Between them, the customer teams put up a competent challenge to Porsche. The North American Racing Team (NART) had three entries. The Penske team, very competitive at the American rounds of the championship, arrived on one of the NART entry tickets. Their chassis was made by Holman & Moody and the engine prepared by Can-Am V8 specialist Traco (claiming 614 bhp). A number of quick-change modifications were added for wheels, brakes and refuelling to save valuable minutes in the pits. The blue, Sunoco-sponsored, car was driven by Mark Donohue/David Hobbs. The regular NART 512M also had a Traco engine and was driven by Sam Posey/Tony Adamowicz. And there was an open-top, spyder, version was for Masten Gregory/George Eaton.