Why are most of the AMG engines using SOHC?

[rollakid]

no one in here actually know how the SOHC is choosen for whatover .
but as far as i concern , those engineers are not nut . they know the advantages of DOHC and SOHC , they chose SOHC for reasons . yes , the DOHC is better in terms of technology ... bla bla bla ... but the SOHC too have somethign that DOHC can't archive . and it all depends on what u want , how u refine it , how u engineered it .
not becasue of tech , is becasue of they are choosing what they wanted .
cost cuttng , nah ... who the heck want to cut cost for such big and pricy car . don't tell me rolls royce is cost cutting too ... ferrari cost cutting , those manufactures doesn't need to cut cost on such thing .
investment is very important .

bmw engine more refined than merc . should be conclude that beacsue merc is SOHC so that it cant archive refinement . merc invested more on the car itself while bmw invested more on power , engine , drivability .

mercedes did cut cost since 10 years ago, thats why you view those customer survey thing from europe or USA, mercedes mostly on the bottom third. i dun really know why until i watch top gear, saying mercedes cut cost.

but anyway, we are talking about AMG here, and i dun really think they will cut cost on their top of the range engine (speaking this, merc other than the amg range seems like underpower rubbish -- no offence to merc owner tho, just my 2 cent).

so here's my point of view why merc amg and its DTM car use sohc or 3 valve/cylinder. like what they all have been saying, sohc or 3valve/cylinder is better at low rpm range. moreover, the supercharger they use isn't centrifugal type(at least i think so, dunno mistake or not), thus the power come at low end and lost its effecientcy at high rpm. so why bother make a dohc 4 valve that makes power at high rpm?

AFAIK, their special edition road going verison of their DTM machine redline at 7k rpm, so i think sohc probably already enough.

on the other hand, bmw m series have to rev to something like 7900rpm to reach its peak hp cuz its NA, so surely they need DOHC and 4valves.

just my 2 cent view on this matter tho.. and another way to put it is.... go supercharge all your SOHC proton :D

 

[bridgestoneRE711]

yes , cut cost on manufacturing . but the cost on the investment , research won't be cut down for such big company .

i am talking SOHC and DOHC with Supercharger and Turbo as a comparision . It depends on which one u really want . more power at highend or average more power for all the band .

SOHC and DOHC has its own advantages. no point argueing here . higher REVV the DOHC perform well ,and has higer bhp on higher RPM . but because if u want more torque , u need to tune the DOHC to have more torque on lower rpm ,and still need to sacrifice the power of highend . that is why still need to stick to SOHC for some reason . but there any tons of reasons that we still don't know and we need a pro to explain this .

 

[rollakid]

but there's one thing i want to talk about is the number of cams you have and the number of valves you have. they seems to be different topic.

for what i know so far, sohc deals with both intake and exhaust valve with the same cam and use rocker arm to move them. advantage is simple and weight less and the head can be smaller. however, with the rocker arm and stuff, it produce more friction, thus not good on high revs.

dohc on the other hand have less friction, thus able to spin faster. they produce more power probably because they can tune different timing for intake and exhaust, instead of just retard or advance in the sohc. which makes dohc better at high rev (?)

and about the sohc have lower end power and dohc have higher end power, i personaly think (without any profesional knowledge, just some common sense and simple automotive information) that it depends more on the number of valves. with a lower profile and duration cam for normal car use, your engine cant rev high. and because of that, having a 4valve/cylinder head would be a disadvantage because engien power depends very much on velocity of air rushing into the engine. with 2 intake port, the air velocity will be lower, thus lower power. this also makes 3valve better than 4 valve at low rpm, and this is also the reason why toyota use TVIS to close 1 valve so the air can rush in faster through the other valve.

at high rev, single intake port isn't enough for all the air to come in thus having 2 port for intake helps alot. thus multi valve engine head is better for higher revs.

but then, there's alot of things i'm not clear yet. i heard honda's D16B runs 16valve sohc, dunno true or not. and on top of that, toyota's old 2TG engine runs 8valve, yet DOHC.

i really hope some more experienced sifu can continue where i can't explain. i think this is worth discuss at least.

 

[boggysv]

I would guess it's for a quicker engine warm up while being able to not run it too hot.

Emissions...all about the emissions

 

[nasscmw]

AMG uses SOHC for the V8 because Mercedes supplied them that way. Only the V12s are DOHC. If am I not mistaken the in line engines are DOHC as well.

