DOHC Disadvantages: What Owners, Buyers, and Builders Should Know

Double overhead camshaft (DOHC) engines generally cost more, take up more space, carry slightly higher frictional losses, can be harder to service, and may trade a bit of low‑RPM torque for high‑RPM power if not offset by modern controls. In brief: added complexity, size, and parts bring potential gains but also more to manage, pay for, and maintain. This article explains how those drawbacks show up in the real world and why many automakers still choose DOHC despite them.

What DOHC Means

DOHC places two camshafts per cylinder bank—one for intake valves and one for exhaust—on top of the cylinder head. The layout enables optimal valve placement, higher valve lift and duration potential, and independent control of intake and exhaust timing. It’s common in modern cars and motorcycles because it supports high specific output, cleaner combustion, and broad tuning flexibility compared with single overhead cam (SOHC) or overhead valve (OHV/pushrod) designs.

The Main Disadvantages of DOHC

Below are the primary downsides most often cited by engineers, mechanics, and owners, with context for how each can affect purchasing and ownership decisions.

• Higher manufacturing cost and parts count: Two camshafts per bank, more bearings, caps, phasers (when equipped), and a longer or more complex chain/belt drive raise material and machining costs.
• Larger size and packaging constraints: DOHC cylinder heads are typically wider and taller, which can complicate engine-bay packaging, raise the engine’s installed height, and crowd ancillary components.
• More friction and parasitic losses: Extra cam bearings, followers, seals, and a longer chain or belt can increase mechanical drag, slightly reducing net efficiency compared with simpler valvetrains.
• Weight and rotational inertia: Added hardware in the head can increase engine mass; while camshaft inertia is modest, total system weight can affect vehicle weight distribution and serviceability.
• Service complexity and labor time: Valve clearance checks (where applicable), timing alignment across dual cams, and phaser maintenance are more time-consuming than on SOHC or OHV engines.
• More potential failure points: Additional phasers, chain guides, tensioners, cam seals, and bearings introduce more items that can wear, leak, or fail over high mileage if maintenance is neglected.
• Potential low‑RPM torque tradeoffs without advanced controls: DOHC architectures often favor high‑RPM breathing; without variable valve timing/lift, they can feel softer at low revs compared with simpler, small‑port designs.
• Noise, vibration, and harshness (NVH) considerations: Longer chains and more moving parts can introduce rattles or whine as components age, though modern design mitigations help.

Collectively, these factors don’t negate DOHC’s benefits, but they shape cost, packaging, and maintenance realities that buyers and owners should weigh against performance and efficiency goals.

Real-World Impacts

Cost of Ownership

Beyond higher purchase prices, DOHC engines can incur added maintenance costs: more frequent or involved timing-service work, pricier phasers when fitted, and less DIY-friendly valve adjustments on certain designs. Reliability remains strong in many modern DOHC engines, but deferred oil changes or low-quality lubricants can accelerate wear in chains, guides, and cam phasers.

Fuel Economy and Emissions

On paper, added valvetrain friction is a small drag on efficiency. In practice, DOHC engines often offset this with superior breathing, higher compression ratios, and wide-range variable valve timing, resulting in competitive or better fuel economy and emissions. The net effect depends on the engine’s calibration and how it’s used (city short trips vs. steady highway cruising, for example).

Performance and Drivability

DOHC enables strong high‑RPM power and clean combustion, which is why it’s common in performance and high-specific-output engines. Without advanced timing control or variable lift, some DOHC engines can feel less torquey at low revs; modern multi-phaser systems largely mitigate this by optimizing valve timing across the rev range.

When DOHC Might Not Be the Best Choice

While DOHC is versatile, there are scenarios where its tradeoffs outweigh its advantages, and simpler valvetrains may be preferable.

1. Budget-focused commuter vehicles where lowest manufacturing and maintenance costs are paramount and performance targets are modest.
2. Tight engine bays (small cars, transverse layouts) where head height/width and accessory access are pressing constraints.
3. Use cases prioritizing low-end torque and simplicity (e.g., basic utility engines), where OHV/SOHC designs can deliver adequate performance with fewer parts.
4. Applications demanding extreme field serviceability and durability (generators, small industrial engines), where fewer moving parts simplify upkeep.

In these situations, the simplicity and lower cost of SOHC or OHV can be compelling, especially when absolute top-end power or broad cam phasing isn’t required.

How Automakers Mitigate These Drawbacks

Modern engineering has reduced many of DOHC’s historical penalties through materials, design integration, and smarter controls.

• Advanced valve control: Wide-range variable valve timing (on both cams) and variable valve lift restore low-end torque and broaden efficiency.
• Lightweight, low-friction parts: Hollow camshafts, roller finger followers, DLC coatings, and optimized spring rates cut mass and drag.
• Compact head architecture: Integrated cam carriers, narrower included valve angles, and modular timing covers improve packaging and service access.
• Durable timing systems: Improved chains, guides, and tensioners, plus better oiling strategies, extend service intervals and quiet NVH.

These strategies don’t erase complexity but make modern DOHC engines more reliable, efficient, and maintenance-friendly than earlier generations.

