 Several of the 'old guard' manufacturers returned to the WSC within the next two years, with each marque adding to the diversity of the series.Under the new rules, it was theoretically possible for normally aspirated engines to compete with the (expensive to maintain) forced induction engines that had dominated the series in the '70s and early '80s.In addition, most races ran for either 500 or 1000 km, usually going over three and six hours, respectively, so it was possible to emphasize the "endurance" aspect of the competition as well.