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OHV, OHC, SOHC and DOHC (twin cam) engine design

Updated: October 8, 2017

OHV or "Pushrod" engine

OHV engine animated diagram
4-cylinder 8-valve OHV engine
GM LSA 6.2L V8 engine
The GM 556-hp 6.2L LSA V8 OHV engine
used in the Cadillac CTS-V

OHV in general means OverHead Valve, or valves are installed in the cylinder head. Often the term "OHV" is used to describe the engine design where the camshaft is installed inside the engine block and valves are operated through lifters, pushrods and rocker arms. This design is also known as a "Pushrod" engine.
The OHV design has been successfully used for decades.

The main disadvantage of an OHV design is that it's difficult to precisely control the valve timing at high rpm. The reason for that is the higher inertia caused by a larger amount of valve train components (lifter-pushrod-rocker arm). This means, that an OHV design is better suited for V8 or larger engines, where large engine volume offers higher torque at lower rpms.

It's also technically more difficult to install more than 2 valves per cylinder, or implement Variable Valve Timing - something that could be easily done in a DOHC engine.

Advantages of an OHV engine include lower cost, proven durability, low-end torque and compact size. For example, the 2018 Chevrolet Corvette Z06 is 4.4 inches shorter than 2018 Honda Civic sedan. Yet, thanks to its compact 6.2L V8 OHV engine, the Corvette Z06 can go from 0 to 60 mph in 2.9 seconds. The Corvette's supercharged aluminum 650-hp OHV LT4 engine offers crazy 650 lb-ft of torque at 3600 rpm.

Today, with the pressure to make cars more efficient, you will only find an OHV engine in some trucks and V8-powered sports cars. Modern 4-cylinder and V6 cars and SUVs have either OHC or DOHC engines.

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OHC or SOHC engine

SOHC engine animated diagram
4-cylinder 8-valve SOHC engine

OHC means OverHead Cam in general, while SOHC means Single OverHead Cam or Single Cam.
In a SOHC engine the camshaft is installed in the cylinder head and valves are operated either by the rocker arms or directly through the lifters (as in this animation).

The main advantage of an OHC design is that valves are operated almost directly by the camshaft, which makes it easier to maintain precise timing at higher rpms. It's also possible to install three or four valves per cylinder. What cars use SOHC engines? What is the difference between SOHC and DOHC engine?

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