How to find your Holley carb model number

Your Holley carburetor has a model number stamped or cast into the body itself — you do not need to remove it or take it apart. The number is usually a four or five-digit code, and it tells you exactly which Holley model you own and when it was made.

The most common location is on the passenger side of the main body, just below where the air cleaner bolts on. Look for a raised or recessed stamp. On some models, especially older ones, the number may be on the driver's side instead, or cast into the base plate underneath. If you cannot find it on the body itself, check the fuel inlet fitting — some Holleys have a date code stamped there.

Write down exactly what you see, including any letters. A number like 4150 or 4160 tells you the family; a number like 4150-1 or 4150-2 tells you the specific variant. Take a photo if the stamp is hard to read — you may need to show it to a parts supplier or mechanic later.

Key Takeaways

  • The model number is stamped or cast into the carburetor body, usually on the passenger side below the air cleaner mounting point.
  • A four or five-digit code like 4150 or 4160 identifies the carburetor family and tells you its basic design and fuel delivery system.
  • The suffix number after the dash (like 4150-1 or 4150-2) identifies the specific variant, which matters for finding the right rebuild kit or replacement parts.
  • If you cannot find the number on the body, check the fuel inlet fitting or the base plate, and take a photo of the stamp for reference.

Understanding Holley model numbers and what they mean

Holley carburetors use a numbering system where the first digits tell you the carburetor's size and type. The 4150 and 4160 are the most common models you will encounter — both are four-barrel carburetors, meaning they have four fuel delivery circuits. The 4150 is a vacuum-secondary design, where the secondary barrels open gradually as engine load increases. The 4160 is a mechanical-secondary design, where the secondaries open based on throttle position.

Other common Holley models include the 2300 (a two-barrel carburetor), the 4500 (a larger four-barrel for high-performance engines), and the 6500 (an even larger model for racing). The number itself does not tell you the year the carburetor was made — only the design family. A 4150 made in 1975 and a 4150 made in 1995 have the same basic number but may have different internal parts.

The suffix number matters more for finding parts. A 4150-1 and a 4150-2 are both 4150s, but they have different internal specifications — different jets, metering rods, or secondary spring rates. When you order a rebuild kit or replacement gasket set, you need the full number including the suffix.

Where to look if the number is worn or missing

If the main stamp is too worn to read, look for a date code instead. Holley often stamped a date code on the fuel inlet fitting or on the base plate. The date code is usually two or three characters — a letter for the month and a number for the year. For example, "A5" might mean January 1975. This does not tell you the exact model, but it narrows down the year and helps you cross-reference with a parts catalog.

If you have the carburetor off the engine, you can also look at the bowl casting — the large chamber that holds fuel. Some Holleys have a partial model number or date code cast into the bowl itself. You may also find a part number on the fuel bowl cover or on internal components like the metering block, though these are harder to read without disassembly.

If you still cannot identify the model, take a clear photo of the entire carburetor from multiple angles and bring it to a Holley dealer or a carburetor specialist. They can often identify it by shape and internal design even if the stamp is gone.

How to tell the difference between vacuum and mechanical secondaries

If you have found the model number but want to understand what type of carburetor you own, look at the secondary side of the carburetor — the half of the four-barrel that handles higher engine speeds. On a vacuum-secondary carb like the 4150, the secondary barrels are held closed by a spring and opened by engine vacuum. You will see a vacuum diaphragm mounted on the side or back of the carburetor — a cylindrical or rectangular chamber with a hose running to the engine.

On a mechanical-secondary carb like the 4160, there is no vacuum diaphragm. Instead, the secondary barrels are linked directly to the throttle linkage. When you press the gas pedal, the throttle cable opens the primary barrels first, and as you press further, a mechanical rod or lever opens the secondary barrels. This design is simpler and more direct, which is why it is common on performance engines.

Vacuum-secondary carbs are smoother for street driving because they open the secondaries gradually as the engine needs more fuel. Mechanical-secondary carbs respond faster to throttle input, which is why they are preferred for racing or high-performance applications. Knowing which type you have helps you understand how your carburetor behaves and what parts you will need if it needs repair.

