I noticed that Acura still uses SOHC engine on some of their cars. Is there a specific reason why? I've personally talked to an Acura technician about this question but he just said it allows better flow. Not sure what he meant by that?
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Welcome to Motor Vehicle Maintenance & Repair!– Pᴀᴜʟsᴛᴇʀ2 ♦Jul 2, 2018 at 18:46
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GM still uses cam-in-block for some seriously high-power engines. (eg, the Corvette.) SOHC isn't necessarily better, nor is DOHC necessarily better than SOHC. And, it adds significant to the design, construction and maintenance of the engine. It depends on the application and the design & budget constraints. (OHC engines are also a lot taller than cam-in-block, which can be an issue.)– 3DaveJul 2, 2018 at 20:40
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@3Dave ohc engines may not be taller - it can also depend on the bore v stroke - older engines had a longer stroke with a consequent slower max rpm compared to oversquare designs which leads to a higher revving engine...– Solar MikeJul 2, 2018 at 22:32
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A manufacturer may also decide to continue using designs and manufacturing tooling that have already been paid for.– DavidRecallsMonicaJul 3, 2018 at 18:49
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1 Answer
The big question back at you here is why shouldn't they use SOHC engines? The biggest reason to use them is because DOHC engines are more expensive to produce (which price would get pushed back onto the consumer), there are more moving parts in them (which means they will fail sooner), and they can still do VTEC in either version.
There are other reasons, as well. A SOHC engine is lighter than a DOHC engine because it takes more material in the head to support the DOHC design. The SOHC is also more compact, which leaves more room for design concerns in the engine compartment. This may help supplement hood clearances which can lead to better frontal area of the vehicle, leading to better fuel economy on the road.
The going theory is you can make more power and have better control over the DOHC engine for performance applications, however, if you're talking about basic, right off the showroom floor applications, there's no need to make things more complicated with a DOHC design when you can make the same power/torque with a SOHC design with less cost.
answered Jul 2, 2018 at 19:02
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Thank you for your clear answer. I simply thought SOHC is less sophisticated. Thanks again!– user38723Jul 2, 2018 at 19:15
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I agree, and in many engines were there were both 8v and 16v versions, the 8v versions were mostly indestructible while the 16v's were troublesome and didn't offer much more power, and only so in the higher rpm range.– BartJul 2, 2018 at 21:37
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An additional comment about DOHC and SOHC performance: Usually SOHC has better flow in the cylinder head at low engine RPM, leading to a bit more torque. The advantages of DOHC (better maximum flow) only really show at high RPM and are more suitable for sportscars. Thats also why DOHC was labeled as such in the 80's and early 90's.– MadMarkyJul 3, 2018 at 9:08
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@MadMarky - I've seen what you're saying whispered around the internet, but wonder the validity of it. The reason I say this is, both the SOHC and DOHC setups can have 4-valve/cyl. You could make them exactly the same in every other way. Both will flow the same amount of air at any given RPM range. If so, they'll have the same HP/TQ #'s at any given RPM. I think your statement stems from the thought that SOHC setups only have 2-valve/cyl ... if so, then it would be true.– Pᴀᴜʟsᴛᴇʀ2 ♦Jul 3, 2018 at 12:59
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@Pᴀᴜʟsᴛᴇʀ2 a 2-valve head generally has less total port diameter than a 4-valve head. This leads to a higher intake air velocity and better flow at low RPM. At higher RPMs the restricted flow will limit the power delivery. Variable valve timing/valve lift systems have largely negated the 'slow flow' issues of 4-valve heads at low RPM.– MadMarkyJul 3, 2018 at 13:51