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Onceler Samba Member
Joined: May 28, 2010 Posts: 1647 Location: Indiana
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Posted: Sun Aug 12, 2018 8:16 pm Post subject: DOHC vs. OHV |
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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. _________________ 1972 Karmann Ghia |
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TDCTDI Samba Advocatus Diaboli
Joined: August 31, 2013 Posts: 12858 Location: North Carolina
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Posted: Sun Aug 12, 2018 8:34 pm Post subject: Re: DOHC vs. OHV |
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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. _________________ 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.
Last edited by TDCTDI on Sun Aug 12, 2018 8:43 pm; edited 1 time in total |
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Onceler Samba Member
Joined: May 28, 2010 Posts: 1647 Location: Indiana
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Posted: Sun Aug 12, 2018 8:40 pm Post subject: Re: DOHC vs. OHV |
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TDCTDI wrote: |
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. |
Ha, yeah ur right, maybe i should clarify...i mean pushrod engines. I just need some good arguments to let him know us Americans ain’t stupid _________________ 1972 Karmann Ghia |
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TDCTDI Samba Advocatus Diaboli
Joined: August 31, 2013 Posts: 12858 Location: North Carolina
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Posted: Sun Aug 12, 2018 9:26 pm Post subject: Re: DOHC vs. OHV |
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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. _________________ 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. |
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Q-Dog Samba Member
Joined: April 05, 2010 Posts: 8700 Location: Sunset, Louisiana
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Posted: Mon Aug 13, 2018 8:58 am Post subject: Re: DOHC vs. OHV |
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Onceler wrote: |
TDCTDI wrote: |
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. |
Ha, yeah ur right, maybe i should clarify...i mean pushrod engines. I just need some good arguments to let him know us Americans ain’t stupid |
Each have advantages and disadvantages. But, he's still right ... Americans are stupid. _________________ Brian
'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle |
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iowegian Samba Curmudgeon
Joined: February 16, 2005 Posts: 9829 Location: Somewhere between Dubuque and Keokuk
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Posted: Mon Aug 13, 2018 10:32 am Post subject: Re: DOHC vs. OHV |
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Q-Dog wrote: |
Onceler wrote: |
TDCTDI wrote: |
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. |
Ha, yeah ur right, maybe i should clarify...i mean pushrod engines. I just need some good arguments to let him know us Americans ain’t stupid |
Each have advantages and disadvantages. But, he's still right ... Americans are stupid. |
Now don't go gettin' all political on us. |
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mark tucker Samba Member
Joined: April 08, 2009 Posts: 23937 Location: SHALIMAR ,FLORIDA
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Posted: Mon Aug 13, 2018 10:45 am Post subject: Re: DOHC vs. OHV |
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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. |
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Onceler Samba Member
Joined: May 28, 2010 Posts: 1647 Location: Indiana
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Posted: Mon Aug 13, 2018 11:54 am Post subject: Re: DOHC vs. OHV |
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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 _________________ 1972 Karmann Ghia |
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scottyrocks Samba Member
Joined: August 19, 2016 Posts: 2666 Location: Long Island, NY
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Posted: Mon Aug 13, 2018 3:40 pm Post subject: Re: DOHC vs. OHV |
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Can you imagine a Harley Davidson with with overhead cams? Fuggin ugly!!
Oh, waaaait . . . _________________ “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' |
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Helfen Samba Member
Joined: January 19, 2009 Posts: 3450 Location: Vulcania
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Posted: Mon Aug 13, 2018 4:36 pm Post subject: Re: DOHC vs. OHV |
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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. |
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Onceler Samba Member
Joined: May 28, 2010 Posts: 1647 Location: Indiana
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Posted: Mon Aug 13, 2018 5:05 pm Post subject: Re: DOHC vs. OHV |
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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 _________________ 1972 Karmann Ghia |
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Jon Schmid Samba Member
Joined: May 29, 2012 Posts: 2038 Location: Southern California
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Posted: Mon Aug 13, 2018 7:32 pm Post subject: Re: DOHC vs. OHV |
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Helfen wrote: |
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. |
And who came up with the variocam concept? Hmmm... |
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hotsam Samba Member
Joined: December 02, 2015 Posts: 366 Location: Ashburn, VA
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Posted: Tue Aug 14, 2018 7:35 am Post subject: Re: DOHC vs. OHV |
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Onceler wrote: |
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 |
Pushrod engines tend to be more compact. _________________ 1968 Beetle |
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TDCTDI Samba Advocatus Diaboli
Joined: August 31, 2013 Posts: 12858 Location: North Carolina
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Posted: Tue Aug 14, 2018 7:59 am Post subject: Re: DOHC vs. OHV |
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Helfen wrote: |
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. |
There are always exceptions to the rules. VW had the "DOHC" VR6 that was 2 valves per cylinder but they got away with labeling it DOHC because there were two cams in the same cylinder head, One for the front bank & one for the rear bank.
