Race cars use aerodynamic downforce to reduce the lap times by increasing grip. Diffusers, upswept ramps located at the rear of a vehicle, are often used to enhance downforce. This investigation proposes a novel LPT facility featuring HFSB, LED illumination, and high-speed cameras to characterize the flow inside automotive diffusers. An RC car, fitted with a custom floor and diffuser, traverses a region of seeded air following the Ring of Fire methodology. Underground cameras view the car through a transparent panel, providing unparalleled optical access to the diffuser of the car. The on-site construction of the setup and the intrinsically realistic interaction with the ground, contribute to realism and fidelity while potentially reducing testing costs associated with wind tunnel operation. The setup was shown to be a valid alternative to conventional testing grounds to capture separation, 3D flow evolution and differences in the flow field between the diffusers with varying angles. The 15° diffuser led to the largest velocity (u/U=1.3) under the car, the 10° diffuser produced the most downforce overall while the 20° diffuser showcased the most prominent separation, heavily affecting its ability to sustain low pressures under the car. The results highlighted the impact of the tyres in disrupting the mechanism of downforce generation through mass flow leakage through the sides of the car.