OHV, OHC, SOHC and DOHC (twin cam) engine design
OHV old engine design
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 a "Pushrod" engine). Although an OHV
design is a bit outdated, it has been successfully used for decades. An
OHV engine is very simple, it has more compact
size and is proven to be durable.
On the downside, it's difficult to precisely control the valve timing at high rpm due to higher inertia caused by larger amount of valve train components (lifter-pushrod-rocker arm). Also, it's very difficult to install more than 2 valves per cylinder, or implement some of the latest technologies such as Variable Valve Timing - something that could be easily done in a DOHC engine.
On the downside, it's difficult to precisely control the valve timing at high rpm due to higher inertia caused by larger amount of valve train components (lifter-pushrod-rocker arm). Also, it's very difficult to install more than 2 valves per cylinder, or implement some of the latest technologies such as Variable Valve Timing - something that could be easily done in a DOHC engine.
OHC
or SOHC
New
engine
design
OHC
in general means Overhead Cam while SOHC means Single Overhead 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 the picture).
The advantage is that valves are operated almost directly by the camshaft, which makes it easy to achieve the perfect timing at high rpm.
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 the picture).
The advantage is that valves are operated almost directly by the camshaft, which makes it easy to achieve the perfect timing at high rpm.
DOHC
or Twin
Cam engine
DOHC
means Double Overhead Cam, or sometimes it could be called "Twin Cam".
A DOHC setup is
used in most of newer cars.
Since it's possible to install multiple
valves per cylinder and place intake valves on the opposite side from
exhaust vales,
a DOHC engine can "breathe" better, meaning that it can
produce more horsepower with smaller engine volume.
Compare:
The 3.5-liter V6 DOHC engine of 2003 Nissan Pathfinder has 240
hp, similar to 245 hp 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.
Pros: High efficiency, possible to install multiple valves per cylinder and adopt variable timing.
Cons: More complex and more expensive design.
Ok, so its been a
while since I posted a blog. I apologize for that but
I will try to get back into the habit of blogging more often.
In the last few blog posts we discussed what OHV is, the advantages of OHV (versus an L-head design) and the meaning of OHC and the different types of OHC. Today we are going to tackle the question of "What is the differences between OHC and OHV?"
The answer is pretty basic. OHV means "Over Head Valve" while OHC means "Over Head Camshaft". Now, OHC is always OHV but OHV is not always OHC. Simply put, OHC engines still have their valves positioned in the cylinder head versus in the block. For a better explanation of what this means, please refer to my previous posts.
Where the difference comes in is where the cam shaft is located. As you can see in the following photo, one of them has a camshaft below the valves and the other has the camshaft above the valves.
In the last few blog posts we discussed what OHV is, the advantages of OHV (versus an L-head design) and the meaning of OHC and the different types of OHC. Today we are going to tackle the question of "What is the differences between OHC and OHV?"
The answer is pretty basic. OHV means "Over Head Valve" while OHC means "Over Head Camshaft". Now, OHC is always OHV but OHV is not always OHC. Simply put, OHC engines still have their valves positioned in the cylinder head versus in the block. For a better explanation of what this means, please refer to my previous posts.
Where the difference comes in is where the cam shaft is located. As you can see in the following photo, one of them has a camshaft below the valves and the other has the camshaft above the valves.
This type of camshaft
typically has a gear that meshes with another gear on the crankshaft.
Though, sometimes it has a "timing chain" to drive the camshaft.
The overhead camshaft (OHC) engine has the camshaft positioned "overhead",
The overhead camshaft (OHC) engine has the camshaft positioned "overhead",
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