At 654 km/h, most aircraft would already have been airborne long before. Andy Green’s job was the opposite: keep four wheels firmly on the Bonneville Salt Flats while pushing a hydrogen-powered machine to a new world speed record.

The 64-year-old Briton, who in 1997 became the first and so far only person to break the sound barrier on land, drove the JCB Hydromax to an official two-run average of 406.320 mph, or 653.9 km/h.

The result is not only a new benchmark for hydrogen combustion. It makes Hydromax the fastest hydrogen-powered land vehicle of any kind.

BMW H2R record

The previous FIA record for a hydrogen internal-combustion car had stood since 2004, when BMW’s experimental H2R reached 298.5 km/h. The streamlined BMW used a 6.0-liter V12 derived from the 760i and produced around 285 hp.

BMW recorded a peak of 302.4 km/h during the program, which resulted in nine hydrogen records. Hydromax is therefore more than 355 km/h faster and roughly 2.2 times as quick.

Faster than a fuel-cell car too

Perhaps more significant is that Green also surpassed the fastest hydrogen fuel-cell vehicle. In 2009, the Venturi Buckeye Bullet 2, developed with Ohio State University, reached 303.025 mph, or about 487.6 km/h, at Bonneville.

The technologies are fundamentally different. The Buckeye Bullet converted hydrogen into electricity in a fuel cell and used that electricity to power electric motors. BMW’s H2R and JCB’s Hydromax burn hydrogen directly inside an internal-combustion engine.

Hydromax is another 166 km/h faster than the fuel-cell record. Green has therefore become the fastest person ever propelled on land by hydrogen, regardless of how that hydrogen is converted into motion.

His outright land-speed record remains in another league. In 1997, Green drove the twin-jet ThrustSSC to 1,227.985 km/h, becoming the first driver to break the sound barrier on land officially. In 2006, he also drove JCB’s Dieselmax to 563.4 km/h.

Keeping it from flying

Producing enough power is only part of the challenge. At 654 km/h, the bigger problem is preventing the car from becoming unstable or even airborne.

Aircraft do not fly simply because they reach a certain speed. Their wings are shaped to create lift. Hydromax is designed to do almost the opposite. Its body must minimize drag while producing as little unwanted lift as possible.

Aerodynamic forces increase roughly with the square of speed. A small change in pitch or airflow that would be insignificant at normal road speeds can become enormous at more than 600 km/h. If air starts getting underneath the nose, stability can disappear very quickly.

Hydromax is therefore exceptionally long, narrow, and low. Its two engines are mounted on their sides to reduce frontal area and lower the center of gravity. A large vertical rear fin keeps the car pointing straight, while a ventral strake underneath adds stability.

Even the salt matters. The underside has been shaped to push salt away instead of allowing it to accumulate beneath the body and disturb the airflow.

Green has only a few degrees of steering movement available and makes minute corrections at speed. Once through the timed section, parachutes provide the initial braking.

Not a rocket on wheels

Despite its appearance, Hydromax is not a jet or rocket car. Unlike ThrustSSC, whose jet engines produced thrust directly, Hydromax is genuinely wheel-driven.

Two heavily modified 4.8-liter JCB four-cylinder engines drive the front and rear axles through separate six-speed sequential transmissions. Together, they produce around 1,600 hp.

Hydrogen is mixed with air and burned inside the cylinders using spark ignition. The car carries hydrogen but takes the oxygen needed for combustion from the atmosphere. A rocket, by contrast, carries both its fuel and oxidizer.

That distinction is important because JCB is not developing hydrogen combustion for racing cars. The British manufacturer has invested around £100 million in hydrogen engines for excavators, loaders, and other heavy machinery.

Performance is not efficiency

JCB argues that very large batteries can become problematic for machines working long shifts, often far from high-power charging infrastructure. Hydrogen combustion can retain much of the familiar engine architecture while allowing rapid refueling.

Hydromax is therefore as much an industrial technology demonstration as a speed-record machine. If a hydrogen engine derived from heavy machinery can propel a car beyond 650 km/h, JCB can convincingly argue that lack of performance is not hydrogen combustion’s problem.

But the record does not prove that hydrogen is the most efficient or economical solution. Producing, compressing, transporting, and storing hydrogen requires substantial energy, and its climate benefit depends heavily on how the hydrogen itself is produced.

Hydrogen combustion produces no CO2 from the fuel itself, but high-temperature combustion can still generate nitrogen oxides.