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Helfen
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Joined: January 19, 2009
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Location: Vulcania
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 Posted: Tue Aug 14, 2018 9:26 pm Post subject: Re: DOHC vs. OHV |
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| Onceler wrote: |
| 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 |
Define what America is winning? |
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Onceler
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Joined: May 28, 2010
Posts: 1646
Location: Indiana
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| Posted: Tue Aug 14, 2018 9:36 pm Post subject: Re: DOHC vs. OHV |
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| Helfen wrote: |
| Onceler wrote: |
| 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 |
Define what America is winning? |
My dollars
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ach60 
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Posts: 4139
Location: Santa Maria
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| Posted: Wed Aug 15, 2018 1:23 am Post subject: Re: DOHC vs. OHV |
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| TDCTDI wrote: |
| 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. |
Blame Henry Ford, and the Model T
To keep the Model T out of their countries, protecting their domestic Auto Industries European Countries adopted a tax and licensing strategy based on engine displacement.
The Model T has a 177ci or 2.9 litre engine, that's big for a 4 cylinder.
Which is better? DOHC or SOHC or Cam in Block, all you have to do is look at Porsche engine development.
For Porsche turns out DOHC, water cooled was the best.
Engines utilize 4 valves for better breathing, That's the way it is. the simplest way to run 4 valves is with 2 cams.
But Porsche did it the hard way first.
Which is better? DOHC or SOHC or Cam in Block, all you have to do is look at Corvette engine development.
For Chevy turns out Cam in Block, water cooled was the best.
Because they could control development costs, and spread them out over a wide range of vehicles including trucks,
which is where most V8s have ended up since the 90's
Which is better? DOHC or SOHC or Cam in Block, all you have to do is look at Toyota engine development.
For Toyota turns out SOHC, water cooled was the best.
Because they could dump a shit load of machined parts for a rubber band.
Nothing explains the VW EA88 
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TDCTDI
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| Posted: Wed Aug 15, 2018 4:34 am Post subject: Re: DOHC vs. OHV |
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| ach60 wrote: |
Nothing explains the VW EA88
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That someone deep inside the engineering department of VW had a backup plan for total failure of the company if dieselgate didn’t.
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Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.
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Helfen
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Joined: January 19, 2009
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Location: Vulcania
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| Posted: Wed Aug 15, 2018 8:08 am Post subject: Re: DOHC vs. OHV |
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[quote="ach60"]
| TDCTDI wrote: |
| 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. |
Blame Henry Ford, and the Model T????????????????????????????
To keep the Model T out of their countries, protecting their domestic Auto Industries European Countries adopted a tax and licensing strategy based on engine displacement.
The Model T has a 177ci or 2.9 litre engine, that's big for a 4 cylinder.
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In 1920 the German government had imposed a tariff so high that it amounted to a prohibition against importing foreign automobiles. Ford had anticipated this and began manufacturing model T's in 1925 in Germany until the Beginnging of the new car the model "A" in 1927. Ford produced cars and trucks from the 20's thru the war and to this day along with G.M.
G.M. bought Opel in 1929 to achieve the same results. G.M. also bought the English Vauxhall in 1925.
So, the tariff THREAT worked to get Ford and G.M. firmly into their countries by the middle and end of the 1920's.
Here in the U.S. during the Carter administration the U.S. Threatened tariffs against European and Japanese cars. This forced the Germans and the Japanese to build plants and invest in this country. A good thing for the U.S.A. Now some of those companies have more U.S. made content than the so called domestics.
Does this strategy sound familiar? and it can be used both ways. It can be used to help a industry be competitive in the world market when another nation undervalues it's currency or products to undercut your competitiveness. The idea is to threaten to level the playing field.
NOW back to engines please. |
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ach60
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| Posted: Wed Aug 15, 2018 5:01 pm Post subject: Re: DOHC vs. OHV |
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| Helfen wrote: |
NOW back to engines please. |
Lighten up Francis
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Onceler
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Posts: 1646
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| Posted: Wed Aug 15, 2018 5:39 pm Post subject: Re: DOHC vs. OHV |
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So, I have to ask, why would pushrod V8's be better for trucks in GM's case. or are they?
