This Chip improves driveability and also more power (4-5hp). Will work with std engine, but designed for use with ratio rockers arms (1.25-1 or 1.4-1) and std or free flow exhaust. Fits ECU #s 025 906 022 “D” or replacement ECU 025 906 022 “X” (w/O2 sensor). Will not fit ’86-’87 ECUs 025 509 022.