 The LB9 was available only on the Z28 and the IROC-Z model with the TH700-R4 automatic transmission.A total of 205 IROC-Zs equipped with the LB9 305 with the G92 (Performance Axle Ratio) option were made in 1985.The G92 option upgraded the rear axle gear ratio from 3.23 to 3.42.