Looking to crack the code on your GM engine’s serial number? Whether you’re breathing new life into a classic muscle car, confirming authenticity, or in search of the right specs for repairs, understanding how to interpret and look up GM engine serial numbers is invaluable. These codes reveal crucial details—like model year, displacement, and manufacturing plant—making them essential for identification and restoration.
This guide will show you how to find, decode, and reference GM (General Motors) engine serial numbers for brands like Chevy, Pontiac, Buick, Oldsmobile, Cadillac, and the LS engine series. Knowing these codes is particularly handy for classic car fans and restoration pros—especially when you need to match or verify your engine block.
GM has produced hundreds of different engines over the decades—such as the legendary Chevy 283 and the powerful 400 small-block. In this article, we’ll zoom in on some of the most popular GM engines and demystify the serial number lookup process. If you specifically own a Chevrolet engine, don’t miss our dedicated in-depth guide to Chevy engine serial number lookups.
What Is An Engine Serial Number?
The GM engine serial number—sometimes called the production code—uniquely identifies your engine. It contains valuable information, including the engine’s specifications, year, and original assembly location. Some codes also reference which model the engine was originally intended for. Essentially, it’s an engine’s fingerprint.
You’ll usually find the serial number on the engine block or cylinder head, but the exact placement (and the number of digits and letters) changes depending on engine type and manufacturing era. Older engines often have easy-to-read codes with straightforward information, while newer engines may require access to a specialized database for full decoding.
GM spans several brands and countless engine variants, so we can’t cover every code. Our focus here is on four popular types: Chevy inline-six, Buick “Fireball” V8, Pontiac V8, and the GM LS engine family. We’ve also included more engines and will keep expanding this guide.
Below, you’ll find an easy reference “cheat sheet” for quick lookups. And if you want a deeper understanding, keep reading—we’ll cover how to decode each character and number in the serial number on many major GM engines.
GM Engine Serial Number Lookup Cheat Sheet
| Engine Family | Displacement (L / CI) | Production Years | Serial Number Location |
|---|---|---|---|
| Chevy Inline-Six | 3.9L – 4.8L / 235 – 292 CI | 1929–1990 | Passenger side, near distributor or starter |
| Pontiac V8 | 4.9L – 7.5L / 301 – 455 CI | 1955–1981 | Front of block, below cylinder head |
| Buick “Fireball” V8 | 4.3L – 6.6L / 264 – 401 CI | 1953–1966 | Front of block, near intake manifold |
| GM LS Engine | 4.8L – 7.0L / 293 – 427 CI | 1997–Present | Rear driver-side, near transmission |
| Chevy Small-Block V8 (SBC) | 4.3L – 6.6L / 262 – 400 CI | 1955–2003 | Front passenger-side, below cylinder head |
| Chevy Big-Block V8 (BBC) | 6.5L – 9.4L / 396 – 572 CI | 1958–Present | Front passenger-side, below alternator |
| Chevy 90° V6 | 2.8L – 4.3L / 173 – 262 CI | 1978–Present | Rear driver-side, near transmission |
| Northstar V8 | 4.0L – 4.6L / 244 – 279 CI | 1993–2011 | Rear of block, near bellhousing |
| Oldsmobile Rocket V8 | 4.9L – 7.5L / 303 – 455 CI | 1949–1990 | Front of block, near water pump |
| Oldsmobile Diesel V8 | 5.7L – 6.2L / 350 – 379 CI | 1978–1985 | Rear driver-side, near transmission |
| Buick V6 | 3.0L – 4.1L / 181 – 252 CI | 1962–2008 | Front of block, near timing cover |
| Cadillac HT4100 | 4.1L / 249 CI | 1982–1987 | Rear of block, near intake manifold |
| Quad 4 | 2.3L – 2.4L / 138 – 146 CI | 1987–2002 | Side of block, near starter |
| Ecotec Engine Family | 1.4L – 2.5L / 85 – 151 CI | 2000–Present | Side of block, near oil filter |
| LT Engine Series | 5.3L – 6.2L / 325 – 376 CI | 2014–Present | Rear driver-side, near transmission |
| Duramax Diesel | 2.5L – 6.6L / 153 – 403 CI | 2001–Present | Passenger-side, near starter |
| Atlas I6 | 4.2L / 256 CI | 2002–2012 | Driver-side, near oil pan |
1. Chevy Inline-Six
Chevy’s inline-six engines feature a serial number with two main parts: the prefix (six-digit unit number, plant code, and year) and a suffix (one or two letters identifying the vehicle application).
