What Is an Overhead Cam Engine?

An overhead cam (OHC) engine places its camshaft in the cylinder head above the combustion chamber, allowing it to open and close the valves directly or via short rocker arms—typically enabling higher RPM capability, finer valve control, and better efficiency than cam-in-block (pushrod) designs. In modern cars and motorcycles, OHC—especially double overhead cam (DOHC)—dominates because it supports multi-valve layouts and advanced technologies like variable valve timing and lift.

Contents

How an Overhead Camshaft Works
SOHC vs. DOHC
OHC vs. OHV (Pushrod) Designs
Advantages and Trade-offs
Cam Drive Methods
Modern Features Enabled by OHC
Maintenance and Reliability
Where You’ll Find OHC Engines Today
History in Brief
Common Misconceptions
Summary

How an Overhead Camshaft Works

In an OHC engine, the camshaft converts the crankshaft’s rotation into precise valve motion via a timing belt, chain, or gears. Because the cam sits in the head, the path from cam lobe to valve is short and rigid, reducing valvetrain mass and flex. This makes stable high-RPM operation and accurate timing adjustments easier, improving performance, emissions, and fuel economy.

Valve Actuation Path

As the crankshaft turns, a timing drive rotates the camshaft. Cam lobes press on followers—such as direct-acting tappets (buckets) or finger rockers—to open intake and exhaust valves against spring pressure. When the cam lobe rotates away, the spring closes the valve. Many OHC systems integrate hydraulic lash adjusters for reduced maintenance; some high-performance setups use solid lifters that require periodic clearance adjustments.

The following list outlines the key components commonly found in OHC valvetrains and how they contribute to precise valve control.

Camshaft(s) in the cylinder head: Single (SOHC) or dual (DOHC)

Followers: Bucket tappets or roller finger rockers to reduce friction

Valve springs: Close the valves and maintain contact with the cam profile

Timing drive: Belt, chain, or gears synchronize cam and crank

Variable valve timing (VVT) and lift systems: Adjust timing and lift dynamically

Together, these parts allow the OHC layout to precisely meter airflow, which is central to combustion efficiency and responsive power delivery.

SOHC vs. DOHC

Single Overhead Cam (SOHC)

SOHC designs typically use one camshaft per head to operate both intake and exhaust valves. They are compact and can be lighter and simpler, though they may offer fewer options for variable timing and multi-valve tuning compared with DOHC configurations.

Double Overhead Cam (DOHC)

DOHC uses separate cams for intake and exhaust valves, often enabling four valves per cylinder. This arrangement improves breathing at high RPM, eases the implementation of independent cam phasing, and is now the most common layout in modern passenger vehicles worldwide.

The list below compares typical traits of SOHC and DOHC to help clarify where each shines.

SOHC: Simpler packaging, potentially lower cost, adequate for two or three valves per cylinder

DOHC: Better airflow with four valves per cylinder, finer control via independent phasing, often higher peak power

In practice, automakers choose SOHC or DOHC based on targets for performance, cost, packaging, and emissions—not on a single metric like horsepower alone.

OHC vs. OHV (Pushrod) Designs

Overhead valve (OHV) or “pushrod” engines place the camshaft in the engine block and use long pushrods and rockers to actuate valves. OHC shortens this pathway by moving the cam into the head. Both designs can be powerful and efficient, but they trade off different strengths.

The following list highlights key differences between OHC and OHV architectures.

Valvetrain mass: OHC generally lower, aiding high-RPM stability

Packaging: OHV often shorter and more compact vertically, useful in trucks

Multi-valve support: DOHC naturally accommodates four valves per cylinder

VVT integration: Typically easier and more flexible with OHC

Manufacturing cost: OHV can be cheaper and simpler; OHC heads are more complex

While OHC dominates modern cars globally, notable OHV engines remain—such as GM’s small-block V8 and Stellantis’s Hemi V8—valued for compact size and strong low-end torque in trucks and performance applications.

