Aerodynamics of the 1996 Subaru WRX STI

Overview

The 1996 Subaru WRX STI is recognized as one of the most successful rally cars and was considered a supercar.
A common issue with the vehicle was its downforce, leading to the addition of a rear wing.

Front Lip: Although small, it helps accelerate airflow under the car, aiding stability at higher speeds.
Underbody Flow: Performs well and the diffuser is surprisingly effective despite downforce issues.
Rear Window: Major problem due to sharp downward slope, causing flow separation. This issue was also present in its rival, the Mitsubishi Evo.
Rear Wing Position: Positioned too low, affected its effectiveness due to being in the wake of the rear window.
Windshield Shape: The flat design leads to fast-moving airflow causing drag.
Pressure Plot Findings:
- Low pressure over the roof contributes to lift, despite good low pressure at the front and back.
- Roof acts like a wing, generating unwanted lift.
Potential Solutions:
- Sleeker roof design could help reduce lift and drag.
- A more sloped hood might alleviate pressure issues.
Front Design: Blunt and blocky, contributing to high drag.
Overall Downforce: Rear wing generates some downforce, but flow is unsteady and varies, affecting performance.

Comparative Analysis: Similar behaviors in front underbody, windshield flow, and roof pressure.
Wake Characteristics: Without the rear wing, the flow is not kicked up as much, showing marginal differences.
Lift Coefficients:
- With rear wing: 0.01 (essentially neutral).
- Without rear wing: 0.05 (indicates lift).
Wake Stability: Suggests that the rear wing helps stabilize flow and reduces wake size.
Vortex Production: Side mirrors produce significant drag, and without the rear wing, fewer vortices are generated at the rear.
Drag Coefficient:
- With rear wing: 0.36
- Without rear wing: 0.37

Original WRX faced lift problems, prompting the investigation of a larger front splitter for aerodynamic improvement.
A video on this topic is available on Patreon for further insights.