What a Dual Overhead Cam (DOHC) Looks Like

A dual overhead cam (DOHC) engine has two camshafts mounted on top of the cylinder head; visually, you’ll see a wide, flat valve cover (often labeled “DOHC” or “16V”) and, when the cover is removed, two long, parallel camshafts with lobes running the length of the head, plus timing sprockets and a chain or belt at one end. In daily use, you mostly notice the broad cam/valve cover and the front timing cover; inside, the twin cams sit directly above the intake and exhaust valves to operate them with precision.

What DOHC Means and Where It Sits

In a DOHC layout, both camshafts are located “overhead” in the cylinder head: one cam typically actuates the intake valves and the other the exhaust valves. This arrangement can be on a single cylinder head (inline engines) or on each bank of a V-type engine (resulting in four cams total for a V6/V8, two per bank). The visual signature: two cams per head, mounted in a rigid line along the head, with timing hardware at one end.

What You’ll See With the Engine Assembled (Valve Cover On)

From outside the engine, the DOHC architecture reveals itself through several common cues, even without disassembly. The features below are the most consistent visual indicators you can spot in an engine bay.

• A wide, flat valve cover spanning the cylinder head, often relatively large compared with pushrod engines.
• “DOHC,” “Twin Cam,” or valve-count markings like “16V,” “24V,” or “32V” cast or printed on the cover.
• Coil-on-plug modules or spark plug wells positioned down the centerline of the valve cover (especially on inline-4s), indicating centrally located spark plugs.
• A prominent timing belt or chain cover at the front (or side, depending on engine orientation), sometimes bulged to accommodate two cam sprockets.
• Symmetrical intake and exhaust manifolds on opposite sides of the head in many designs, reflecting the split roles of the two cams.

While external styling varies by manufacturer, these traits collectively point to a DOHC head, especially the combination of a broad cam cover and a front timing enclosure large enough for twin cam gears.

What You’ll See With the Valve Cover Removed

With the cover off, the architecture is unmistakable. Below are the core elements you’d visually identify when looking directly at a DOHC cylinder head.

• Two long, parallel camshafts running the length of the head—one for intake valves, one for exhaust.
• Cam lobes shaped like offset ovals along each shaft that press on followers/buckets to open valves.
• Cam caps or bearing bridges bolted across the cams at intervals, holding them in precise alignment.
• Timing sprockets (gears) at one end of the cams, linked by a chain or belt to the crankshaft; many modern engines also show variable valve timing (VVT) “phasers” integrated into the sprockets.
• Valve actuation hardware: bucket tappets (common), finger followers, or small rocker arms between lobes and valves.
• Visible valve springs and retainers around each valve stem, typically arranged in two tidy rows.

Together, these pieces form a clean, symmetrical layout: two cam lines above two neat rows of valves, with timing hardware anchoring one end—precisely the image most people associate with a modern performance-oriented head.

How DOHC Looks on Different Engine Types

Inline Engines (I-4, I-6)

Inline engines have one cylinder head, so you’ll see a single wide valve cover with two cams beneath. Externally, expect a compact, rectangular top profile with central spark plug access and a front timing cover that often rises high enough to house two cam sprockets.

V Engines (V6, V8, V10)

V engines use two cylinder heads, one per bank. Each head has its own pair of cams, resulting in four camshafts total on a DOHC V6 or V8. Visually, you’ll see two separate valve covers—one per bank—often with mirrored timing hardware at the front of each bank.

How to Tell DOHC from Other Common Valvetrain Layouts

It’s easy to confuse valvetrain types without knowing the telltale signs. The points below help distinguish DOHC from SOHC and pushrod (OHV) setups at a glance.

• SOHC (Single Overhead Cam): Only one cam per head. Under the cover you’ll see a single camshaft centered above both intake and exhaust valves; externally, timing covers are often smaller, and valve count markings may read “12V” on an I-4 or “24V” on a V6.
• OHV/Pushrod: No cams in the head—just rocker arms and pushrods; the camshaft sits inside the engine block. Valve covers are often tall and narrow on V engines, and the front timing cover is typically more compact, since it doesn’t house cam sprockets up top.
• Visual shorthand: DOHC heads appear broad and symmetrical with two visible cam lines (when open) and larger timing housings; pushrod engines lack twin cam sprockets at the head level entirely.

Using these cues, you can quickly narrow down what you’re looking at without needing to fully dismantle the engine.

Modern Details You Might Notice

Recent DOHC engines commonly incorporate technologies that add distinctive visual features. Here are elements you may spot on newer designs.

• Cam phasers on the ends of the camshafts—slightly bulkier, finned, or sealed units integrated with the sprockets for variable valve timing.
• Integrated cam carrier assemblies—an upper “ladder” structure that supports both cams under a single casting for rigidity and oil control.
• Direct injection hardware—high-pressure fuel rail and injectors often passing through the head, sometimes between the cam lines.
• Plastic or composite cam covers with molded baffles and integrated PCV systems, making the top surface smoother and more uniform.