Advantages and Trade-offs

OHC engines provide several tangible benefits that align with today’s priorities of efficiency, refinement, and performance.

Higher rev capability thanks to reduced valvetrain inertia

Better breathing with multi-valve heads for improved power and economy

Precise timing control enabling advanced VVT/VVL for emissions and drivability

Often smoother and quieter operation with modern roller followers and hydraulic lash

These strengths help explain why OHC—especially DOHC—is the default choice across most modern passenger vehicles and motorcycles.

OHC designs also introduce trade-offs that engineers must manage.

More complex cylinder heads can increase cost and height

Timing belts require scheduled replacement; chains can stretch and need tensioner care

Some are “interference” designs: timing failure can cause valve-to-piston contact

Tight packaging in transverse engine bays can complicate service access

Manufacturers address these issues with robust chain systems, oil-jetting for chain lubrication, long-life belts (including “wet belts” in oil on some engines), and designs that balance performance targets with lifetime maintenance expectations.

Cam Drive Methods

The cam drive keeps the camshaft synchronized to the crankshaft, typically at half engine speed. The choice affects durability, noise, and service intervals.

The following list outlines common drive systems and their characteristics.

Timing belt: Quiet and efficient; requires periodic replacement (often 60,000–105,000 miles or per manufacturer guidance)

Timing chain: Long service life and compact packaging; can stretch and requires robust tensioners and guides

Gear drive: Extremely precise and durable but heavy, noisy, and costly; seen in some performance and industrial engines

Wet belt (belt-in-oil): Reduces friction and noise; longevity depends on oil quality and design—service intervals vary by manufacturer

No single method is universally superior; automakers select the drive based on cost, packaging, NVH (noise, vibration, harshness), and durability targets.

Modern Features Enabled by OHC

With the cam in the head, OHC engines readily adopt technologies that fine-tune airflow for efficiency and performance.

The list below summarizes key features commonly paired with OHC architectures.

Variable valve timing (VVT) and dual independent cam phasing for intake and exhaust

Variable valve lift (e.g., Honda VTEC, BMW Valvetronic, Nissan VVEL) to reduce throttling losses

Multi-valve combustion chambers for better swirl/tumble and emissions control

Turbocharging compatibility with optimized valve timing for low-lag response

These systems allow engines to deliver strong torque at low RPM and high power at the top end, while meeting strict global emissions standards.

Maintenance and Reliability

OHC engines can be very durable when serviced per schedule. Awareness of timing components and valve adjustments is key.

The following list covers typical maintenance considerations for OHC engines.

Timing belts: Replace at or before the specified interval to avoid failure

Timing chains: Listen for rattle on cold start; address tensioner or guide wear early

Valve clearance: Some DOHC engines with solid lifters need periodic checks/adjustments

Oil quality: Critical for hydraulic tensioners, VVT actuators, and roller followers

Cooling system health: Prevents head warpage and head-gasket issues

Following the manufacturer’s service intervals and using the correct oil grade helps extend the life of timing components and valvetrain mechanisms.

Where You’ll Find OHC Engines Today

Most modern passenger cars and motorcycles use OHC—predominantly DOHC—across mainstream and premium brands. Turbocharged DOHC four-cylinders are now common globally, while performance and luxury models often add direct injection and advanced valve control. In contrast, many small utility engines (like lawn equipment) still use simpler OHV pushrod designs for cost and durability reasons.

The list below gives real-world examples of OHC prevalence.

Automakers: Toyota, Honda, Hyundai/Kia, BMW, Mercedes-Benz, Ford, Nissan, Subaru—mostly DOHC across lineups

Motorcycles: Widespread DOHC use (e.g., Ducati, Yamaha, Kawasaki); some unique systems like Ducati’s desmodromic DOHC

Exceptions: GM small-block and Stellantis Hemi V8s remain OHV in many trucks/performance cars

This distribution reflects how OHC suits modern emissions and efficiency targets, while OHV persists where compact packaging and specific torque characteristics are prized.

