Engine Serial Number does NOT Match Vehicle Identification Number
Short answer: The engine “serial” (Unit) number and the VIN are two different numbers and will never match. But starting in 1968, a partial VIN was also stamped on the block — on the front lower face near the timing cover/harmonic balancer — and that should match your car’s VIN. If it does, it’s the original engine for the car.
- The Engine Unit Number is an internal plant sequencing number (used to match an engine to a specific car). It appears on the Broadcast Sheet and Billing History, with no tie to the VIN — cars with very close VINs can have unit numbers hundreds or thousands apart.
- The block VIN is hard to see — remove the lower radiator hose at the water-pump housing, or use a mirror and light down by the harmonic balancer.
- Engines arrived at final assembly fully assembled, stamped with a two-letter usage/application code (plus a white-and-red label) so the line installed the right parts; the VIN was stamped just before the engine went into the car.
- Service bulletins reference engine unit numbers (e.g., 1967 Ram Air engines: 1st type through unit #646615, 2nd type from #646616).
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Content last modified: June 13, 2026 at 10:06 am
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Hey guys I have a 1972 455 H.O. hat came in a trans am , is there anyway I can use the engine number to try to find the body?