 Bigger, more powerful engines were permitted under homologation rules.The number of valves, ports, and spark plugs were not allowed to be modified from the original configuration.The AAR Toyota team suddenly encountered a daunting problem with the rules when, with Toyota's introduction of the new, fourth generation, Celica for the US market, and the team's first entry into the top-flight GTO category (despite not having won a single GTU title), the team faced the distinct possibility that they would be required to race a front-wheel-drive car, until they managed to persuade IMSA to change the rules, thereby permitting cars to race with something other than their original drivetrain, and therefore with a redesigned chassis.