These additions don’t change the core DOHC look—two cams up top—but they help explain why some modern heads appear more compact or enclosed.

Common Misidentifications and Tips

Because manufacturers vary styling, some engines can trick the eye. The notes below help avoid common ID mistakes when assessing appearance.

• “Twin cam” vs “DOHC”: In common usage, they’re the same for an inline engine. On a V engine, “twin cam” could describe each head; combined, it’s four cams across the engine.
• Decorative engine covers: Many cars have cosmetic covers that hide the real valve cover—remove the plastic top to see the actual cam/valve cover shape.
• Coil pack placement: Coil-on-plug modules centered on the valve cover often coincide with DOHC layouts, but verify by checking for a large front timing cover or the presence of two cam sprockets if accessible.

When in doubt, look for the structural essentials: two cam lines under the cover and twin cam sprockets connected to the timing chain or belt.

Bottom Line Visual

Think of a DOHC head as a tidy, symmetrical top end: a broad valve cover on the outside, and—once opened—two parallel camshafts with rows of cam lobes, cam caps, and valves beneath, plus sizable timing hardware at one end. On V engines, you’ll see that same arrangement duplicated on each bank.

Summary

A dual overhead cam engine places two camshafts atop each cylinder head—one for intake, one for exhaust—producing a broad valve cover profile and, under the cover, two parallel camshafts with lobes, caps, and timing sprockets (often with VVT phasers). Inline engines have a single DOHC head; V engines have two DOHC heads. Externally, look for a large cam cover and a prominent timing cover; internally, the unmistakable twin-cam layout defines the look.

How can I identify a DOHC engine?

Single Overhead Camshaft or known as SOHC and Dual Overhead Camshaft abbreviated as DOHC. Inside the engine cylinder, SOHC only has 1 overhead camshaft, while DOHC has 2 camshafts.

What is the benefit of a dual cam?

Dual Coverage: The Ultimate Advantage
Capturing the front and rear views provides a 360-degree perspective that single-channel cams simply cannot match. This comprehensive coverage is particularly valuable in hit-and-run incidents or when dealing with tailgating drivers, offering undeniable proof of what happened.

What does a double overhead cam look like?

So the same piece pushes down the the two valves per cylinder uh a little more complex. But in many ways uh much lighter makes a lot more horsepower. And all modern motors use these things.

What is the difference between single overhead cam and dual overhead cam?

Single overhead camshaft (SOHC) engines use one camshaft to operate both intake and exhaust valves for simpler design, lower cost, and better fuel efficiency, while dual overhead camshaft (DOHC) engines use two separate camshafts, allowing for more valves per cylinder, better airflow, increased horsepower, higher RPMs, and precise valve control. The choice between SOHC and DOHC depends on priorities, with SOHC favoring cost-effectiveness and efficiency, and DOHC excelling in performance and power.
 
This video explains the differences between SOHC and DOHC engines: 58sThe Engineers PostYouTube · Jul 1, 2023
Single Overhead Camshaft (SOHC)

• Operation: One camshaft in the cylinder head operates both intake and exhaust valves. 
• Advantages:
  • Cost-Effective: Fewer components lead to lower manufacturing costs. 
  • Fuel Efficient: Less weight and friction result in better fuel economy. 
  • Simpler Design: Less complex and easier to maintain. 
  • Good Low-RPM Torque: Often produces better torque at lower engine speeds. 
• Disadvantages:
  • Limited Airflow: Fewer intake and exhaust valves restrict airflow, potentially limiting top-end power. 
  • Less Precise Control: Less control over valve timing compared to DOHC. 

Dual Overhead Camshaft (DOHC) 

• Operation: Two separate camshafts in the cylinder head—one for intake valves and one for exhaust valves—are used. 
• Advantages:
  • Improved Airflow: More valves per cylinder allow for better intake and exhaust gas flow, leading to increased engine power. 
  • Higher Power: Better volumetric efficiency results in higher horsepower and top-end torque. 
  • Higher RPM Limit: The more direct valve operation reduces inertia forces, allowing for higher engine revolutions. 
  • Optimal Spark Plug Placement: The DOHC design allows the spark plug to be placed in the center of the combustion chamber for more efficient combustion. 
  • Advanced Technologies: Facilitates implementation of efficiency-enhancing technologies like Variable Valve Timing (VVT). 
• Disadvantages:
  • Higher Cost: More components and complexity increase manufacturing and production costs. 
  • Increased Weight: More moving parts add weight and increase parasitic power loss. 
  • Potential for Lower Low-End Torque: Without technologies like VVT, DOHC engines might have less torque at low RPMs compared to SOHC engines. 

Which is Better?
There’s no universal “better” choice; it depends on your priorities. 

• Choose SOHC for: Opens in new tabBudget-conscious drivers and everyday driving, where fuel efficiency and lower maintenance costs are more important. 
• Choose DOHC for: Opens in new tabPerformance-oriented driving and higher horsepower, as it provides better power delivery at high RPMs and more precise engine control.