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TDCTDI
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| Posted: Wed Aug 15, 2018 6:15 pm Post subject: Re: DOHC vs. OHV |
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TORQUE! Large displacement, longer stroke equals lots of bottom end grunt. Pushrod engine equals simplicity of sorts & two smaller valves per cylinder gives an inherent rev limiter of sorts. When you’re trying to use a truck for it’s intended purpose like pulling a trailer or hauling a camper you need bottom end power. Before every other Soccer mom or day trader had a $80,000, forced induction 4WD diesel dually, trucks had simple, low horsepower, torquey 350/400/454ci V8 engines.
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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.
Last edited by TDCTDI on Thu Aug 16, 2018 5:45 am; edited 1 time in total |
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Onceler
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| Posted: Wed Aug 15, 2018 6:41 pm Post subject: Re: DOHC vs. OHV |
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I like torque. But it just seems that in a market as lucrative is trucks, GM wouldn't risk loosing out to the competition if they could develope a DOHC 4 valve truck engine with vvt to have both torque and HP for trucks. I don't know jack about engine performance ( I just copy what others do). Is there something inherent in a 2 valve chamber vs. a 4 valve chamber that would steer developed in one direction or the other?
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Helfen
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| Posted: Wed Aug 15, 2018 8:39 pm Post subject: Re: DOHC vs. OHV |
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Lets look at two V-8 engines in trucks today ( not 350, 400, 396, 402, 427, or 454).
Two engines of close displacement of each other for 2018.
G.M. Powertrain's 5.3 V-8. OHV pushrod V-8, two valve per cylinder. Fuel injection
355 H.P. & 383 Lbs. Ft. of Torque.
Nissan 5.6 V-8. DOHC, 4 valves per cylinder, variable valve timing, Compound angle Hemi head, fuel injection.
390 H.P. & 394 Lbs. Ft. of Torque. |
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Onceler
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| Posted: Thu Aug 16, 2018 8:11 am Post subject: Re: DOHC vs. OHV |
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| Helfen wrote: |
Lets look at two V-8 engines in trucks today ( not 350, 400, 396, 402, 427, or 454).
Two engines of close displacement of each other for 2018.
G.M. Powertrain's 5.3 V-8. OHV pushrod V-8, two valve per cylinder. Fuel injection
355 H.P. & 383 Lbs. Ft. of Torque.
Nissan 5.6 V-8. DOHC, 4 valves per cylinder, variable valve timing, Compound angle Hemi head, fuel injection.
390 H.P. & 394 Lbs. Ft. of Torque. |
Wow, looks like GM's 5.3 is lacking compared to this Nissan 5.6 in performance.
Now, compare the Ram 5.7L Hemi- pushrod V8. It makes 405hp and 410 lb-ft.
There just doesn't seem to be a correlation of 4-valves being worth all the extra size and complexity.
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TDCTDI
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| Posted: Thu Aug 16, 2018 8:29 am Post subject: Re: DOHC vs. OHV |
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Realistically, unless you're hauling or towing, anything over 70hp is a waste. It only takes about 15 HP to maintain 65MPH, anything more is all about how fast you can get it there & how much faster it will go over 65MPH.
_________________
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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TDCTDI
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Joined: August 31, 2013
Posts: 12850
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| Posted: Thu Aug 16, 2018 8:33 am Post subject: Re: DOHC vs. OHV |
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| Onceler wrote: |
There just doesn't seem to be a correlation of 4-valves being worth all the extra size and complexity. |
Internal combustion engines have a very limited "sweet spot" where they make peak horse power & torque. Variable valve timing increases the "sweet spot".
_________________
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: Thu Aug 16, 2018 9:40 am Post subject: Re: DOHC vs. OHV |
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| TDCTDI wrote: |
| Onceler wrote: |
There just doesn't seem to be a correlation of 4-valves being worth all the extra size and complexity. |
Internal combustion engines have a very limited "sweet spot" where they make peak horse power & torque. Variable valve timing increases the "sweet spot". |
Correct, instead of looking at peak HP and Torque you need to look at the overall HP and Torque figures in a engines whole useable rpm range. You don't normally see that in advertising.
Last edited by Helfen on Thu Aug 16, 2018 10:20 am; edited 1 time in total |
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Helfen
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| Posted: Thu Aug 16, 2018 10:03 am Post subject: Re: DOHC vs. OHV |
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| Onceler wrote: |
| Helfen wrote: |
Lets look at two V-8 engines in trucks today ( not 350, 400, 396, 402, 427, or 454).
Two engines of close displacement of each other for 2018.
