DOHC vs. OHV

[Onceler]

I wasn't sure where to post this since its not vw specific, so figured I'd put it in here. So, I work with a Japanese fellow and we're both car guys and tend to talk cars on breaks and such. He looks down on domestic automakers for staying with OHV engines while the Japanese automakers have embraced DOHC engines, claiming they're more high technology.
my only defense is that OHV engines are more compact, but I know there is more to it than that, but don't know how to counter his argument. So, why do domestic manufacturers stick with OHV? And make massive power and good mpg.
The only DOHC engines I've driven were 4 cylinders and slugs at low rpm, but wake up at higher rpm, though annoying to drive in stop and go traffic.
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1972 Karmann Ghia

[TDCTDI]

Tell the little bastard that a DOHC engine is still a OHV engine, the only difference is that the C (camshaft) is also in the cylinder head and that (D) means that there are two of them. The flathead engine design was the one that was not considered OHV, the valves were in the block & the cylinder head was effectively there just to cap off the combustion chamber.
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Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.


GOFUNDYOURSELF, quit asking everyone to do it for you!


An air cooled VW will make you a hoarder.


Do something, anything, to your project every day, and you will eventually complete it.

[Onceler]

[TDCTDI]

Basically, it boils down to where you need to get your power from. Japan & most European countries taxed & limited their vehicles on engine displacement. This meant smaller, lighter cars that relied on horsepower whereas the American cars were larger, heavier & relied more on torque.
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Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.


GOFUNDYOURSELF, quit asking everyone to do it for you!


An air cooled VW will make you a hoarder.


Do something, anything, to your project every day, and you will eventually complete it.

[Q-Dog]

[iowegian]

[mark tucker]

well the missing low end probably has absoultly nothing to do with where the cam is located....just tell him it is what it is.and thats what it is.and yes americans also make plenty of OHC engines. and also DOHC engines.

[Onceler]

Turns out the premise of this post wasn't even correct. Let me explain. He drives a 2017 Dodge Charger AWD with a 3.6liter V6. He claimed it was a pushrod engine and I just took his word for it, but did see that it made almost 300hp so I was pretty impressed.
Well, after googling that engine, I find that it is actually a DOHC engine

So, I think it's safe to say that both of us are stupid
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1972 Karmann Ghia

[scottyrocks]

Can you imagine a Harley Davidson with with overhead cams? Fuggin ugly!!

Oh, waaaait . . .
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“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[Helfen]

OHV and SOHC cams use two valves per cylinder.
DOHC use two cams and use four valves per cylinder, also DOHC engines control their cam timing events depending on the RPM and load on the engine. This is what we call variable valve timing. By controlling intake cams and exhaust cams by retarding and advancing SEPARATLY we can get more torque out of the engine at lower rpm and by changing the events can get more HP at higher RPM. We also can tune the adjustable cams for better mileage. And four valves get more in and more out by volume and faster.

In the 60's some of the cam companies like Isky made mechanical advanced cams for V-8 engines, primarily for the SBC. This gave some low end torque and at high rpm it would advance the cam, problem was it advanced and retarded both the intake and exhaust events at the same time. DOHC is better because #1. 4 valves instead of two, and 2. you can control intake and exhaust valves separately for optimum HP and Torque.

[Onceler]

Even though the premise of this thread turned out to be bs, why,for example, does GM stay with pushrods 2 valve technology, instead of DOHC 4 valve technology with their V8's? And doing quite well with it as far as power and mileage
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1972 Karmann Ghia

[Jon Schmid]

[hotsam]

[TDCTDI]

[Helfen]

[Helfen]

[pondoras box]

Honestly I don't think one is really any better than the other. Just two different ways to get to the same result.

A lot probably has to do with the car design more than engine itself. Smaller imports couldn't cram a big American style engine and fit and would throw the weight bias off something terrible.

With todays cars all being computer controlled you can get the fuel efficiency pretty high on a V8 push rod engine through fuel management and you can get better low end torque on an import style engine through variable valve timing.

Either way smaller engines are turning much bigger HP numbers than they used to and its all through computer control and the evolution of fuel metering.

I think both of you are right in thinking that one engine is better than the other but only 50% of the time. Depends on your application, cost, weight, high end HP or low end torque, rotating mass, and other factors.

My prediction is that GM will have a DOHC engine in the mid-engine Corvette sooner than later. Cost will not really be an issue and using every bit of new technology to gain every advantage in the competitive super car market is paramount to the survival of the brand.

Maybe an automotive engineer can chime in and give us the pros and cons and why one design isn't universally used.
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Looking for anything from Hal Casey Motors out of Hamburg New York, from license plate surrounds to matchbooks.

1961 23 Window (Bobo)
1965 11 Window (Zelda)
1965 13 Window (Lucas)
1957 Oval ragtop
1988 Cabriolet VR6 conversion
Plus a lot of other rusty junk

[hotsam]

I'm not an automotive engineer, but the reasons are something along the lines of:

DOHC:

Pro: More power from a given displacement
Con: Greater Cost/Larger Size/More Complex

Pushrod:

Pro: Less expensive/more power from smaller exterior dimensions/Less Complex
Con: Less power from a given displacement
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1968 Beetle

[Helfen]

[Onceler]