamics

“Ron Ayers was already on board and working with Mike Turner of JCB’s design team on a surface model. We would create a basic package, Mike would build a surface around it under Ron’s direction and Ron would then analyse it using CFD [computational fluid dynamics]. We would then import the surface into our CAD program and begin the body engineering before gathering around the screen with Ron, looking at what poked through the surface and deciding what was worth trying to get beneath it. It was an iterative process, with Ron in charge of the aerodynamic decisions. We twice lowered and narrowed the car to achieve the figures we wanted [Cd 0.174, CdA 0.152 square metres]. I wish we could have had longer to perfect the car’s shape but at that time we didn’t know what the tyres were going to be, and that was a major factor in the car’s design.”

Chassis

“We never seriously considered using anything other than a steel spaceframe chassis. When you have a tonne and a half of powertrain, you have to mount two turbos per engine that weigh 50kg and run at 900 deg C, and you want the chassis to be stiff enough to achieve a torsional resonance frequency well above the wheel frequency, steel is good stuff. We had a lot of help from Corm: we’d gone through its catalogue and found the sections we wanted but they were all too thick, so their representative did a sweep of all their rolling mills worldwide and found some thinner gauge sections for us. The chassis frame weighs only 250kg, which is quite an achievement for the load it has to carry and the torsional stiffness we required. We created a monocoque carbon tub for Andy Green to sit in, partly because it is a good way of excluding any fluids in a crash. It also provides all the surfaces to mount the pedals, dashboard and seat. We bonded that into the steel structure, and bonded carbon panels each side of the two-inch steel spaceframe with honeycomb in the middle, in order to create a stiff perimeter structure around the cockpit opening.”

Tyres

“In the end we used a Goodyear Eagle Frontrunner tyre rated at 300mph at 17001b of load, which is about the static corner weight of the car. We wanted to go higher than 300mph so we had Lotus Engineering build a free spin rig, but even aircraft tyres failed, whereas we successfully spun the Frontrunners up to 400mph. We realised then that the only option we’d got was the 23-inch Goodyear, and that the car would have to be limited to the speed at which it could be validated. David Brown of JCB found us a suitable test facility at the Wright-Patterson air force base in Dayton, Ohio where they developed the Space Shuttle tyre. We replicated a run on the salt which validated the tyres for a single pass at 350mph. They were blistering on the third run so we decided that if we got to 350mph we would change tyres at the turnaround. This is what we did, even though at Bonneville we saw no blistering at all. If it weren’t for the tyre limitation we could have gone a lot faster. But whether we go back and try for this next year is up to JCB — no decision has been made yet.”