As Ty stated that's the "classic" firing order for an inline six. Any V6 (B1: 1-3-5, B2: 2-4-6) has 3 "shared" crankpins- cyl 1/2, 3/4, 5/6, so when 1 is at TDC, 2 CAN't be at TDC at the same time. The Firing Order for a V6 is either 1-2-3-4-5-6 or 1-6-5-4-3-2... Login to read more.