Mercruiser Block ID Codes – Big Block V8
The specific model/vintage of Big Block V8 Mercruiser Engine can be determined by looking at the last letters of the engine code which is stamped by General Motors at the time of assembly on all complete Marine Longblocks. If the serial number and/or model decals are missing, the Engine code will help to determine the engine model. Refer to the drawing below for the specific engine code location on your Mercruiser Engine.
Information you need from the engine code, example M01187MH. 7=General Motor’s model year in this case 1997, BUT this could also be 1987 or 1977. MH = Type of engine. The 350 cid V8 Mercruiser models 5.7L, 350 Mag Mpi, Black Scorpion Ski, etc.
GM V8 454 cid (7.4L) Mark IV – Sterndrive Models (LH rotation), flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 330 TR/TRS | XS | 1977–1981, Mercury transmission | 14 (356) |
| 330 (B–W) | XY | 1982–1987, TR/TRS, Borg–Warner transmission | 14 (356) |
| 454 Mag | XS | 1986–1988, Alpha, GM 4–bbl intake | 14 (356) |
| 7.4L Mag | XS | 1988, Alpha, GM 4–bbl intake | 14 (356) |
| 454 Mag | XA | 1988–1992, Bravo, GM hi–rise intake | 14 (356) |
| 7.4L | XW | 1988–1992, Bravo, T05209XW, start 4 bolt main, GM4–bbl intake | 14 (356) |
Inboard Models (rotations shown), flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 330 | XN (XR) | LH (RH), 1977–1979 | 14 (356) |
| 330 | XY (XZ) | LH (RH), 1980 | 14 (356) |
| 340 | XY (XZ) | LH (RH), 1981–1984, 1985–1987 | 14 (356) |
| 340 | XYY(XZZ) | LH (RH), 1985 | 14 (356) |
| 350 | XB (XC) | LH (RH), 1974–1976 | 14 (356) |
| 7.4L | XY (XZ) | LH (RH), 1988–1992. T05209XY (T05209XZ), start 4 boltmains | 14 (356) |
| 7.4L | XR | RH, 1992 | 14 (356) |
GM V8 454 cid (7.4L) Mark IV – Sterndrive Models (LH rotation), flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 330 TR/TRS | XS | 1977–1981, Mercury transmission | 14 (356) |
| 330 (B–W) | XY | 1982–1987, TR/TRS, Borg–Warner transmission | 14 (356) |
| 454 Mag | XS | 1986–1988, Alpha, GM 4–bbl intake | 14 (356) |
| 7.4L Mag | XS | 1988, Alpha, GM 4–bbl intake | 14 (356) |
| 454 Mag | XA | 1988–1992, Bravo, GM hi–rise intake | 14 (356) |
| 7.4L | XW | 1988–1992, Bravo, T05209XW, start 4 bolt main, GM4–bbl intake | 14 (356) |
Inboard Models (rotations shown), flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 330 | XN (XR) | LH (RH), 1977–1979 | 14 (356) |
| 330 | XY (XZ) | LH (RH), 1980 | 14 (356) |
| 340 | XY (XZ) | LH (RH), 1981–1984, 1985–1987 | 14 (356) |
| 340 | XYY(XZZ) | LH (RH), 1985 | 14 (356) |
| 350 | XB (XC) | LH (RH), 1974–1976 | 14 (356) |
| 7.4L | XY (XZ) | LH (RH), 1988–1992. T05209XY (T05209XZ), start 4 boltmains | 14 (356) |
| 7.4L | XR | RH, 1992 | 14 (356) |
GM V8 454 cid (7.4L) Gen V – Sterndrive Models (LH rotation), 4 bolt mains, flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 7.4L | XW | 1992–1996, 1XW, start Gen V, no mechanical fuelpump pad on cylinder block, GM 4–bbl intake | 14 (356) |
| 7.4LX MPI | UC | 1996, MerCruiser MPI intake | 14 (356) |
| 7.4L PT Bravo 3 | UW | 1993, cast pistons, start GM hi–rise intake | 14 (356) |
| 7.4L PT Bravo 3 | UB | 1993–1994, start forged pistons | 14 (356) |
| 7.4L PT Bravo 3 | XX | 1994–1996, start new design cast pistons | 14 (356) |
| 454 Mag | XA | 1992–1996, 2XA, start Gen V, no mechanical fuelpump pad on cylinder block, GM hi–rise intake | 14 (356) |
| 454 Mag | XAA | 1995, GM hi–rise intake | 14 (356) |
| 454 Mag MPI | UA | 1994–1996, MerCruiser MPI intake | 14 (356) |
Ski Models (LH rotation), 4 bolt mains, flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 454 Mag MPI | UA | 1994–1996, no mechanical fuel pump pad on cylinderblock, MerCruiser MPI intake | 14 (356) |
Inboard Models (LH rotation), 4 bolt mains, flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 7.4L | XY | 1992, 2XY, start Gen V, no mechanical fuel pump pad oncylinder block, GM hi– rise intake | 14 (356) |
| 7.4L MPI | UD | 1995–1996, MerCruiser MPI intake | 14 (356) |
GM V8 454 cid (7.4L) Gen VI with Roller Lifters – Sterndrive Models (LH rotation), 4 bolt mains
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 7.4L | XW | 1996–1997, 6WX, start Gen VI, GM 4–bbl intake | 14 (356) |
| 7.4LX EFI | UJ | 1996–1997, start Gen VI, GM TBI intake | 14 (356) |
