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OHC, SOHC and DOHC: Which is which?

Hi, Ferman!

Good day. I'd like to ask about the difference between the OHC, SOHC and DOHC engines.

I'm planning to buy a car this year and your explanation will definitely be helpful in my car-buying decision.

Thanks and more power to you and all the staff of Top Gear Philippines!

Boyet

Hi, Boyet!

OHC stands for overhead camshaft. Here, the valves are opened and closed directly by the cam lobes on the camshaft. This is in contrast with the OHV, or overhead valve, configuration where the valves are actuated by pushrods. The OHC configuration allows for lower total mass of the components that drive the valves. OHC configurations also allow for better optimization of cylinder head, intake and exhaust port design compared to OHV engines.

Meanwhile, SOHC stands for single overhead camshaft (per cylinder head), while DOHC means double overhead camshaft (per cylinder head). An SOHC engine will usually be less complex than a DOHC engine albeit, usually, at the cost of slightly less power.

Most modern SOHC and DOHC engines are usually multi-valve engines. DOHC has either three, four or five valves per cylinder while the SOHC has both intake and exhaust valves.

DOHC engines usually optimize one cam for the intake valves and another for the exhaust valves. Sometimes, variable valve cam timing is employed in DOHC engines. This means the opening of the intake valve in relation to the exhaust valve can be varied for those with a single-variable cam mechanism. What happens in these instances is that the cam gear of the cam shaft is attached to a sliding pulley. The sliding pulley allows cam timing and, on certain engines, valve overlap to be varied to allow for better power and efficiency at all engine operating speeds. There are vehicles that have this on both intake and exhaust cams, which allow an even greater degree of adjustability.

I hope that helps clear things up for you and good luck on your car purchase.

Regards,
Ferman Lao
Technical editor

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  • ashek268 Aug 01 2011 @ 01:58pm
     
    Sir Ferman which is more superior when it comes to superior acceleration quarter mile on a stock factory spec engine?
       
  • magnavox Aug 01 2011 @ 02:15pm
     
    hi sir! do we need to adjust/maintenance these parts every PMS? what are the cons?
       
  • envyme Aug 01 2011 @ 04:17pm
     
    pa consuelo de bobo
        1
  • one.edchelle Aug 02 2011 @ 09:12am
     
    nice job ! now i know what engine will i get. thanks Ferman! =)
       
  • krzcuevas Aug 03 2011 @ 11:09am
     
    Hi sir, I'm that that familiar in terms of technicalities. Can you simply give the cons and pros of each. Thank you and more power to you guys!
       
  • krzcuevas Aug 03 2011 @ 11:10am
     
    Hi sir, I'm not that familiar in terms of technicalities. Can you simply give the cons and pros of each. Thank you and more power to you guys!
       
    • walphie Aug 03 2011 @ 01:03pm
       
      DOHC engines usually have a smoother torque curve, but due to their complexity, they're costlier to maintain in the long run, especially if its a high mileage engine. In their earlier days, DOHC engines also had a their peak torque arriving much later, while SOHC, pushrods, and OHC have their peak torque much earlier in the rev range. Nowadays, however, DOHCs can compete in the torque range by using different cam profiles, like what Toyota's VVT-i does.

      In reality, any well designed engine, whether SOHC, OHC, DOHC, or even push rod, should be best for its intended purpose. The Honda B16 is a DOHC design, well-regarded for its performance, while the more modern K18 SOHC found in the FD Civic is known for its efficiency. Chevy has stuck with OHV in its Corvette and Camaro engines. Different principles, different ways of achieving the car/engine's goals. It really depends on the engine designer's priorities when they designed the engine. If you're planning a cam swap or an engine replacement, do your research first.
         
  • Ferman Lao
    Ferman Lao Aug 07 2011 @ 07:52pm
     
    @magnavox,
    It will depend on if the engine has any provision for adjustment of the valves or not.

    @one.edchelle,
    Your welcome.

    @krzcuevas,
    Most DOHC engines will be more powerful than it's SOHC counterpart.
       
  • Juan Camaro 3 months ago
     
    Maaari niyo po bang isalin sa Filipino ang kahulugan ng mga ito at nang lubos na maintindihan naman ng iba nating kababayan? Maraming salamat.
       
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