Is a Double Overhead Cam (DOHC) Engine Good?

Yes—DOHC engines are generally a strong choice because they enable better airflow, higher power at high rpm, improved efficiency, and cleaner emissions, thanks to precise control of valve timing and lift. That said, they’re typically more complex, can be costlier to build and repair, and take up more space than simpler designs like SOHC or pushrod (OHV) engines. The best option depends on your priorities: performance and efficiency often favor DOHC; simplicity, packaging, and low-end torque can favor alternatives.

What DOHC Means and How It Works

“Double overhead cam” describes an engine with two camshafts mounted in the cylinder head—one operating intake valves and the other operating exhaust valves. Most modern DOHC engines use four valves per cylinder, which improves breathing and supports higher rpm power. DOHC layouts also make it easier to implement independent variable valve timing on both intake and exhaust cams, and in some cases variable valve lift, enabling fine-grained control over performance, fuel economy, and emissions across the rev range.

Key Advantages

The following points outline why DOHC designs remain the default in many modern passenger cars and motorcycles.

• Stronger high-rpm power: More valves and straighter ports enhance airflow, helping engines breathe better at speed.
• Precision valve control: Independent cam phasing (and, on some engines, variable lift) broadens the power band and optimizes efficiency.
• Efficiency and emissions: Better combustion control aids fuel economy and helps meet stringent emissions standards.
• Turbocharging synergy: DOHC heads handle boosted airflow effectively, supporting high specific output from downsized engines.
• Refinement: Modern DOHC valvetrains can be smooth and quiet, enhancing daily drivability.

Taken together, these advantages explain why DOHC technology dominates current car lineups, especially in vehicles that balance performance with efficiency.

Trade-offs and Drawbacks

Despite their strengths, DOHC engines are not a universal best fit. Consider these common downsides.

• Complexity and cost: More parts (two cams, additional hardware) can raise manufacturing and repair costs.
• Size and packaging: DOHC heads are typically taller and wider than pushrod designs, which can complicate engine bay packaging.
• Maintenance sensitivity: Timing belts or chains, guides, and cam phasers require proper oil and service; failures can be costly.
• Low-end torque tuning: While modern systems mitigate it, some DOHC setups historically favored top-end power over off-idle torque.
• Misattributed issues: Problems like intake valve carbon buildup stem from direct injection and PCV design, not from DOHC architecture itself.

These factors don’t negate DOHC’s benefits, but they do highlight why simpler alternatives still thrive in certain vehicles and use cases.

How It Compares to SOHC and Pushrod (OHV) Engines

SOHC vs. DOHC

Single overhead cam (SOHC) engines can be lighter and cheaper, and some designs still manage four valves per cylinder via rocker arms. However, SOHC typically offers less independent control of intake and exhaust timing and lift, limiting fine-tuning versus DOHC. For many budget-focused or compact applications, SOHC can be sufficient, but performance and emissions optimization often favor DOHC.

Pushrod (OHV) vs. DOHC

Pushrod engines place the cam in the block, using pushrods to actuate valves. They’re compact, robust, and known for strong low- to midrange torque—ideal for trucks and towing—and they package well in longitudinal layouts. However, they commonly use two valves per cylinder and can be more constrained at very high rpm. Modern OHV V8s (such as those from GM) still deliver excellent power, efficiency, and durability, showing that “best” depends on the mission, not just the cam layout.

When a DOHC Engine Makes the Most Sense

These scenarios illustrate where a DOHC design is likely to deliver clear benefits.

1. Performance cars that need strong high-rpm power and precise response across the rev range.
2. Turbocharged, downsized engines targeting high efficiency and stringent emissions standards.
3. Hybrids using Atkinson/Miller strategies that rely on sophisticated valve timing control.
4. Daily drivers seeking a blend of refinement, economy, and broad usability—common in modern compacts and crossovers.

If your priorities align with these scenarios, a DOHC engine is often the most compelling choice.

Ownership and Maintenance Tips

If you’re buying or maintaining a DOHC vehicle, the following practices help ensure reliability and longevity.

