If you are about to order an engine, cooling, ignition or driveline part for a Holden, the single most useful thing you can do first is read the engine number off the block. It confirms the exact engine variant, which is what a parts supplier needs before quoting anything that bolts to the motor.
This guide explains the two numbers people call the “engine number”, where each Holden engine family stamps it, how the old prefix codes work, and what to send with a parts enquiry. For the full enquiry-ready reference, use the Holden engine number guide.
Quick answer
- The number that matters for parts is the stamped engine serial number, usually with a prefix that identifies the engine type.
- On Holden inline-sixes it is on a machined pad on the right-hand side of the block; on the 253/308 V8 it is on the left-hand side.
- Modern V6 and LS V8 engines use a GM engine code (Ecotec, Alloytec, LS1) plus a stamped serial — send both.
- Wipe the pad clean before reading it; air-conditioning compressors and brackets often hide it.
Two numbers, one of them matters most
On almost every Holden there are two things owners call the “engine number”:
- The stamped engine serial number. A unique number stamped into a machined pad on the block, usually carrying a prefix that identifies the engine type and state of tune. This is the number recorded on the compliance plate and registration papers, and it is the one that confirms the exact engine variant for parts.
- The cast engine identity. A raised casting mark (for example a “253” or “308” cast into a V8 block) or a cast date code. Useful to confirm the engine type, but it is not a unique serial.
For matching parts, send the stamped serial and its prefix. The casting marks help confirm you are reading the right engine.
Where the engine number is, by engine family
| Engine family | Where the number is stamped |
|---|---|
| Inline-six (grey, red, blue, black motors) | Machined pad on the right-hand side of the block (viewed from the rear), above the engine-mount boss. The pad often needs wiping clean to read. |
| 253 / 308 V8 (4.2L / 5.0L) | Machined pad above the engine mounting on the left-hand side of the block (viewed from the rear). On air-conditioned cars the compressor can obscure it. |
| Imported Chev V8 (307 / 327 / 350) | Front pad of the cylinder head, right-hand side. |
| V6 (Buick 3.8 / Ecotec / Alloytec) | Stamped on the front left-hand face of the block, below the ignition coil area. |
| Gen III / Gen IV LS V8 (LS1, LS2, L76, L77, L98, LS3) | Stamped on a machined pad; the vehicle build/engine plate is on the radiator support (VT–VZ) or passenger strut tower (VE/VF). |
Locations can vary slightly by year and accessory layout, so treat the table as a starting point. The Commodore engine number location guide covers the VE, VY and VZ in more detail.
How the prefix system works
Older Holden engines use a prefix that tells you the capacity and state of tune. On six-cylinder and early V8 engines the prefix is a number (capacity) plus a letter, for example 186S, 202X or 308H. After the HQ, Holden began using the second letter of the model code as the first letter of the prefix, which is why HQ–HJ V8s show prefixes such as QR (253) and QT (308).
Modern engines do not follow that logic. The Ecotec V6, Alloytec V6 and the LS-series V8s use GM RPO codes (LS1, LS2, L98 and so on) alongside a separate stamped serial. For these, the engine code plus the stamped number together identify the part you need. To tell the modern Commodore engines apart, see Ecotec vs Alloytec vs LS engine identification.
| Engine | Example prefixes |
|---|---|
| 186 red six | 186S, 186P (HR–HG, LC XU-1) |
| 202 red six | 202L, 202P, 202X (HQ on, LJ XU-1) |
| 253 V8 (4.2L) | 253H, QR, ZR |
| 308 V8 (5.0L) | 308H, QT, ZT, WT |
These prefix lists are most useful on older and enthusiast Holdens (Torana, Monaro, Kingswood-era and early Commodore) where numbers-matching originality matters.
What to send for a parts enquiry
- The full stamped engine number, including any letters in the prefix.
- The engine family or code if you know it (for example Ecotec, Alloytec, LS1).
- The car’s model, series and build year from the compliance plate.
- Your VIN — see the Holden VIN number guide for where to find it.
- What the part is, and which side or position it sits in.
When you have those details, send them through the Holden parts enquiry page and we will check availability.