In 1966, the big-block 427 in³ debuted and the L72 427/425 HP was the better of two models offered. Unlike the L36 rated at 390 HP, the L72 had 425 HP. Both cars shared the same power bulge hood which distinguished the cars from the 327 in³.

These cars came with 5500 redline tachometers, whereas the 1966 L78 came with 6500 rpm tachometers. In 1967, again the L36/390 was offered and upgraded with the new 427 big block hood.