• Mind the timing system: Know whether you have a belt, chain, or “wet belt.” Belts often have replacement intervals; chains are designed for life but can suffer from worn guides or tensioners.
• Use the correct oil: Proper viscosity and timely changes are crucial for cam phasers and hydraulic lifters to operate correctly.
• Listen at startup: Rattles on cold start can hint at chain, guide, or phaser issues—address early to prevent bigger repairs.
• Valve lash checks: Some engines with mechanical lifters need periodic adjustment; many modern designs use hydraulic lifters that are maintenance-free.
• Keep PCV and software up to date: A healthy PCV system and current engine control software help prevent deposits and maintain VVT performance.

Staying ahead on these basics preserves the advantages DOHC engines are designed to deliver.

Common Misconceptions

DOHC often gets credit—or blame—for things that aren’t inherent to the design. Here are clarifications.

• “DOHC always has better torque”: Torque shape is largely about displacement, boost, and tuning—not just cam layout.
• “More cams mean unreliable”: Modern materials and oil control make DOHC very durable when maintained properly.
• “Carbon buildup is a DOHC problem”: It’s linked to direct injection and ventilation design; port injection or dual-injection strategies mitigate it.

Understanding what DOHC does—and doesn’t—do helps you judge the engine on its true merits.

Bottom Line

DOHC engines are generally “good” because they offer superior breathing, precise valve control, and a strong balance of power, efficiency, and emissions performance. The trade-offs are greater complexity, packaging demands, and potentially higher maintenance costs. For most modern cars, DOHC is the right fit; for heavy-duty towing, extreme simplicity, or certain packaging constraints, SOHC or OHV may be better.

Summary

In most contemporary vehicles, DOHC is a smart, future-facing choice that supports strong performance and efficiency. It’s not automatically best for every use case, but if you value broad power delivery, modern emissions compliance, and refinement, a DOHC engine is likely to serve you well.

Is a DOHC engine better for performance?

DOHC engines generally offer better performance and higher power output compared to SOHC engines. The separate camshafts allow for more precise valve timing and higher revving capabilities, resulting in increased power and torque delivery.

What are the disadvantages of DOHC?

DOHC engines also allow the spark plug to be placed right in the middle of the combustion chamber which in turn promotes efficient combustion. The disadvantage of such a setup is more weight, higher costs and also the fact that driving two camshafts requires more components.

What is the advantage of double overhead cam?

DOHC has two crankshafts and two camshafts which are above the cylinder block. This allows the engine to have more and more accurate opening valves, thereby increasing fuel combustion efficiency and engine performance.

How reliable are DOHC engines?

DOHC engine reliability varies based on overall design and maintenance, not just the DOHC configuration itself; while DOHC engines have more parts and can be more complex to maintain, they offer performance advantages and can be very reliable when properly cared for with regular oil changes and timely replacement of worn components. Key areas to monitor can include timing chains and valve cover gaskets, but addressing minor issues early can prevent major repairs and ensure a long lifespan for the engine. 
Why DOHC engines can be reliable 

• Precise valve control: The dual camshafts allow for independent control of intake and exhaust valves, leading to more efficient combustion and better performance.
• Better airflow: More valves per cylinder (typically four instead of two) improve the flow of air and exhaust gases, which enhances power and efficiency.
• High-RPM performance: DOHC designs are well-suited for higher revolutions per minute (RPM), which is crucial for performance and can contribute to engine longevity when operating within its designed parameters.

Why DOHC engines may seem less reliable

• Increased complexity: More parts, like two camshafts, additional valvetrain components, and more valves, mean greater complexity compared to SOHC (single overhead cam) engines. 
• More points of failure: With more moving parts, there are potentially more components that could wear out over time. 
• Maintenance costs: The added complexity can lead to higher maintenance and repair costs. 

Factors influencing DOHC engine reliability

• Maintenance schedule: Adhering to a regular maintenance schedule, especially oil changes with the correct type of oil, is crucial for longevity. 
• Quality of components: The specific design and quality of the engine’s components, including the timing chain, tensioners, and valve seals, play a significant role. 
• Driving conditions: How the vehicle is driven, particularly at high speeds or under heavy loads, can impact engine wear. 
• Specific engine model: Some DOHC engines are known for being particularly robust, while others may have common issues that require attention, such as timing chain wear or leaks. 

In summary
A DOHC engine’s reliability is less about the DOHC configuration itself and more about the overall engineering, quality of components, and adherence to a proper maintenance plan. While they are generally built for performance, with consistent and appropriate care, DOHC engines can be quite dependable and achieve high mileage.