The HPD ARX-04b is an LMP2 race car designed and built by Wirth Research for Honda Performance Development.

Two cars were delivered to its sole customer, Extreme Speed Motorsports, in December 2014, where it soon began testing.

Following the disappointment of Daytona, Extreme Speed Motorsport decided to take time to test the car further, opting to race the older HPD ARX-03b at Sebring.

HPD continued to test and develop the car, to try and resolve aerodynamic problems and improve its performance.

The car was later used by Shank to test the 2017 Continental tyres for the upcoming season [6][7][8] The ARX-04b made a racing return at the 2023 Silverstone Festival Masters Endurance Legends event, driven by Steve Tandy.