Reading the casting date and production year

Even if you have the model number, you may want to know what year the carburetor was actually made. Holley cast a date code into most carburetors, usually on the fuel bowl or on the main body near the model number. The code is typically a single letter (representing the month) followed by a number (representing the year).

The letter codes run A through L for January through December. The year code varies — some Holleys use the last digit of the year (so 5 = 1975 or 1985), while others use a two-digit year code. A carburetor marked "C7" could mean March 1977 or March 1987, depending on the era. Cross-referencing the model number with a Holley parts catalog or a carburetor identification guide will help you pin down the exact year.

The production year matters if you are restoring a classic car and want original parts, or if you are trying to understand how old the carburetor is and whether it is likely to have worn internal components. A carburetor from the 1970s may have different fuel delivery characteristics than one from the 1990s, even if they share the same model number.

Common Holley models and their basic uses

The 4150 and 4160 are the workhorses of the Holley line. The 4150 (vacuum-secondary) is the most common choice for street cars and mild performance builds because it delivers smooth power without sudden surges. The 4160 (mechanical-secondary) is preferred for racing, drag racing, and high-horsepower engines because it responds when ready to throttle input.

The 2300 is a two-barrel carburetor, smaller and simpler than the four-barrels. It is common on older trucks, economy cars, and light-duty engines. If you have a 2300, you will see only two fuel delivery circuits instead of four.

The 4500 is a larger four-barrel designed for big-block engines and high-performance applications. It flows more fuel than a 4150 or 4160 and is often seen on muscle cars and racing engines. The 6500 is even larger and is typically used only in racing or extreme performance builds.

If your model number does not match any of these, you may have a specialty model like a 3310 (a three-barrel), a 5200 (a two-barrel performance carb), or a marine or industrial variant. A Holley parts catalog or identification guide will help you narrow it down.

What to do once you have identified your carburetor

Once you know your model number and suffix, you can order the correct rebuild kit or gasket set if your carburetor needs service. A rebuild kit includes all the internal seals, gaskets, and wear parts needed to restore the carburetor to working condition. You will need the full model number (including the suffix) to order the right kit — ordering the wrong one can mean parts that do not fit or a carburetor that does not run correctly.

You can also use the model number to find tuning specifications — the correct jet sizes, needle positions, and air-fuel mixture settings for your engine. These specifications vary by model and year, so having the exact number is important if you are tuning the carburetor or troubleshooting a running problem.

If you are buying a used Holley or trying to determine if a carburetor will fit your engine, the model number tells you whether it is the right size and type. A 4150 will not bolt onto an engine designed for a 2300, and a 4160 may not work well on an engine that needs a vacuum-secondary design. Knowing what you have helps you make the right choice.

Frequently Asked Questions

What if the model number has letters in it, not just numbers?

Letters in the model number are normal and important. For example, a 4150H or 4160P tells you the carburetor has specific features or was made for a particular process. The letter is part of the full model designation and must be included when ordering parts or looking up specifications. Write it down exactly as it appears.

Can I use a carburetor with a different suffix number on my engine?

It depends on the difference between the suffixes. A 4150-1 and a 4150-2 are similar enough that they may work, but they have different internal tuning. If you swap them, the engine may run lean or rich, and fuel economy or performance may suffer. For the best results, use the exact model your engine was designed for or consult a carburetor specialist.

Where is the model number on a Holley that has been painted or powder-coated?

If the carburetor has been painted, the stamp may be hidden under the paint. Carefully scrape a small area with a plastic scraper or soft brush to reveal the number underneath. Do not use a wire brush or sandpaper, as these can damage the casting. If the paint is thick, you may need to remove it from that area to read the number clearly.

Does the model number tell me what year my car was made?

No. The carburetor model number tells you the design family, not the year of manufacture. A 4150 could have been made in 1970 or 2010. To find the production year, look for the date code (usually a letter and number) cast into the bowl or body. That code tells you when the carburetor was actually built, which may be different from when the car was assembled.

What if I cannot find any number or code on my carburetor at all?

This is rare but can happen if the carburetor has been heavily modified, repaired, or if the casting is too worn. In that case, take photos of the carburetor from all angles and bring them to a Holley dealer or carburetor specialist. They can often identify it by its shape, size, and internal design. You can also check if there is a part number on any internal components by carefully disassembling the air horn (the top cover).