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98 would have an Auburn 'posi',2000 would have a Torsen 'posi',would have no effect on 'channel'.
since you didn't give any specs on the cars,
98Z A4 could be 2.73 or 3.23,98Z M6 would be 3.42
2000 Firehawk A4 would be 3.23,M6 would be 3.42