PORSCHE RACING HISTORYMark Altman (USA)
1981 : Watkins Glen 6 Hours - 2nd in class
12 July 1981 - Watkins Glen 6 Hours - World Championship for Drivers and Makes
| No. | Car | # | Class | Drivers | Entrant | Pos | Class | Grid | Notes |
| 13 | Porsche 911 Carrera | GTO | Steve Southard (USA)/Mark Altman (USA)/Gary Altman (USA) | Southard Motor Racing (USA) | 9th | 2nd | 25th | 146 laps |
30 August 1981 - Mid-Ohio 500 km - Non Championship Race
| No. | Car | # | Class | Drivers | Entrant | Pos | Class | Grid | Notes |
| 40 | Porsche 911 Carrera | Gr.4 | Steve Southard (USA)/Mark Altman (USA) | Southard Motor Racing | 11th | 6th | 24th | 115 laps |