 G92 (performance axle ratio) available only on IROC-Z with 5.0 TPI (LB9).All 1987 350 TPI L98 IROC-Zs came standard with the 3.27 BW rear end and everything that was included with G92 but did not have the G92 RPO code because it was not mandatory; this changed in 1988 however when a 2.77 rear was standard and G92 had to be specified to get the 3.27 differential.The IROC-Z was also treated to some small cosmetic changes.