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ekzos_pipe
05-07-05, 08:14 PM
Kita bila cakap pasal overhead cam je mesti org kata Double semestinya lagi baik dari Single 100% tanpa mengambil kira apa yg berlaku disebalik valve, tarpet, cam, timing belt/chain bla bla bla...

nah pasal SOHC vs DOHC - setiap satu ada kelebihan



SOHC vs DOHC Valvetrains

posted on 22/6/2005 by Paul Tan in 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. Thatís 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 itís optimal location.

In the end, a SOHC 16 valve engine would have better torque on the low end where the DOHC valvetrainís weight results in lower torque. But at high engine speeds, the 16 valve DOHC engineís peak torque and horsepower would be greater. Thatís 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. Iím sure you guys know thisÖ 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? Hereís 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.

http://paultan.org/wp-content/sohcvsdohchp.gif
http://paultan.org/wp-content/sohcvsdohctq.gif

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 itís 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.

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 doesnít matter whether 4-valves is achieved via SOHC or DOHC.


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

FunctionX
05-07-05, 09:16 PM
orang secara automatik anggap yg DOHC superior sebab kalau DOHC konpem lagi banyak valve... dan secara am more valves = more power...

tapi pada pendapat aku lah... beza DOHC ngan SOHC ni cuma ketara kat trek. Kalau tak main racing (atau rempit), rasanya kalau orang tak perasan pun...

gogsard
06-07-05, 08:06 AM
tapi pada pendapat aku lah... beza DOHC ngan SOHC ni cuma ketara kat trek. Kalau tak main racing (atau rempit), rasanya kalau orang tak perasan pun...

mengikut penerangan paul tan, akoo rasa tak juga. DOHC di luar trek boleh ada teknologi VVT yg boleh membantu utk menambah power dan optimize fuel consumption

Chinozie
06-07-05, 09:01 AM
orait...mmg betul...kurang vavle kurang beban...
tp kena ingat benda nie bagus utk tork shj...top aku rase menjerit vavle tu...

PROS

koo bayangkan camnie jerk ek...jumlah minyak masuk same cuma bebanan kerja berlainan...

SOHC lg berat...sbb byk minyak masuk tp...valve kena bekerja keras, kena byk kali buka...RPM tinggi n so on...

DOHC ringan nak nye lg byk valve...valve rilek jooo...buka skit jerk, sbb ade valve lain leh bantu...RPM mase kat higway, rilek jo...cruising...

CONS

SOHC valve besar, korek lg...mungkin pickup utk beberape ratus eter jee laaa leh pegang...pastu tak penin pale pomen nak grand valve..:D :D

badakcipan
06-07-05, 09:19 AM
ader lagik nozie...

secara logiknyer... kalo material yg buat head SOHC ngan DOHC same... campur ngan kompleksiti komponen DOHC i.e. 2 cam, valve lagik banyak... logiknyer DOHC lagik berat darik SOHC :D ....

bazet
06-07-05, 09:27 AM
Mercedes SLR McLaren masih guna V8 SOHC

DOHC
Nih sesuai untuk orang banyak wang, sekali tukar hot cam, tukar 2 batang terus ( twin cam ).

SOHC
Nih sesuai untuk orang yg budget dan suka buat research sebab connecting parts yg kurang, so senang nak paham konfigurasi engine.

Kereta yang guna 20Valve 4 cylinder ( 5valve per cylinder )
Toyota AE111 20Valve
Volvo 850 20valve
Audi A4 20Valve

Chinozie
06-07-05, 09:28 AM
ader lagik nozie...

secara logiknyer... kalo material yg buat head SOHC ngan DOHC same... campur ngan kompleksiti komponen DOHC i.e. 2 cam, valve lagik banyak... logiknyer DOHC lagik berat darik SOHC :D ....

tp dia dibantu dgn dua pulley...tu pasal DOHC byk dipasang pada CC lebih 1.6...kaloo 1.5 mungkin berat skit n tak larat dia nk bawa...

ekzos_pipe
06-07-05, 09:41 AM
In the end, a SOHC 16 valve engine would have better torque on the low end where the DOHC valvetrainís weight results in lower torque. But at high engine speeds, the 16 valve DOHC engineís peak torque and horsepower would be greater. Thatís 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.

Better low end torque ni bukan bagus ke utk jalan yg banyak kornar2?

Chinozie
06-07-05, 10:34 AM
yup...
tu pasal...V6 turbo...tak pick-up...tp top power...tp tu boleh bikin lg :D

FunctionX
06-07-05, 01:01 PM
mengikut penerangan paul tan, akoo rasa tak juga. DOHC di luar trek boleh ada teknologi VVT yg boleh membantu utk menambah power dan optimize fuel consumption

Keyword "ketara".

