DOHC vs SOHC vs OHV: Which Engine Valve Train is Best?

When it comes to internal combustion engines, there are many factors that contribute to their performance. One of these factors is the valve train, which is the system responsible for opening and closing the valves that allow air and fuel into the cylinders and exhaust gases out. There are three main types of valve trains: DOHC, SOHC, and OHV. Each type has its own advantages and disadvantages, and the best choice for a particular engine depends on the desired performance characteristics.

Understanding Valve Trains

Before diving into the differences between DOHC, SOHC, and OHV, it's important to understand the basics of how valve trains work. The valve train consists of several components, including:

• Camshaft: A rotating shaft with lobes that open and close the valves.
• Valves: Mechanical components that open and close the intake and exhaust ports.
• Valve Springs: Springs that keep the valves closed when they are not being opened by the camshaft.
• Rocker Arms: Levers that transfer the motion from the camshaft to the valves.
• Pushrods: Rods that connect the camshaft to the rocker arms in some valve train designs.

The camshaft is driven by the crankshaft, which is the main rotating shaft in the engine. As the crankshaft rotates, the camshaft also rotates, and the lobes on the camshaft push on the rocker arms, which in turn open and close the valves.

DOHC (Double Overhead Camshaft)

A DOHC engine has two camshafts, one for each bank of cylinders. Each camshaft controls the intake and exhaust valves for its respective bank of cylinders. This configuration allows for more precise control over valve timing and lift, which can improve engine performance.

Advantages of DOHC:

• Higher Revving: DOHC engines can typically rev higher than SOHC or OHV engines because they have more precise valve control.
• Better Performance: The improved valve timing and lift of a DOHC engine can lead to increased horsepower and torque.
• More Efficient Breathing: The more precise valve control in a DOHC engine can lead to better airflow into and out of the cylinders, improving efficiency.

Disadvantages of DOHC:

• More Complex: DOHC engines are more complex than SOHC or OHV engines, which can make them more expensive to manufacture and maintain.
• Heavier: The extra camshaft in a DOHC engine adds weight to the engine, which can slightly reduce performance.

SOHC (Single Overhead Camshaft)

A SOHC engine has only one camshaft, which controls both the intake and exhaust valves for all cylinders. This configuration is simpler and less expensive than DOHC, but it can limit engine performance.

Advantages of SOHC:

• Simpler Design: SOHC engines are simpler to design and manufacture than DOHC engines.
• Lower Cost: The simpler design of a SOHC engine means it is typically less expensive to manufacture.
• Lighter Weight: SOHC engines are lighter than DOHC engines, which can improve performance.

Disadvantages of SOHC:

• Less Precise Valve Control: A single camshaft cannot control valve timing and lift as precisely as two camshafts.
• Lower Rev Limit: SOHC engines typically have a lower rev limit than DOHC engines.
• Reduced Performance: The less precise valve control in a SOHC engine can lead to reduced horsepower and torque.

OHV (Overhead Valve)

An OHV engine has the camshaft located in the engine block, below the cylinder heads. The camshaft is connected to the valves via pushrods and rocker arms. This configuration is the simplest and least expensive of the three types, but it also offers the least performance potential.

Advantages of OHV:

• Simplest Design: OHV engines are the simplest and least expensive to design and manufacture.
• Durable: The simpler design of an OHV engine makes it more durable and less prone to failure.

Disadvantages of OHV:

• Lower Performance: OHV engines have the lowest performance potential of the three types due to their less precise valve control.
• Reduced Fuel Efficiency: The less efficient valve control in an OHV engine can lead to reduced fuel efficiency.
• Lower Rev Limit: OHV engines typically have a lower rev limit than SOHC or DOHC engines.

Which Valve Train is Best?

The best type of valve train for a particular engine depends on the desired performance characteristics. DOHC engines offer the best performance potential, but they are also the most complex and expensive. SOHC engines offer a good balance of performance and affordability, while OHV engines are the simplest and least expensive but offer the least performance potential.

In general, DOHC engines are typically found in high-performance vehicles, while SOHC engines are more common in everyday vehicles. OHV engines are often used in older or less expensive vehicles.

Conclusion

Understanding the differences between DOHC, SOHC, and OHV valve trains is important for anyone interested in engines. Each type has its own advantages and disadvantages, and the best choice for a particular application depends on the desired performance characteristics and budget.