Money From Home (1973)

Busy porn thesp Marc Brock stars (uncredited) as Mark (spelling inferred), visiting Chicago with 2 pals, who has a phone number for Mary (Connors) and invites her to bring 2 friends over in an hour. When they arrive the next hour is the 6 performers having sex, with no preamble and even minimal small talk. It's that kind of 1-day wonder picture.