The reason why Mercedes did this was because they wanted to cut cost. THe V8 DOHCs were way better. Their SOHC engines are the older tech engines so from the newer engines they switched back to the older engines. I think this happened when Daimler bought MErcedes. It seems as those that's the better. AMG has to supercharge the engine because they can't beat Audi's new RS4 4.3 litre 400 over hp or the BMWs V10. Those are damn good engines and NA.

 

[zan]

but there's one thing i want to talk about is the number of cams you have and the number of valves you have. they seems to be different topic.

but then, there's alot of things i'm not clear yet. i heard honda's D16B runs 16valve sohc, dunno true or not. and on top of that, toyota's old 2TG engine runs 8valve, yet DOHC.

i really hope some more experienced sifu can continue where i can't explain. i think this is worth discuss at least.

old fiats and alfas from the 60s were already running DOHC but only 2 valves per cylinder.

honda does produce 16 valve engines with SOHC, D16B is one example.

others like 4G92P on wira 1.6 is 16V SOHC as well as waja's previous 4G18P.

 

[si|verfish]

Here's something I ripped off PaulTan.org.

SOHC vs DOHC Valvetrains

June 22, 2005 at 5:39 pm · Filed under Cars, Howtos

Plenty of people have been talking about how the Savvy only has an SOHC engine so it is inferior, and old technology. So I decided to post this entry so that people will be better informed on what SOHC or DOHC really is.

SOHC and DOHC are basically two different ways to configure the valvetrain. In the whole valve train setup there are camshafts, lifters, rockers, valves and springs. It is best that the valvetrain is light. Valves open at intervals of 25 times a second at 3000rpm. If the valvetrain is heavy, when the camshaft lifts it the valvetrain will just keep going up until the valve spring catches it. This is called valve float. You can overcome this with stronger (which means heavier) springs, but this extra weight increases the power requirements to open the valve.

The cams are driven by the crankshaft, using either a belt or chain called a timing belt or timing chain. If the timing belt/chain snaps and the camshaft stops spinning, the piston coming back up the combustion chamber might hit the open valves. This is very costly. That’s why you should always change your timing belt/chain at the interval specified by your car manufacturer.

SOHC refers to Single Overhead Camshaft. In the days before DOHC, it was known as OHC, with no need to differentiate between a single or double camshaft. In SOHC, the camshaft is situated in the cylinder head, above the valves. The valves are opened and closed either directly with a shim between the cam lobe and the valve stem, or via a rocker arm. SOHC engine valve configurations typically have 2 or 3 valves per cylinder. It is also possible to have 4 valves per cylinder using SOHC but this translates into a complicated combination of rocker arms and cam lobe shapes. An example would be the 4G92P in my car which is a SOHC but has 4 valves per cylinder.

DOHC refers to Double Overhead Camshaft. This arrangement uses two camshafts in each cylinder head. Two cams per cylinder head means that a DOHC V engine has 4 camshafts because it has 2 banks of cylinder heads. This allows the manufacturer to easily implement a 4 valve per cylinder setup. Most of the time it also allows the engine to rev higher. It also allows better placement of the valves in an optimized setup that gives you maximum performance. But the disadvantage of such a setup is more weight, more cost and more complexity. It takes more stuff to drive two camshafts. The main reason to use DOHC is to drive more valves per cylinder. If a SOHC setup can allow 4 valves per cylinder, having a DOHC engine will not bring that much benefits over SOHC and the additional weight becomes a burden instead. DOHC engines also allows the spark plug to be placed right in the middle of the combustion chamber. This promotes efficient combustion. With SOHC, the camshaft is usually in the middle of the head because it has to drive both the intake and exhaust valves, robbing the sparkplug of it’s optimal location.

In the end, a SOHC 16 valve engine would have better torque on the low end where the DOHC valvetrain’s weight results in lower torque. But at high engine speeds, the 16 valve DOHC engine’s peak torque and horsepower would be greater. That’s the trade-off. With the amount of valves being equal, SOHC has better low-end torque because the valvetrain package is lighter while DOHC has better top-end power.

Other benefits of DOHC would be making it easier to implement variable valve timing technologies (which I will cover in another blog post) and also you can tweak it better with adjustable cam pulleys. If you were to put high-profile cams in your DOHC engine, the cam lobe profile can also be more optimized than a SOHC engine because you can play around with the lobe shape easier with separate camshafts for the intake and exhaust valves.