| 7.4LX MPI | UC | 1996–1997, 6UC, start Gen VI, Mer‑ Cruiser MPIintake | 14 (356) |
| 454 Mag | XA | 1996–1997, 6XA, start Gen VI, GM hi–rise intake | 14 (356) |
| 454 Mag MPI | UA | 1996–2001, 6UA, start Gen VI, MerCruiser MPI intake | 14 (356) |
Ski Models (LH rotation), 4 bolt mains
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 454 Mag MPI | UA | 1996, 6UA, start Gen VI, MerCruiser MPI intake | 14 (356) |
Inboard Models (LH rotation), 4 bolt mains
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 7.4L | XY | 1996–1997, 6XY, start Gen VI, GM 4–bbl intake | 14 (356) |
| 7.4L EFI | UK | 1996–1997, 6UK, start Gen VI, GM TBI intake | 14 (356) |
| 7.4L MPI | UD | 1996–1997, 6UD, start Gen VI, Mer‑ Cruiser MPI intake | 14 (356) |
| 454 Mag MPI | UF | UF 1998–2001, Gen VI, MerCruiser MPI intake | 14 (356) |
GM V8 454 cid (7.4L) L29 – Sterndrive Models (LH rotation), 4 bolt mains, roller lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 7.4L MPI | XW | 1998–2001, 8WX, start L29, GM MPI intake | 14 (356) |
Inboard Models (LH rotation), 4 bolt mains
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 7.4L MPI | XY | 1998–2001, 8XY, start L29, GM MPI intake | 14 (356) |
GM V8 496 cid (8.1L) – Sterndrive Models (LH rotation), 4 bolt mains, roller lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 496 Mag | XW | 2001–UP, 1XW, start 496 cid, GM MPI intake | 14 (356) |
| 496 Mag | WW | 2004 Changed intake manifold gasket and cylinderhead machining | 14 (356) |
| 496 Mag | ZW | 2004 Changed piston pins to floating type | 14 (356) |
| 496 Mag | XW | 2005–UP Returned to XW nomenclature | 14 (356) |
| 496 Mag HO | XA | 2001–UP, 1XW, start 496 cid, GM MPI intake | 14 (356) |
| 496 Mag HO | WA | 2004 Changed intake manifold gasket and cylinderhead machining | 14 (356) |
| 496 Mag HO | ZA | 2004 Changed piston pins to floating type | 14 (356) |
| 496 Mag HO | XA | 2005–UP Returned to XA nomenclature | 14 (356) |
Inboard Models (LH rotation), 4 bolt mains, roller lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 8.1S | XY | 2001–UP, 1XY, start 496 cid, GM MPI intake | 14 (356) |
| 8.1S | WY | 2004 Changed intake manifold gasket and cylinder headmachining | 14 (356) |
| 8.1S | ZY | 2004 Changed piston pins to floating type | 14 (356) |
| 8.1S | XY | 2005–UP Returned to XY nomenclature | 14 (356) |
| 8.1S HO | XF | 2001–UP, 1XF, start 496 cid, GM MPI intake | 14 (356) |
| 8.1S HO | WF | 2004 Changed intake manifold gasket and cylinder headmachining | 14 (356) |
| 8.1S HO | ZF | 2004 Changed piston pins to floating type | 14 (356) |
| 8.1S HO | XF | 2005–UP Returned to XF nomenclature | 14 (356) |
GM V8 502 cid (8.2L) Mark IV – Sterndrive Models (LH rotation), 4 bolt mains, flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 502 Mag | FJ | 1990–1992, GM hi–rise intake | 14 (356) |
| 502 Mag | FH | 1992, some inboards converted to MCM this year only | 14 (356) |
Inboard Models (LH rotation), 4 bolt mains
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 8.2L | FH | 1990–1992, GM hi–rise intake | 14 (356) |
GM V8 502 cid (8.2L) Gen V – Sterndrive Models (LH rotation), 4 bolt mains, flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 502 Mag | FJ | 1992–1993, 2FJ, start Gen V, no mechanical fuelpump pad on cylinder block, GM hi–rise intake | 14 (356) |
| 502 Mag MPI | FJ | 1993, MerCruiser MPI intake | 14 (356) |
| 502 Mag MPI | HJ | 1993–1996, MerCruiser MPI intake | 14 (356) |
Inboard Models (LH rotation), 4 bolt mains, flat lifters
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 8.2L | FH | 1992–1996, 3FH, start Gen V, no mechanical fuel pumppad on cylinder block, GM hi–rise intake | 14 (356) |
| 8.2L MPI | HH | 1996, MerCruiser MPI intake | 14 (356) |
GM V8 502 cid (8.2L) Gen VI with Roller Lifters – Sterndrive Models (LH rotation), 4 bolt mains
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 502 Mag MPI | HJ | 1996–2001, 6HJ, start Gen VI, MerCruiser MPI intake | 14 (356) |
| 8.2L MPI | HH | 1996–2001, 6HH, start Gen VI, Mer‑ Cruiser MPIintake | 14 (356) |
Sterndrive and Inboard Models (LH rotation), 4 bolt mains
| Model | GM Code | Comments | Flywheel Diameter in. (mm) |
| 8.2L MPI | HH | 1996–2001, 6HH, start Gen VI, Mer‑ Cruiser MPI intake | 14 (356) |