Post by Töuge-MR on Dec 23, 2005 0:36:47 GMT -5
OHV engine design (aka pushrod design)
4-cylinder 8 valves OHV engine
OHV means OverHead Valve - an engine design where the camshaft is installed inside the engine block and valves are operated through lifters, pushrods and rocker arms (an OHV engine also known as "Pushrod" engine). Although the OHV design is a bit outdated, especially with today's strict emission standards and high gas prices, it has been successfully used for many years. An OHV engine is very simple, has more compact size and proven to be durable. The downside is that it's difficult to precisely control the valve timing at high rpm due to larger inertia of all valve train components (lifter-pushrod-rocker arm). Also it's very difficult to instal more than 2 valves per cylinder or implement variable valve timing - something that could be easily done in an DOHC engine.
OHC or SOHC engine
4-cylinder 8 valves SOHC engine
OHC means OverHead Cam and SOHC means Single OverHead Cam. The design where the camshaft is installed in the cylinder head and valves are operated either by the rocker arms or directly through the lifters (as in the picture).
The advantage is that valves are operated almost directly by the camshaft - easy to set perfect timing at high rpm. Also it's asy to install three or four valves per cylinder
The disadvantage - an OHC engine requires a timing belt or chain - more complex and more expensive design.
DOHC or Twin cam engine
Typical 4-cylinder 16 vlaves DOHC engine
DOHC or Double OverHead Cam - the setup used in most today's cars. Since it's possible to install multiple valves per cylinder and place intake valves on the opposite side from exhaust vales, DOHC engine can "breath" better meaning that it can produce more horsepowers with smaller engine volume. Compare: The 3.5-liter V6 DOHC engine of 2003 Nissan Pathfinder has 240 h.p, similar to 245 h.p of the 5.9-liter V8 OHV engine of 2003 Dodge Durango.
Pros: High efficiency, possible to install multiple valves per cylinder and adopt variable timing.
Cons:More complex and more expensive design.
4-cylinder 8 valves OHV engine
OHV means OverHead Valve - an engine design where the camshaft is installed inside the engine block and valves are operated through lifters, pushrods and rocker arms (an OHV engine also known as "Pushrod" engine). Although the OHV design is a bit outdated, especially with today's strict emission standards and high gas prices, it has been successfully used for many years. An OHV engine is very simple, has more compact size and proven to be durable. The downside is that it's difficult to precisely control the valve timing at high rpm due to larger inertia of all valve train components (lifter-pushrod-rocker arm). Also it's very difficult to instal more than 2 valves per cylinder or implement variable valve timing - something that could be easily done in an DOHC engine.
OHC or SOHC engine
4-cylinder 8 valves SOHC engine
OHC means OverHead Cam and SOHC means Single OverHead Cam. The design where the camshaft is installed in the cylinder head and valves are operated either by the rocker arms or directly through the lifters (as in the picture).
The advantage is that valves are operated almost directly by the camshaft - easy to set perfect timing at high rpm. Also it's asy to install three or four valves per cylinder
The disadvantage - an OHC engine requires a timing belt or chain - more complex and more expensive design.
DOHC or Twin cam engine
Typical 4-cylinder 16 vlaves DOHC engine
DOHC or Double OverHead Cam - the setup used in most today's cars. Since it's possible to install multiple valves per cylinder and place intake valves on the opposite side from exhaust vales, DOHC engine can "breath" better meaning that it can produce more horsepowers with smaller engine volume. Compare: The 3.5-liter V6 DOHC engine of 2003 Nissan Pathfinder has 240 h.p, similar to 245 h.p of the 5.9-liter V8 OHV engine of 2003 Dodge Durango.
Pros: High efficiency, possible to install multiple valves per cylinder and adopt variable timing.
Cons:More complex and more expensive design.