Why more valves per cylinder? Why not just make 1 huge intake valve and 1 huge exhaust valve? Bigger valves weigh more than the smaller one, so controlling the extra weight as it gets flung open and close becomes difficult. The spring has to be stiffer. A stiffer spring means more energy has to be spent overcoming the valve pressure. This partially oversets the gains which a bigger valve has to offer. Another problem with a single big valve is at lower RPMs the intake velocity will be lower. I’m sure you guys know this… the same amount of air going through a big pipe will have lower pressure than the same air going through a smaller opening. Think of how you can control the water pressure of your garden hose by adjusting the opening size with your finger. Because of the velocity drop, low RPM torque and driveability will suffer. Although two smaller valves weigh the same as 1 big valve, and with the extra rocker arms and springs they can actually end up weighing more, this is offset by less mass to be overcome when opening and closing the valves.

So, are more valves per cylinder really that beneficial? Here’s comparing a Nissan VG30E to a VG30DE. Both are 3 liter electronic fuel injection engines, but one is a SOHC with 2 valves per cylinder and the other is DOHC with 4 valves per cylinder.

We can see that torque at low RPMs are about the same for both engines, but at higher speeds the 2-valve per cylinder engine has reached it’s peak and has to switch to the next gear while the twincam 4 valve per cylinder engine continues making more power at the top-end of the powerband. The powerband is also longer. (Note: I’ve added this graph here to show you the difference between 2-valve and 4-valves, not SOHC vs DOHC. Couldn’t find any graphs for SOHC vs DOHC. Sorry!)

So to sum it all up, SOHC has better low-end power, DOHC has better high-end power and overall maximum power. 4 valves per cylinder is much better than 2 valves per cylinder and it doesn’t matter whether 4-valves is achieved via SOHC or DOHC.

Source: http://paultan.org/archives/2005/06/22/sohc-vs-dohc-valvetrains/

 

[netmatrix]

I think RELIABILITY is the main agenda here. Not power. If you look at it another way, 4 valves per cylinder, you have smaller valves and smaller metal that surrounds the valve. But with 2 or 3 valves, you have more metal that surrounds the valves. Do take into consideration on mechanical stress, friction and complexity of engine design if you use more valves. Not to mention cost savings.:regular_smile:

If a SOHC engne can make similar power to a DOHC engine, so whats the fuss all about? For car freaks, low end and top end power is the debating point. But to a person who has moolah to buy a 600hp car. Would you think he care if it was DOHC ot SOHC?:shades_smile:

 

[si|verfish]

AMG has recently designed their OWN V8 engine. A 6.3 litre V8 which revs to 7200rpm and puts out 510 bhp. And of course, it's NA and its got all the usual tech stuff that goes with high revving NA engines. They've stuck it in the new Mercedes R class which has just been launched.

You maybe thinking at this point that, "Hey, it's bigger than the M5's 5.0 litre V10 and generates less power for its size...". and you've got a fair point. BUT, and its a big but, I'm not sure my facts and figures are correct, apparently the AMG V8 is a very compact and light engine. And although its got huge displacement, its actually lighter than the BMW V10. Thus a better power to weight ratio. Thanks largely to its all aluminium construction. The BMW V10 needed a very strong crankcase and therefore more weight. The AMG V8 has also got more torque, thanks to its size.

I'd like to see one in supercharged of twin turbo form. Put that in an SLK and let fly.

 

[ORE GANAH]

ore kato ambik enjin doch la!...jange soch,kuat pun kuat,nak memotong pun yakin,...sapo kato soch kuat tu penipu belako...pijak atah bumi gak...gilosssssssss

 

[coterie30]

even all porsches r runnin SOHC boxers.. ;)

 

[zan]

ore kato ambik enjin doch la!...jange soch,kuat pun kuat,nak memotong pun yakin,...sapo kato soch kuat tu penipu belako...pijak atah bumi gak...gilosssssssss

SP4H campro 1.6 guna DOHC mmg lagi kuat dari 4G18P 1.6 SOHC. 110PS vs 103PS.

tp 4G92P 1.6 SOHC lagi kuat dari SP4H campro 1.6. 116PS vs 110PS.

guano lagu tuh?

 

[darahhitam]

OMG, zan, now this suddenly turns to be sohc-dohc forum in a Kelantanese-lingual eh?

lol.

Ore Ganah (humbly translated to be Brutal Man) - that's not the right way to bash SOHC engine or whatever, could you read the earlier (valuable) posts before "commenting"?


Cheers.

 

[Nieto]

even vios and city use sohc~!! but i think DOHC has higher response