This study investigates the effect of heat treatment on the torsional properties of AISI-H11 modified (H11 mod) torsion bar steel, a high-strength material used in demanding applications. This study focuses on optimizing heat treatment parameters, specifically tempering temperatures ranging from 540°C to 620°C, to enhance torsional performance. A hyperbolic model was employed to accurately fit the torque-angle curve in the plastic deformation region, providing reliable shear stress estimates. Microstructural analysis revealed a lath martensitic matrix with globular carbide precipitates and trace amounts of retained austenite. Mechanical testing, including hardness, tensile, and torsion tests, revealed a strong correlation between tempering temperature and torsional properties. The results show that a maximum hardness of 49.6 HRC is achieved after oil quenching from 1010°C, followed by double tempering at 540°C. The torsion test results demonstrated a decline in the maximum shear stress from 1145 MPa at 540°C to 889 MPa at 620°C, indicating reduced strength at higher tempering temperatures, possibly due to the increase in the number of precipitated carbides and the decrease in the content of alloying elements in the solid solution. Conversely, the maximum shear strain increased from 0.2187 to 0.2803, suggesting improved ductility. These findings highlight the optimal tempering condition at 540°C for applications requiring high torsional strength, with implications for aerospace and off-road vehicle systems.