The unit number begins at ‘1001’ at each plant and is used mainly for production tracking. Plants are usually coded as ‘F’ for Flint, Michigan, or ‘T’ for Tonawanda, New York.
For practical purposes, focus on the model year (so you know when it was built) and the suffix letter(s) (to determine the original application and specs).
GM Engine Serial Number Lookup & Decoding – Example (Chevy I6)
Let’s break down 0001001 F 54 YG:
- 0001001: Manufacturer’s sequential number
- F: Flint, Michigan assembly plant
- 54: 1954 model year
- YG: Indicates a 235ci inline-six for a 1954 Corvette with Powerglide
Suffixes have changed over the years—for instance, in 1957, Corvette engines might be identified with A, AD, or B (each corresponding to a different transmission or clutch setup).
Once you have your inline-six’s code, check the Old Car Manual Project database for details. This site offers comprehensive code listings maintained by fellow Chevy enthusiasts.
GM Engine Serial Number Lookup & Decoding – Chevy Inline-Six (2nd Gen)
Later Chevy inline-sixes have a format resembling their small- and big-block V8 relatives. The code’s prefix consists of the plant code and production date, while the suffix (two letters) signifies engine application.
Example: F1012 LH
- F: Flint, Michigan
- 1012: October 12 (production date)
- LH: 1967 230ci base engine for an automatic-equipped car with smog pump and A/C
Suffix codes change year to year. “LH” is specific to a 1967 model, while “BH” is the equivalent for 1968. Once you gather your number, check the Camaro Research Group registry for clarification.
2. Pontiac V8
Unlike Chevy, Pontiac V8 engine numbers can contain a date code, casting number, and application (engine usage) code—with codes that may overlap through the years.
You’ll generally spot the date code and casting number at the back of the block (under the distributor), and the application code at the front passenger side. The casting number is for GM’s records, but you can decode the date/application codes.
The date code is a letter plus three numbers. The application code is usually two letters (sometimes letters and numbers), which tells you engine displacement and intended use.
GM Engine Serial Number Lookup & Decoding – Pontiac V8
Example: A249 XE
- A: January (month code; A to L, one letter per month—except in 1967, when December was “M”)
- 24: Day of the month
- 9: Final digit of production year; needs cross-referencing (could be ’59, ’69, or ’79, depending on suffix/application)
- XE: Suffix denoting a 1969 428ci engine
Always cross-reference application and date codes to verify the year and specifications since similar number sets can apply to different decades. Look up your code on the Pontiac Power database for full details.
3. Buick “Fireball” V8
The Buick “Fireball” V8 line has several generations and placement of the serial number depends on the exact engine and production year:
- 1953–56 (264/322): On top of driver’s side cylinder bank, above exhaust manifold
- 1957–66 (364/401/425): Passenger side block front, ahead of valley pan
- 1961–63 (215): Passenger side, front of cylinder head
- 1964–66 (340): Driver’s side, crankcase front face (serial); passenger side, crankcase (production code)
- 350, 400, 430: Production code between forward right exhaust manifold branches; serial number between rear branches
- 455: Production code near left-side exhaust manifold; serial under deck
GM Engine Serial Number Lookup & Decoding – Buick “Fireball” V8
The serial is typically eight digits (part of the VIN); the production code is five digits, with the first two being letters or alphanumeric (for size and production date). There’s less public info for Buick decoding than for Chevy or Pontiac, but first two production code digits are usually enough to ID engine variant.
Once found, check the TeamBuick database for reference codes and further insight.
4. GM LS Engine
If your GM vehicle came with an LS engine from the factory, you can often identify it via the 8th digit of the VIN. However, the same letter can reference more than one engine (for example, “G” might mean a 5.7L LS1 or a 6.0L L96, depending on the vehicle).
Trucks and passenger cars often share codes, so cross-reference with your model and year via resources like Summit Racing’s guide. For detailed parts matching, the VIN is often all you need.
If you’re dealing with a stand-alone engine (such as one from a scrapyard), you’ll need the block’s 8-digit casting number (found near the rear, passenger side) or the cylinder head code. The casting number tells you which LS block you have—but not necessarily year or application, so you’ll need to search online or by reference books.
For engine production date, remove the cylinder heads: there’s a four-digit alphanumeric code on the rear driver’s side of the block. For example, C246 breaks down as C=March, 24=day, 6=2006.
Cylinder heads on LS engines are often interchanged. Head casting numbers (like LS7’s “452”) further refine your identification. For an overview of all possible numbers, check MotorTrend’s complete cylinder head chart.
5. Chevy Small-Block V8 (SBC)
SBC engine serial numbers are stamped on a flat pad at the front passenger side of the block.
