Reading the Casting Numbers on Your Holley Carburetor

The casting number stamped into your Holley carburetor is the most reliable way to identify it. This number tells you the model, when it was made, and often what engine it was designed for. The casting number is usually found on the main body of the carburetor — most often on the driver's side of the base plate or on the bowl itself.

Holley casting numbers follow a pattern: they typically begin with a four-digit number (like 4150, 4160, or 4500), followed by letters and additional numbers. The first four digits identify the carburetor family and its basic design. The letters and numbers that follow narrow down the specific year, process, and any special features.

You may also see a date code stamped nearby, usually in the format of a letter and number (like "A7" for January 1967, or "L2" for December 1962). This date code helps confirm when the carburetor was manufactured, though it is not always present on older models.

Key Takeaways

  • The casting number is stamped directly on the carburetor body, most commonly on the base plate or bowl, and is your primary identification tool.
  • The first four digits of the casting number identify the carburetor family — 4150 and 4160 are the most common street and performance models.
  • Letters and numbers following the main casting number indicate the year, engine process, and specific tuning for that model.
  • A date code (letter plus number) may appear separately and shows the month and year of manufacture.
  • Cross-referencing your casting number with a Holley parts manual or online database will give you the exact specifications and rebuild kit you need.

The Four-Digit Model Prefix and What It Means

The first four digits of your casting number define the carburetor's core design and intended use. 4150 and 4160 are the two most common prefixes you will encounter. The 4150 is a two-barrel carburetor designed for street engines and light performance work. The 4160 is also a two-barrel but was engineered for higher-flow applications and is often found on bigger-displacement engines.

4500 carburetors are four-barrel models, larger and more complex than the 4150 or 4160. These were used on full-size cars and trucks, as well as high-performance engines. 4300 is another four-barrel variant, typically found on older muscle cars and performance builds.

Less common prefixes include 2300 (a single-barrel model), 5200 (a two-barrel with different internals), and 6500 (a specialty model). If your casting number begins with something other than 4150, 4160, or 4500, note it down — it will help narrow your search when you consult a parts reference.

Decoding the Letters and Numbers After the Main Casting Number

After the four-digit prefix, you will see a series of letters and numbers. These suffixes tell you the specific year, engine displacement, and tuning specifications. For example, a casting number might read "4150-1" or "4160-H" — the letter or number at the end indicates a specific revision or year.

Holley did not use a completely standardized suffix system across all years, so the meaning of a particular letter or number can vary depending on the decade. A "C" suffix on a 1960s carburetor means something different than a "C" suffix on a 1980s model. This is why cross-referencing with a Holley service manual or a carburetor-specific database is important — it removes the guesswork.

Some carburetors also have a second line of numbers or letters stamped below the main casting number. This secondary stamp often indicates the specific tuning (jet sizes, needle position, float level) or a special process code. Write down everything you see stamped on the carburetor, even if some of it seems unclear.

Using Date Codes to Confirm Year of Manufacture

If your Holley has a date code, it appears as a single letter followed by a single digit. The letter represents the month (A for January, B for February, and so on through L for December), and the digit represents the year within a decade. For instance, "C5" means March 1965, and "L2" means December 1962.

Date codes are most reliable on carburetors made from the 1960s through the 1980s. Earlier models rarely have them, and some aftermarket or remanufactured carburetors may have been restamped or lack a date code altogether. If you find a date code, it should align roughly with the casting number's year — if they are far apart, the carburetor may have been rebuilt or the casting may be older than the actual assembly.

Where to Find the Casting Number on Your Carburetor

The location of the casting number varies slightly depending on the model, but it is always stamped directly into the metal body. On most 4150 and 4160 carburetors, look on the driver's side of the base plate (the flat part that bolts to the intake manifold). On 4500 four-barrel models, the casting number is often on the main body casting itself, sometimes on the passenger side.

If the carburetor is still mounted on the engine, you may need to remove it to see the casting number clearly. Use a flashlight and look carefully — the stamping can be shallow and hard to read if dirt or corrosion has built up. If the number is faint, try rubbing the area gently with a wire brush or fine steel wool to reveal it.

Write down the entire casting number exactly as it appears, including any date codes or secondary stamps. Take a photo if you can — this gives you a record to reference when you are looking up specifications or ordering parts.

Cross-Referencing Your Casting Number with Holley Resources

Once you have the casting number, the next step is to look it up in a Holley identification guide or parts manual. Holley publishes official service manuals that list casting numbers alongside specifications like float level, jet sizes, needle type, and the engine applications each carburetor was designed for. These manuals are available from Holley directly, through automotive parts suppliers, and sometimes as free PDFs online.

Online carburetor forums and enthusiast communities also maintain databases of casting numbers and their specifications. Websites dedicated to classic cars, muscle cars, or specific engine platforms often have Holley identification charts compiled by experienced builders. When using online sources, cross-check the information against at least one other source — user-submitted data can sometimes contain errors.

If you are rebuilding the carburetor, the casting number tells you which rebuild kit to order. Holley rebuild kits are matched to specific casting numbers because internal dimensions and component sizes vary between models. Ordering the wrong kit can result in poor performance or a carburetor that does not seal properly.

Common Holley Models and Their Typical Applications

The 4150 is the most popular Holley for street rods, classic cars, and mild performance engines. It flows around 600 cubic feet per minute (CFM) and is straightforward to tune and maintain. You will find 4150s on everything from 1950s hot rods to modern engine swaps.

The 4160 is a step up in flow capacity and is often chosen for engines with larger displacements or higher RPM ranges. It shares the same bolt pattern and basic layout as the 4150, so swapping between them is straightforward if you later want more flow.

The 4500 four-barrel is larger and more complex, with separate primary and secondary barrels. It was the factory choice for full-size American cars and trucks, and it remains popular for big-block engines and high-performance builds. Four-barrel carburetors require more tuning knowledge but offer better part-throttle response and fuel economy than a single four-barrel of equivalent size.

Frequently Asked Questions

What if the casting number is worn off or illegible?

If the stamping is too faint to read, try rubbing the area with fine steel wool or a brass brush to remove corrosion. If that does not work, you can sometimes identify the carburetor by its physical characteristics — bolt pattern, bowl shape, and internal components — but this is less reliable. A carburetor shop or experienced rebuilder may be able to identify it by sight.

Can I use a casting number from one carburetor to identify a different one?

No. Each casting number is specific to that carburetor's design and specifications. Using the wrong casting number to order parts or rebuild kits will result in incorrect components. Always identify your own carburetor directly.

Does the casting number tell me the CFM rating?

Not directly. The first four digits (like 4150 or 4160) indicate the general family and approximate flow range, but the exact CFM depends on the specific tuning and year. You will need to consult a Holley manual or parts database to find the precise CFM rating for your casting number.

What is the difference between a casting number and a part number?

The casting number is stamped into the metal during manufacturing and identifies the original design and year. A part number is assigned by Holley for ordering and inventory purposes and may be different. When ordering rebuild kits or replacement parts, use the casting number — it is more accurate than a part number alone.

Can I identify a Holley carburetor by its appearance alone?

You can make an educated guess based on size and shape — a small two-barrel looks different from a large four-barrel — but appearance alone is not reliable. Two different casting numbers can look nearly identical externally. Always locate and record the casting number for accurate identification.