G.M. Powertrain's 5.3 V-8. OHV pushrod V-8, two valve per cylinder. Fuel injection
355 H.P. & 383 Lbs. Ft. of Torque.
Nissan 5.6 V-8. DOHC, 4 valves per cylinder, variable valve timing, Compound angle Hemi head, fuel injection.
390 H.P. & 394 Lbs. Ft. of Torque. |
Wow, looks like GM's 5.3 is lacking compared to this Nissan 5.6 in performance.
Now, compare the Ram 5.7L Hemi- pushrod V8. It makes 405hp and 410 lb-ft.
There just doesn't seem to be a correlation of 4-valves being worth all the extra size and complexity. |
Consider this and try to put this into perspective. In 1963 you could buy a new 1963 Pontiac Catalina with a 320 HP 421cu.inch engine. You could also buy that car with a 410 H.P. 421 cu.inch engine. What is the difference? Camshaft, Compression, Valve size, carburetion, factory exhaust headers. In Super Stock that 410 HP car which weighed 3600 lbs. was making the quarter mile trip in the high 11's at 120-126mph. If you do the math those Pontiac's engines were grossly underrated. The truth was the factory had underrated the HP figures. Stock out of the box with fine tuning they were making 550 + hp. Why did they underrate the figures? Anti racing elements in the government who questioned why G.M. was building such fast cars. Remember this is the Ralph Nader era.
If you make all things equal. Displacement, induction, exhaust, compression. a four valve wins over two. Add in variable timing and the four valve really pulls away. It's plain physics and math. |
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Mal evolent
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| Posted: Thu Aug 16, 2018 12:42 pm Post subject: Re: DOHC vs. OHV |
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if you rev it up like a Dremel tool, you need overhead cams. I consider Dremels expendable.
if you prefer to get power via torque, run a stroker at a realistic speed, and run a 6 speed transmission.
compare the number of old Japanese bikes versus old Harleys on the road and decide for yourself who is stupid.
go to the airport and see how many commercially made aircraft have overhead cams
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Onceler
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| Posted: Thu Aug 16, 2018 9:11 pm Post subject: Re: DOHC vs. OHV |
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Don't get me wrong, I'm all for new technology as well as appreciating the old. I just find it odd that in 2018, 4 valve engines aren't ubiquitous by now, that's why I'm questioning. Too be honest I would prefer to travel to work in a automated drone aircraft, would cut commute time and I could sleep on the way, lol
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mark tucker
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| Posted: Fri Aug 17, 2018 12:50 am Post subject: Re: DOHC vs. OHV |
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| we see whoo is wine~ing |
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Helfen
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Posts: 3450
Location: Vulcania
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| Posted: Fri Aug 17, 2018 8:51 am Post subject: Re: DOHC vs. OHV |
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| Onceler wrote: |
| Don't get me wrong, I'm all for new technology as well as appreciating the old. I just find it odd that in 2018, 4 valve engines aren't ubiquitous by now, that's why I'm questioning. Too be honest I would prefer to travel to work in a automated drone aircraft, would cut commute time and I could sleep on the way, lol |
[I just find it odd that in 2018, 4 valve engines aren't ubiquitous by now.]
I was just looking at 2018 NISSAN model line. Every single car model or truck model has DOHC four valves per cylinder and VVT. With Nissan, this trend was started over 20 years ago. |
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Onceler
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| Posted: Fri Aug 17, 2018 6:02 pm Post subject: Re: DOHC vs. OHV |
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| Helfen wrote: |
| Onceler wrote: |
| Don't get me wrong, I'm all for new technology as well as appreciating the old. I just find it odd that in 2018, 4 valve engines aren't ubiquitous by now, that's why I'm questioning. Too be honest I would prefer to travel to work in a automated drone aircraft, would cut commute time and I could sleep on the way, lol |
[I just find it odd that in 2018, 4 valve engines aren't ubiquitous by now.]
I was just looking at 2018 NISSAN model line. Every single car model or truck model has DOHC four valves per cylinder and VVT. With Nissan, this trend was started over 20 years ago. |
VVT is also applied to pushrods 2 valve engines, for example the ram 5.7 hemi mentioned above. Japanese usually are very mindful of material, cost/pc., and physical size usage, however in this case it's the total opposite. 2x the cams, 2x the valves, more physical size. then again, as mentioned gov't. Intervention can have strange effects
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