What size is the intake valve on a Chevy 350?

The intake valve size for a typical Chevy 350 small-block is 1.94 inches in diameter.

In this article we break down what that means for stock engines, variations you may encounter with aftermarket heads, and how to confirm the exact valve size on your specific build.

Typical stock size

Across most factory 350 small-blocks, the intake valve diameter measures 1.94 inches (49.3 mm). Some aftermarket or performance heads may use a larger valve, commonly 2.02 inches (51.3 mm), to improve airflow. The exhaust valve is typically smaller at about 1.50 inches (38.1 mm).

• Stock factory small-block 350 heads: intake valve ≈ 1.94 inches (49.3 mm).


• Common aftermarket/high-flow heads: intake valve ≈ 2.02 inches (51.3 mm).

Knowing the valve size helps ensure proper piston-to-valve clearance, spring compatibility, and overall breathing in a build.

How to verify your exact valve size

To confirm the intake valve size for your particular Chevy 350, identify the cylinder head casting number and consult the manufacturer’s specs or reputable references. If the casting number isn’t available, you can measure the valve diameter directly.

1. Locate the head casting number, typically on the outside of the cylinder head near the exhaust port or rocker arm area.


2. Look up the casting number in GM head catalogs or the head supplier’s data to verify the intake valve diameter for that head.


3. If you cannot identify the head, remove a valve or obtain the head to measure the valve face diameter with calipers. Most measurements will reveal 1.94" or 2.02" for common SBC heads.


4. Cross-check the intake valve size with your cam, springs, and compression setup to ensure compatibility and prevent interference.

In practice, most builders rely on the head casting data rather than guessing, because the valve size drives spring choice and clearance in both stock and performance builds.

Related considerations

Note that head design and generation can affect other related measurements, such as the valve stem diameter, valve seat width, and overall port size. For example, the Chevy 350's exhaust valve diameter is typically 1.50 inches, but aftermarket heads vary as well.

Summary

In short, the standard intake valve diameter for a Chevy 350 small-block is 1.94 inches. Larger 2.02-inch intakes appear on some aftermarket or high-flow heads. Always verify your exact valve size by checking the head casting number or measuring directly before ordering parts or starting a build.

What size intake valve is a 305 Chevy?

1.84″ x 1.50″
Let's take a look at the Chevy 305 heads as a good example: The normal valve size in the “performance” 305 head is 1.84″ x 1.50″. Thinking that “bigger is better” many people install 1.94″ intake valves in 305 heads.

Are intake and exhaust valves the same size?

No, intake and exhaust valves are not the same size; intake valves are generally larger than exhaust valves. This size difference allows more air-fuel mixture into the combustion chamber for maximum power, while the smaller exhaust valve handles the smaller volume of spent exhaust gases, which are also much hotter. 

• Intake valve: It is larger to maximize the flow of air and fuel into the cylinder during the intake stroke. 
• Exhaust valve: It is smaller because the volume of exhaust gases is less than the incoming air-fuel mixture, and the gases are significantly hotter. A smaller exhaust valve helps manage the high heat to prevent issues like pre-ignition in the next cycle. 

What size is the main journal on a 350 Chevy?

The main journal size for a standard 350 sbc is 2.45 inches (2.449 inches), which is considered the "large" main journal size for the small-block Chevrolet engine family. This is the same size as the rod journals on a 400 sbc and differs from the smaller journal sizes found in earlier 283 and 302 engines. 

• Main Journal Diameter: 2.45 inches (2.449 inches)
• Rod Journal Diameter: 2.100 inches

How do I know the size of the valve?

Valve sizing ensures a valve operates efficiently and reliably by matching its flow capacity to the system's requirements through calculations and rules of thumb. Key factors include the required flow rate, pressure drop, and fluid characteristics. For simple applications, match the valve size to the pipe size; for more complex control valve sizing>>, calculate the valve coefficient (Cvcap C sub v𝐶𝑣) to determine the correct size, and ensure the valve will operate within the ideal 20-80% open range at maximum flow.
 
This video explains the basics of control valve sizing: 1mFisher Valves & InstrumentsYouTube · Feb 11, 2019
Simple applications

• Match the pipe size: For non-control valves, the general rule is to match the valve size to the pipe size it is connecting to. For example, use a 1-inch valve on a 1-inch pipe. 
• Use reducers if needed: If a valve is only available in a standard size, you can use fittings to connect it to a smaller pipe. 

Control valve sizing

• Calculate the valve coefficient (Cvcap C sub v𝐶𝑣): This is a key step in control valve sizing. You will need to know the flow rate (Qcap Q𝑄), the pressure drop (ΔPcap delta cap PΔ𝑃) across the valve, and the specific gravity of the fluid (Gcap G𝐺). 
• Use the Cvcap C sub v𝐶𝑣 formula: A common equation for liquids is Q=CvΔPGcap Q equals cap C sub v the square root of the fraction with numerator cap delta cap P and denominator cap G end-fraction end-root𝑄=𝐶𝑣Δ𝑃𝐺, where Qcap Q𝑄 is the flow rate in gallons per minute, ΔPcap delta cap PΔ𝑃 is the pressure drop in psi, and Gcap G𝐺 is the specific gravity. 
• Refer to manufacturer charts: Once you calculate the required Cvcap C sub v𝐶𝑣 value, use the manufacturer's charts to find the valve size that provides that coefficient. 
• Use a rule of thumb: A common guideline for control valves is to size them one or two sizes smaller than the pipe, but this should be used as an indicative guide only. For example, a 3" valve might be used in a 4" pipe. 

This video explains how to calculate the valve coefficient: 48sCalibration AcademyYouTube · May 15, 2023
Operating range and other factors

• Control range: The valve should ideally be able to operate between 20% and 80% open at the maximum required flow rate to ensure good control. 
• Pressure drop: The pressure drop across the valve should be a significant portion of the total system pressure drop, typically 50-60% of the frictional pressure loss in the piping system. 
• Fluid properties: The specific gravity of the fluid is critical, as it affects the flow rate. You may also need to consider factors like viscosity and temperature. 
• Turndown ratio: The ratio of maximum to minimum flow rates (turndown) should be limited to a reasonable range, such as 5:1 or 10:1 depending on the valve trim.