VW also had the 20 valve engines which had 3 intake & 2 exhaust.
hotsam wrote: |
Pushrod engines tend to be more compact. |
Which brings us back to the VR6 which was a 15* V6 "DOHC" that took up the same space as a 4 cylinder. _________________ 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. |
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Helfen Samba Member
Joined: January 19, 2009 Posts: 3450 Location: Vulcania
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Posted: Tue Aug 14, 2018 8:15 am Post subject: Re: DOHC vs. OHV |
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Onceler wrote: |
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 |
Cheaper, less complicated, easier to produce. Tradeoff, less efficiency=HP & Torque. |
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Helfen Samba Member
Joined: January 19, 2009 Posts: 3450 Location: Vulcania
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Posted: Tue Aug 14, 2018 8:29 am Post subject: Re: DOHC vs. OHV |
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hotsam wrote: |
Onceler wrote: |
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 |
Pushrod engines tend to be more compact. |
GM built other engines like Pontiac's SOHC 6 from 1966-1969 or 1971-1977 Chevrolet 2300 SOHC 4.
When in January 1963 GM's self imposed ban on racing Pontiac had three OHC engines getting ready for production. The only engine that finally came out of advanced engineering was the 1966-69 OHC six.
If the ban hadn't gone into effect Chrysler's Hemi would have been fodder for the 421 DOHC 4 valve per cylinder Pontiac was going to produce for production. Even nearer to production was the 421 SOHC ( which used some of the same tooling and parts from the OHC Pontiac six) producing 650 HP on a four barrel carb. and this was 1963. |
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pondoras box Samba Member
Joined: March 22, 2004 Posts: 1226 Location: Eerie PA
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Posted: Tue Aug 14, 2018 8:48 am Post subject: Re: DOHC vs. OHV |
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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. _________________ 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 |
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hotsam Samba Member
Joined: December 02, 2015 Posts: 366 Location: Ashburn, VA
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Posted: Tue Aug 14, 2018 9:31 am Post subject: Re: DOHC vs. OHV |
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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 _________________ 1968 Beetle |
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Helfen Samba Member
Joined: January 19, 2009 Posts: 3450 Location: Vulcania
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Posted: Tue Aug 14, 2018 11:15 am Post subject: Re: DOHC vs. OHV |
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pondoras box wrote: |
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. |
From a engineering point of view four valves per cylinder are more efficient. The more fuel mixture you can get in and exhaust out is just plain physics. Adjusting valve timing and separately ( VVT ) between intake cam and exhaust cam increase horsepower, torque, efficiency and lower emissions.
Engines with a single camshaft controlling intake and exhaust events are designed as a compromise between HP, Torque, emissions, efficiency. |
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Onceler Samba Member
Joined: May 28, 2010 Posts: 1647 Location: Indiana
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Posted: Tue Aug 14, 2018 8:59 pm Post subject: Re: DOHC vs. OHV |
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Helfen wrote: |
pondoras box wrote: |
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. |
From a engineering point of view four valves per cylinder are more efficient. The more fuel mixture you can get in and exhaust out is just plain physics. Adjusting valve timing and separately ( VVT ) between intake cam and exhaust cam increase horsepower, torque, efficiency and lower emissions.
Engines with a single camshaft controlling intake and exhaust events are designed as a compromise between HP, Torque, emissions, efficiency. |
I think the long view win goes to America if you look at hp, torque, and mpg, with the least amount of cost and complexity. they had a good run when there wasn't any competition and the yen was cheap. Competition in the first world ain't so easy _________________ 1972 Karmann Ghia |
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