The number starts with the assembly date (a letter for the month, followed by day and year), followed by a suffix code revealing engine configuration.
Let’s look at V0403HR:
- V: Flint plant
- 0403: April 3rd assembly
- HR: 1958 283ci V8 (185hp)
GM Engine Serial Number Lookup & Decoding – Chevy Small-Block V8 (SBC)
For example, FA means a 1957 265ci V8 (162hp), and GD stands for a 1962 283ci (170hp).
Use resources such as NastyZ28.com or outintheshop.com for complete lists of suffixes and detailed decoding.
GM used this format for decades, making SBC decoding familiar even for later versions.
6. Chevy Big-Block V8 (BBC)
Find the BBC serial number stamped on a pad at the front, passenger side, below the head.
The number begins with the assembly date (month letter + day), then a suffix code. T0105IV means Tonawanda plant, January 5 assembly, and the IV suffix identifies it as a 1972 402ci V8 (240hp) for a Chevelle with Turbo-Hydramatic.
- JE: 1969 427ci, 430hp (Corvette)
- CRX: 1965 396ci, 375hp (Impala)
See earlier-linked decoding resources for the full register of suffixes and specs.
7. Chevy 90° V6
Look for the serial on a front passenger-side pad by the water pump. The sequence is the same as the V8s: month letter, day, year, and then a multi-character suffix for engine details.
For F0723ZDR:
- F: Flint assembly
- 0723: July 23rd
- ZDR: Late 80s 4.3L V6 with TBI, passenger car
Common suffixes: ZDA (early 80s 229ci/2-barrel), ZDM (mid-80s 4.3L TBI, truck). Use previous database links for detailed decoding.
8. Northstar V8
The Northstar’s code sits at the rear of the block by the bellhousing. The serial usually starts with a plant identifier, followed by the year and day number.
- Y: Orion Plant, Michigan
- 299: 299th day of year
- 0154: Sequence that day
Suffixes add insight: 9Y (4.6L, 275hp), 9S (4.6L, 300hp). Cross-reference earlier databases for model specifics.
9. Oldsmobile Rocket V8
On the Rocket V8, look at the left side of the block above the oil pan rail.
Decoding looks like: 57K100001 = 1957 (year), Lansing, Michigan (“K”), then a unique production sequence.
Suffixes such as D88 (late 50s high-compression 371ci) or E80 (394ci high-performance) can further narrow down the engine’s specifics.
Use provided links for full decoding.
10. Oldsmobile Diesel V8
The Olds Diesel V8 code is stamped at the driver’s front, near the head. The format (82L123456) means: 1982, Lansing, MI (“L”), then sequence number. Suffix LF9 (5.7L diesel) often appears on the most common models.
Check previous links for details.
11. Buick V6
Find the code on the driver’s block, just behind the head or at the transmission interface. A typical code (79B567890) decodes as 1979, Flint (“B”), and sequence. Suffix LD5 = 3.8L naturally aspirated, LC2 = turbo 3.8L (Grand National).
Reference earlier links for comprehensive decoding.
12. Cadillac HT4100
To decode a HT4100, find the code at the driver’s side front block. Reading 83C234567 gives 1983, Detroit plant (“C”), and unique sequence. Suffix “8” confirms it’s an HT4100 model.
Cross-reference using GM/Cadillac registries for extra precision.
13. Quad 4
Quad 4 serial numbers are cast at the rear of the block, exhaust side. Example: 90A123456 = 1990, Lansing (“A”), and sequence. Suffix LGO marks the 2.3L high-output DOHC.
Consult earlier links for full suffix dictionaries.
14. Ecotec Engine Family
On Ecotec engines, find the code near the exhaust manifold on the block. 04L789012 tells you: 2004, Spring Hill (“L”), sequence number, with suffix LE5 meaning 2.4L DOHC. Earlier databases will decode further.
15. LT Engine Series
Locate LT engine numbers at the front block, above the passenger-side oil pan. Example: 18K654321 = 2018, Bowling Green (“K”), manufacturing sequence. LT1 means 6.2L V8.
Full breakdowns are available in the linked databases.
16. Duramax Diesel
Duramax serials are on the driver’s block, lower middle. Example: G0928-123456 is Moraine, Ohio (“G”), September 28, and sequence. Suffix LML designates the 6.6L V8 turbo diesel.
Earlier links will help with detailed decoding.
17. Atlas I6
Atlas I6 codes are stamped mid-driver’s side block. J0310-678910 = Moraine, Ohio (“J”), March 10, then sequence. Suffix LL8 identifies the 4.2L inline-six.
Online decoding resources (listed earlier) will help clarify individual codes.
