What Type of Camshaft Is DOHC?

DOHC stands for Double Overhead Camshaft: it’s an overhead-cam valvetrain layout with two camshafts per cylinder head—typically one operating the intake valves and the other the exhaust valves. In an inline engine that means two cams total; in a V-type engine it means four cams (two per bank). This configuration improves breathing, allows more precise valve timing, and commonly supports four valves per cylinder.

What DOHC Means and How It Works

In a DOHC design, both camshafts sit above the combustion chambers within the cylinder head. One camshaft actuates the intake valves, while the other operates the exhaust valves, usually through cam followers or tappets and, in many modern engines, with hydraulic lash adjustment. The cams are driven by a timing chain or belt and often paired with variable valve timing systems that can phase each cam independently for better power, efficiency, and emissions control across the rev range.

How DOHC Compares to Other Camshaft Layouts

Understanding DOHC is easier when contrasted with other common valvetrain arrangements found in road cars and motorcycles.

• OHV (Overhead Valve/pushrod): The camshaft sits in the engine block and uses pushrods and rocker arms to open valves. It’s compact and rugged but typically limits high-RPM breathing.
• SOHC (Single Overhead Cam): One camshaft per head operates both intake and exhaust valves. It’s simpler than DOHC, often with fewer parts, but offers less flexibility for advanced valve timing strategies.
• DOHC (Double Overhead Cam): Two cams per head, with separate intake and exhaust control, enabling higher valve lift/area, better timing optimization, and usually four valves per cylinder.

While all three can be effective, DOHC provides the most headroom for airflow and timing sophistication, which is why it dominates modern performance and efficiency-focused designs.

Advantages of DOHC

Manufacturers widely adopt DOHC because it unlocks performance and efficiency benefits without sacrificing drivability.

• Improved airflow: Separate cams and multi-valve heads increase intake/exhaust flow, boosting power and response.
• Higher RPM capability: Reduced valvetrain inertia and better valve control support higher engine speeds.
• Advanced variable timing: Independent phasing of intake and exhaust cams broadens torque curves and enhances fuel economy.
• Cleaner emissions: Precise valve control aids combustion efficiency and aftertreatment performance.
• Optimized combustion: Multi-valve layouts enable central spark-plug placement and efficient chamber design.

These attributes make DOHC well-suited to modern emissions standards and consumer expectations for both power and efficiency.

Trade-offs and Considerations

DOHC is not without drawbacks, especially in packaging and maintenance contexts.

• Complexity and cost: More parts and tighter tolerances can increase manufacturing and repair costs.
• Packaging: Twin cams and wider cylinder heads can make engines larger and sometimes heavier at the top end.
• Frictional losses: Additional cam journals and valve-train components can slightly raise mechanical drag.
• Service access: Timing components and valve gear can be more labor-intensive to service or replace.

Despite these trade-offs, efficiency gains and regulatory pressures keep DOHC prevalent in new engine designs.

Common Applications and Examples

From economy cars to superbikes, DOHC is the mainstream choice for modern high-efficiency and high-output engines.

• Passenger cars: Toyota Dynamic Force four-cylinders, Honda K-series, Mazda Skyactiv-G, Hyundai/Kia Smartstream, and BMW’s B-series inline engines.
• Performance/V engines: Ford 5.0L Coyote V8, Mercedes-AMG and BMW M twin-cam heads per bank, many modern Ferraris and Lamborghinis.
• Motorcycles: High-revving sport bikes (e.g., Yamaha YZF, Honda CBR, Kawasaki Ninja families) commonly use DOHC for precise valve control.

Across these segments, DOHC supports wide torque bands, high specific output, and modern emissions compliance.

How to Identify a DOHC Engine

If you’re unsure whether an engine is DOHC, a few visual and documentation checks help confirm it.

• Valve covers: Inline engines usually have a single head with a wide cover; V engines have two covers—look for indications of two camshafts per head.
• Markings: Many manufacturers label “DOHC,” “Twin Cam,” or similar on the cover or intake shroud.
• Timing sprockets: Service diagrams or a peek under the cover often reveal two cam sprockets per head.
• Valve count: Four valves per cylinder is common in DOHC engines, though not exclusive to them.
• Owner’s manual/spec sheet: Official documentation will list the valvetrain as DOHC.

A quick combination of visual cues and documentation typically settles the question definitively.

Summary

DOHC—Double Overhead Camshaft—is an overhead-cam valvetrain with two camshafts per cylinder head, one for intake and one for exhaust. It enables superior airflow, high-RPM capability, and flexible variable valve timing, making it the dominant architecture in modern gasoline and many motorcycle engines. While more complex and sometimes costlier than SOHC or OHV designs, its performance and efficiency advantages have made it a near-universal choice in contemporary powertrains.

What is an OHV camshaft?

OHV or Overhead Valve
The camshaft activates pushrods that move up and down to operate rocker arms that open and close the valves in the cylinder head. OHV engines, also called pushrod engines, can produce lots of torque at low engine speeds but can’t run at the same high engine speeds as overhead-camshaft engines.

Which is better DOHC or SOHC?

An engine with a DOHC design can produce more horsepower than a SOHC design. Lower Band Torque: SOHC engines produce more torque at the lower ends because they are lighter than DOHC engines. SOHC bikes offer the best mileage as a result. Weight: SOHC engines typically have two or three valves per cylinder.

What type of cam is DOHC?

Dual overhead camshaft (DOHC)
A dual overhead cam, double overhead cam, or twin-cam engine has two camshafts over each bank of the cylinder head, one for the intake valves and another for the exhaust valves.

How to tell SOHC vs DOHC?

The difference is exactly what you would think. In a SOHC there is one cam that actuates both the intake and exhaust valves. In a DOHC there is a cam for the intake valves and the exhaust valves. The advantage is that it is easier to change the timing of the intake and exhaust cams when they are seperate.