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The use of green hydrogen as a fuel is a promising solution for reducing greenhouse gas emissions from our current fleet of petrol-fueled vehicles. However, achieving zero emissions remains a challenge due to the higher relative air-to-fuel ratio (lambda) required to avoid NOx formation during periods of increased load demand. On the other hand, the capability of hydrogen combustion to use a lean mixture with lower combustion variability presents a great advantage. In such cases, thermal efficiency can be improved by reducing pumping work through leaning the mixture and dethrottling to maintain the same load. This study investigates the efficiency and combustion parameters of hydrogen spark ignition operation while maintaining a constant load at several intake pressure conditions. Tests were conducted on a Ricardo Proteus spark ignition single-cylinder research engine to evaluate the impact of throttle aperture on pumping work and combustion parameters.