Nitpicky enough to please film-history nerds but lively in a way that should tickle the merely curious, Elijah Drenner’s informative history of exploitation movies is likely to end up preaching only to the converted. Pity, because while American Grindhouse relies heavily on static bloviation (John Landis makes for a particularly talky head), it also deftly traces the lineage of cheapjack, self-distributed cinematic slop to the enduring indie boom. Drenner covers all the bases in his wide-ranging doc, from roadshow “hygiene” crypto-porn to nudies, roughies, biker flicks, and beyond. Schlock luminaries like the swaggering, very funny Fred Williamson and gore impresario Herschell Gordon Lewis turn up to add color (and, in Lewis’s case, severely overestimate their influence), and a few clued-in critics drop in to provide context. Clips also abound, and Drenner doesn’t skimp on money shots: The climax of producer Kroger Babb’s 1945 birth-of-a-baby megahit Mom and Dad is here in all its clinical ickiness; suffice it to say that Babb is no Stan Brakhage. Yet for all its thoroughness, American Grindhouse has an unavoidable bandwagon-y feel, as if it were still in production after the junk-movie boosters whose lead it follows (Quentin Tarantino and Robert Rodriguez, basically) had already moved on.