I saw a movie back in the 80's one late night on one of the movie channels and will never forget it. I was a teenage boy and loved the soft-core/nudity that the late night movies had to offer. I think this movie made me the boob man I am today. Anyway the movie was about a female cop/detective and she drove a Trans am or something. She was a brunette, very slim and had very, very, very large breasts for a woman her size. There was a shower scene that I vividly remember where she and another woman (black) where showering and each had amazing breasts. It was a poorly shot movie and the script was just as bad. I think the point of the movie was to showcase the woman's breasts.
Sounds like STACEY.
http://www.imdb.com/title/tt0070727/