Bottom Line

DOHC’s disadvantages center on complexity, cost, packaging, friction, and maintenance. For many buyers, the performance, efficiency headroom, and tuning flexibility outweigh those drawbacks—especially with today’s robust variable valve technologies. Still, understanding the tradeoffs helps you choose the right engine for your needs and budget.

Summary

DOHC engines can be more expensive, bulkier, and slightly less efficient mechanically due to added friction, with more components to service and potential low‑RPM softness if not paired with modern variable valve systems. Automakers mitigate these issues with advanced timing, lightweight parts, and compact designs, making DOHC a strong choice for performance and efficiency—so long as you accept the added complexity and cost.

Is the DOHC engine reliable?

DOHC engines are generally reliable and offer high performance and efficiency, but their reliability heavily depends on proper maintenance, including regular oil changes and timely replacement of worn components like timing belts or chains. Common issues that can arise are timing chain or belt wear, valve cover gasket leaks, and, in specific models, problems with variable valve timing (VVT) systems. Adhering to the manufacturer’s recommended maintenance schedule is crucial to prevent issues and ensure a long lifespan for a DOHC engine.
 
Factors Affecting DOHC Engine Reliability

• Maintenance History: A well-maintained engine, with documented service records, is more likely to be reliable. 
• Age and Mileage: Like any engine, older DOHC engines with high mileage may experience more wear and tear. 
• Specific Model and Engine Design: Reliability can vary significantly between different DOHC engines and manufacturers; some designs are known for specific issues. 

Common DOHC Engine Issues

• Timing Chain/Belt Problems: Opens in new tabWear and tear on the timing chain or belt, and its tensioners, can lead to rattling noises or misalignment, potentially causing engine misfires or damage if not addressed. 
• Valve Cover Gasket Leaks: Opens in new tabOver time, valve cover gaskets can degrade, leading to oil seepage around the engine. 
• Variable Valve Timing (VVT) Issues: Opens in new tabIn some models, problems with the VVT system, such as faulty sensors or components, can lead to performance issues or the check engine light coming on. 
• Oil Consumption: Opens in new tabCertain DOHC engines may exhibit increased oil consumption, especially if maintenance history is poor or if there are leaks, leading to potential damage if not topped off. 

How to Maintain a Reliable DOHC Engine

• Follow the Maintenance Schedule: Adhere strictly to the manufacturer’s recommended intervals for oil changes and other services. 
• Check Fluid Levels: Regularly inspect and maintain proper levels of engine oil and coolant. 
• Address Leaks Promptly: Fix minor oil or coolant leaks as soon as they appear to prevent more significant damage. 
• Listen for Unusual Noises: Pay attention to any new or unusual sounds, such as ticking or rattling, which can signal a developing problem. 

Which is better, SOHC or DOHC?

Compared to SOHC engines, DOHC motors produce more power because there is less inertia. You will experience more torque if you move the driving rod faster. Double camshafts allow you to adjust the intake and exhaust valves separately.

What are the disadvantages of a DOHC engine?

Disadvantages of DOHC (Dual Overhead Camshaft) engines include higher manufacturing costs and increased complexity, leading to more expensive and complex maintenance and repair. They are generally heavier and taller, requiring more components and contributing to greater engine complexity. Additionally, they can have less efficient fuel consumption and lower low-end torque compared to SOHC engines, and they are more susceptible to mechanical noise and potential timing belt failure.
 
Cost and Complexity

• Higher manufacturing costs: Opens in new tabThe addition of a second camshaft and associated components increases the overall complexity of the engine, which in turn raises manufacturing costs. 
• Increased complexity and maintenance: Opens in new tabDOHC engines have more complex valve train systems, including a more complex timing belt or chain drive system, which adds to maintenance needs and expenses. 

Engine Design and Weight 

• Heavier and taller: DOHC engines tend to be heavier and physically taller than single overhead camshaft (SOHC) engines, which can impact vehicle design and space requirements. 
• More components: The need for two camshafts and their associated components adds more parts to the overall engine assembly. 

Performance and Efficiency

• Lower low-end torque: The complex valve train can make DOHC engines less responsive and produce less torque at lower RPMs compared to some other designs. 
• Parasitic power loss: Spinning the additional camshaft and valve train components requires more power from the crankshaft, leading to parasitic power loss and potentially lower maximum engine RPMs. 
• Fuel inefficiency: Due to the added friction and the need for more components to operate, DOHC engines can be less fuel-efficient, especially at lower RPMs. 

Potential for Noise and Failure 

• More mechanical noise: The increased number of moving parts in the valve train can contribute to higher levels of mechanical noise. 
• Increased risk of failure: With more components, there are more potential points of failure, and issues with the complex timing mechanism can lead to significant engine damage. 

What is the point of DOHC?

Dual overhead cam engines are found in most modern vehicles today. They allow better airflow with less obstruction and are generally much more efficient engines than OHV or SOHC engines. Two camshafts operate 4 valves per cylinder, one separate camshaft for intake and exhaust valves.