History in Brief

OHC technology dates to the early 20th century in racing—famously in pre–World War I Grand Prix cars—before trickling into production vehicles mid-century. By the 1980s and 1990s, tightening emissions rules and the push for better specific output made OHC and multi-valve heads mainstream. Today, OHC defines the modern internal-combustion architecture in most markets.

Common Misconceptions

Because OHC is widespread, it’s easy to assume it’s universally “better,” but context matters.

“OHC is always faster”: Not necessarily; some OHV engines deliver exceptional performance and torque

“Chains never need service”: Chains can stretch; tensioners and guides wear

“All OHC engines are interference designs”: Many are, but not all—design varies by engine

“DOHC is always more efficient than SOHC”: Efficiency depends on tuning, combustion design, and controls—not just cam count

The best architecture depends on goals: packaging, cost, emissions strategy, performance, and intended duty cycle.

Summary

An overhead cam engine places the camshaft in the cylinder head to actuate valves directly or through short rockers, enabling precise timing, high-RPM stability, and multi-valve efficiency. DOHC setups dominate modern vehicles due to their flexibility with variable timing and lift systems, although OHV designs still thrive in niches that value compact packaging and low-end torque. The result is a technology that underpins today’s balance of performance, fuel economy, and emissions compliance across the automotive and motorcycle worlds.

Are overhead cam engines good?

“Overhead camshaft engines can produce higher performance but typically cost more to build. Pushrod engines are cheaper to build and work on. Many engines use overhead camshaft designs because the optimum cylinder head design allows for increased fuel economy and performance too.”

Which is better, OHV or OHC engine?

Neither OHV nor OHC is inherently better; the choice depends on the application’s priorities, with OHV (Overhead Valve) engines favored for their compact size, lower-end torque, and rugged durability, and OHC (Overhead Cam) engines preferred for higher RPMs, greater fuel efficiency, and more power potential due to their more direct and efficient valve train.

This video explains the differences between OHV, SOHC, and DOHC engines: 59sEngineering ExplainedYouTube · Dec 27, 2024
Choose OHV (Pushrod) for:

Low-end torque and ruggedness: OHV engines excel at producing strong torque at lower RPMs, making them ideal for trucks and American muscle cars.
Compact size and simpler design: The camshaft is in the engine block, resulting in a smaller, lighter engine package with fewer complex components.
Durability and ease of maintenance: OHV engines are known for their reliability and simpler maintenance.

Choose OHC (Overhead Cam) for:

Higher RPMs and power output: The camshaft’s placement in the cylinder head and direct actuation reduce valve train mass, allowing for higher engine speeds and more power.
Fuel efficiency and performance: OHC designs facilitate more valves per cylinder and improved airflow, leading to better volumetric efficiency, power, and fuel economy.
Flexibility: The ability to add multiple camshafts (SOHC/DOHC) and use variable valve timing enhances performance and response across a broader RPM range.

Key Differences Summarized

Feature	OHV (Overhead Valve)	OHC (Overhead Cam)
Camshaft Location	In the engine block	In the cylinder head
Valve Train	Uses pushrods and rocker arms	Direct actuation by the camshaft
Torque/Power Band	Strong low-end torque	Higher power and RPM potential
Complexity & Cost	Simpler, less complex, cheaper	More complex, heavier, costlier
Engine Size	More compact package	Larger cylinder head

What is an overhead cam in an engine?

Overhead Camshaft (OHC) Engines
Overhead Camshaft engines (OHC) are similar to OHV engines, but they also have their camshafts positioned in the cylinder head above the combustion chamber. This means they offer all the benefits of an OHV design and more.

What are the disadvantages of overhead cam engines?

A downside is that the system used to drive the camshaft (usually a timing chain in modern engines) is more complex in an OHC engine, such as the 4-chain valvetrain of the Audi 3.2 or the 2 meter chain on Ford cammers.