Engine production code

Reference Details

Common issue

A correct-type Nailhead with an unrelated production code or date represented as the original engine. · 1965 Buick Skylark Gran Sport 401 Nailhead

Confidence

documented · 1965 Buick Skylark Gran Sport 401 Nailhead

Correct value

LR identifies the 1965 Skylark Gran Sport 400/401 four-barrel engine at the model-reference level. · 1965 Buick Skylark Gran Sport 401 Nailhead

Where to check

Production code stamped on the right front of the engine block; verify the adjacent serial information and casting dates. · 1965 Buick Skylark Gran Sport 401 Nailhead

Common issue

A correct-type Nailhead with an unrelated production code or date represented as the original engine. · 1966 Buick Skylark Gran Sport 401 Nailhead

Confidence

documented · 1966 Buick Skylark Gran Sport 401 Nailhead

Correct value

MR identifies the standard 325-hp 401. A claimed late L76 must also match the automatic-only Quadrajet specification and car-specific production-code, date, and paperwork evidence. · 1966 Buick Skylark Gran Sport 401 Nailhead

Where to check

Production code and engine serial stamped at the front of the Nailhead block near the right cylinder head; verify dates and the VIN-derived serial. · 1966 Buick Skylark Gran Sport 401 Nailhead

Common issue

A 340 or other 1967 Buick V-8 engine-code stamping treated as a GS 400 engine without the NR engine-code evidence and car-specific corroboration. · 1967 Buick GS 400

Confidence

documented · 1967 Buick GS 400

Correct value

A 1967 GS 400 engine-code check should find engine production code NR for the GS 400 400 CID, 340 hp, 4BC engine; production-date and original-to-car validation still require car-specific evidence. · 1967 Buick GS 400

Where to check

Stamped on the right side of the engine block as part of the engine production code. · 1967 Buick GS 400

Common issue

A standard 455 or replacement block represented as Stage 1 without code/date/VIN support. · 1971 Buick GSX Stage 1

Confidence

documented · 1971 Buick GSX Stage 1

Correct value

1971 GS Stage 1 455 engine appears as TS in Buick engine-code table. · 1971 Buick GSX Stage 1

Where to check

455 CID V-8 production code pad between rear spark plugs and left exhaust manifold; VIN derivative/serial stamping also present. · 1971 Buick GSX Stage 1

Common issue

A replacement or base 455 block may not carry the WS production code or VIN-derivative serial match. · 1972 Buick GS Stage 1

Confidence

documented · 1972 Buick GS Stage 1

Correct value

WS for 1972 455 Stage 1 GS engine · 1972 Buick GS Stage 1

Where to check

455 engine production code stamped between the left exhaust manifold and the two rear spark plugs; engine serial number on front of right cylinder bank · 1972 Buick GS Stage 1

Common issue

Earlier Stage 1 codes or a base 455 can be installed in a visually correct Gran Sport. · 1973 Buick Century Gran Sport Stage 1 455

Confidence

documented · 1973 Buick Century Gran Sport Stage 1 455

Correct value

XS for the 1973 Century GS 455 Stage 1 · 1973 Buick Century Gran Sport Stage 1 455

Where to check

engine production-code stamp; reconcile with casting dates and VIN derivative · 1973 Buick Century Gran Sport Stage 1 455