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Whats the difference between a DOHC and a SOHC motor?

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SOHC stands for Single Overhead Camshaft. That means that there is only one camshaft per header. Inline engines will contain one camshaft. V-type and/or flat will contain 2 camshafts. For a SOHC engine there are usually 2 valves per cylinder but there can be more with the addition of cams for each valve.

DOHC stands for Double Overhead Camshaft. Now there are 2 camshafts per header. So in an inline there are 2 camshafts because there is only one header, but there is 4 in a V-type or flat engine. These DOHC engines usually have 4 valves. One camshaft for the exhaust valves and the other for the intake valves.

Advantages to having a DOHC engine over a SOHC is that the engine has twice as many intake and exhaust valves as a SOHC motor. This makes the engine run cooler and more smoothly, quietly, and efficiently. But the downfall is that DOHC engines cost more for repairs.

More info on SOHC Engines Vs. DOHC Engines

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DOHC- dual over head cam, has 2 cams, one runs the intake valves and the other one runs the exhaust valves. the only disadvantage to dohc is the cost if you ever decide to put bigger cams in, you would have to buy 2 of them

SOHC- single over head cam, one cam has both intake and exhaust lobes on it

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Most, but not all SOHC motors are 2 valve enginges. For example, Honda uses a SOHC head with 4 valves on some of thier machines. Each intake valve is directly actuated by it's own lobe in the cam and the exhuast side uses a two fingered roller rocker arm to actuate the 2 valves on that side. This way you get the benefit of 4 valves per cylinder without all the extra moving parts. Many three valve motors use a two fingered rocker arm to actuate 2 valves off one cam lobe. The only real downside is that it puts more pressure on the cam lobe when it has to lift 2 valves instead of one, which causes the lobe to wear down faster. That is why it is best to use a roller rocker like Honda does to reduce friction.

Edited by DirtDemon
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