The debate of the camshafts, sohc vs dohc for the valvetrain setup. I may be stating the obvious
here but I must mention that SOHC is the abbreviation for single over head camshaft meaning one camshaft
in an engine head over a set of cylinders and DOHC is the abbreviation for dual over head camshaft meaning
two camshafts in an engine head over a set of cylinders.
Overhead means the camshaft or camshafts is over the cylinders and facilitates the operation
of the four stroke cycle in both
petrol or diesel engines. Camshafts spin at half the the speed of the crankshaft whether it is single
or dual. This is because the crankshaft is required to carry out all four strokes but the camshafts have
to open and close the valves on only two of the four strokes.
So what's the big difference between them and why the debate of sohc vs dohc valvetrains?
Well, because they can have a major difference on the way the engine functions.
The single overhead camshaft setup weighs less resulting in a lighter engine, sohc is also less
complicated than dohc and will require less effort and fewer moving parts to turn one camshaft. An sohc
valvetrain will work well with a simple engine but it will most likely need rocker arms which will add
to the list of moving parts.
The dual overhead camshaft setup provides several benefits as dohc engines are being widely used and
their greater amount of moving parts don't seem to bother engineers. One of the main benefits of dohc is that
it easily incorporates four valves for each cylinder, two intake and two exhaust.
Four valves per cylinder allows an easier flow of fuel and gases both in and out of the cylinder
for the four stroke cycle thereby increasing performance particularly at highs speeds. Another advantage
will be the position of the spark plug or the diesel injector in a dohc engine which will be in the center
of the cylinder allowing a more efficient burning of the air/fuel mixture.
There are sohc engines with 4 valves for each cylinder but the camshaft will also have 4 lobes per
cylinder and the spark plug or diesel injector will not be in the center of the cylinder. DOHC easily
incorporates variable valve timing to further increase performance
but it is not impossible on an sohc engines as Honda is well known to have their variable valve timing V-TEC
on sohc engines, for example the 2006 Honda Legend /Acura RL. So if you're still wondering about sohc vs dohc
they both have their advantages but I would lean towards the dohc.