How do I identify which LS engine I have?

Start with the RPO code, not the displacement. GM put a Service Parts Identification sticker (usually in the glovebox) listing three-character RPO codes; the engine code (e.g., LM7, LQ4, L33) is on it.

The VIN helps, with a catch: the 8th character of the VIN identifies the engine, but the same engine can have a different 8th digit on a car vs. a truck vs. an SUV. Use it to narrow down, then confirm with the RPO sticker. Examples from GM truck applications: LM7 = T, LQ4 = U, LQ9 = N, L33 = B, LR4 = V, LY5 = J, LMG = 0, LC9 = 3.

Other clues on the engine itself:

• Block material: iron (most truck 4.8/5.3/6.0) vs. aluminum (car engines, some trucks: L33, LH6, LC9, LS2, LS3…).
• Crank reluctor: 24x (black sensor) on 1997–2006 engines, 58x (gray sensor) on 2006+; this also decides which ECU/harness works.
• Head casting number (e.g., 241, 243, 799, 706, 862, 317, 823) tells you the head family.

See our donor engine ID chart for every 4.8/5.3/6.0/6.2 with its VIN code and common donor vehicles.