Abstract: An exhaust header modeling apparatus includes a plurality of interchangeable straight and curved short cylindrical segment members which are selectively and releasably joined together end-to-end manually and rotated relative to one another to form a full-scale three-dimensional model of a desired engine exhaust header design or configuration. The segments are provided in sets having outside diameters corresponding to the outside diameters of conventional exhaust header tubing and have a circumferential scale at each end to visually determine the relative rotation between one segment and an adjoined segment. When assembled, the model provides optimum header layout and pathways to accurately fit within an available space, and provides accurate dimensions to aid in cutting forming sections of the exhaust headers from pre-bent metal tubing sections and the proper relative rotation between them.