Matlie
06-07-05, 02:06 PM
Paul Tan nih penulis upahan ker? Hehehe. :P

Setau aku yg tak berapa tahu nih... DOHC ni lebih baik dari SOHC. Tu jerk... detail nya baru aku tahu hari nih. Tapi explanation dr Chinozie tu bagus. Aku rasa ader raleven nya.

edyhensem
06-07-05, 04:41 PM
bagi aku plk DOCH lebih bagus dari SOCH.sbb sperti di atas.dia ringan.beban enjin kurang sikit apa bila kite tekan minyak.

trew
06-07-05, 04:52 PM
nak paham lg jom kita baca ni: http://auto.howstuffworks.com/camshaft.htm ada gamba dgn animasi lg...

wassalam.

gogsard
06-07-05, 04:54 PM
Keyword "ketara".

?? what im saying that .. akoo tak setuju jika perbezaan "ketara" hanya ditrek. perbezaan "ketara" juga boleh nampak pada normal driving.

Chinozie
06-07-05, 05:02 PM
yg korang susah sgt nak pikir wat pee...tah tah paul tan...tan tan sri...mendaaa aaa...ntah org upahan proton...mane laa tau...dia nk upkan savvy...internet ini kena berhati2 tak semua fakta tu betul...kena pandai laaa pikir...jgn percaya pada satu sumber...cari sumber yg lain gak...baru leh clarify...:D

ekzos_pipe
06-07-05, 05:56 PM
tak gak kot, sebab kalau mcm tuh penuh le poket dia, toyota, perodua lagi banyak lagi le upah dia wehh.. ok gak blog dia nih.. banyak info keta..

link ni syok gak:
http://paultan.org/archives/2005/05/31/converting-your-perodua-myvi-to-a-turbo/

Chinozie
06-07-05, 06:07 PM
tak gak kot, sebab kalau mcm tuh penuh le poket dia, toyota, perodua lagi banyak lagi le upah dia wehh.. ok gak blog dia nih.. banyak info keta..

link ni syok gak:
http://paultan.org/archives/2005/05/31/converting-your-perodua-myvi-to-a-turbo/

hahahaha...yg ko percaya aku cakap nape...:D
tah leee...ko nk senang gi tanya pomen...mmg ade betul dia cakap...

kaloo camtu...mase pick-up pakai SOHC...dah top tekan suis tukar head DOHC... :D

bazet
06-07-05, 09:13 PM
http://img407.imageshack.us/img407/7946/rta96ccrank.jpg
SOHC Power.....

bazet
06-07-05, 09:16 PM
Aku nak bercerita pasal sorang pomen melayu kat Klang.

Dia dah guna 4 bijik VR4, semuanya pecah. Enjin terakhir, perdana 1.8 SOHC dengan wiring 4G13p ( angin sedut tanpa batasan ) dan gearbox wira 1.8. Hasilnya dia dapat power yang seimbang untuk layan BTSC dan enjin tahan lama ( long term financial ).

Tuh cerita sebelum BTSC tutup, skrg dah main rotary pulak...takder lagi pakai piston.

FunctionX
06-07-05, 09:31 PM
bazet.. itu dah jauh dah tu... 400,000hp @ 500rpm.... tak main la..

dan aku ingat paul tan cuma cerita pasal conventional sohc vs dohc. Tak masuk lagi variable timing & lift....

vtecinside
07-07-05, 09:56 AM
yang aku tau la dohc lagi power dari sohc...dari penjimatan sohc lagi jimat...tapi tak mustahil bole upgrade sohc untuk lawan dohc

bazet
07-07-05, 12:20 PM
Kita ambil aja contoh mudah depan mata

Proton Waja powered by Mitsubishi 4G18P
1600cc SOHC
- Takder komplen pasal low torque power. walaupun enjin 1.6 aja, tapi boleh bawak body Waja yg berat tu.

Proton GEN2 powered by CamPro
1600cc DOHC
- kebanyakkan komplen pasal power takder until tekan sampai 4000rpm ke atas. Takkan nak memanjang high rev sampai 4000rpm powerband. Ada orang kata, ketiadaan sistem Cam Profiling menyebabkan low torque tuh tak ada langsung.

Mac Weng
07-07-05, 01:00 PM
nape tak compare jer enjin mitsubishi SOHC ngan DOHC...kalo compare campro memang ler.....enjin pon baru2 jer nak naik..

Matlie
07-07-05, 01:49 PM
Bazet, tu enjin titanic ka? Besar gedabak tu...

edyhensem
09-07-05, 10:54 AM
yer lah besar sagat head dan cam kat atas tu.
mamag bajet lebih kalo pakai DOCH tapi kena inggat kite senag nak memotong atau senang nk merimpit kat org yg ngada2.yg tujuk exsen kete dia org laju

FunctionX
09-07-05, 05:16 PM
tu crank la.. bukan cam....

ekzos_pipe
11-07-05, 10:08 AM
minyak fully sintetik le tuh agaknya.................

vtec jazz ngan city yg single cam sape dah try? okeh tak? tapi dulu ada satu vtec awal2 punya la 1.5 sohc gak.. d15b ke hape tah, standerd dalam 128hp le gak..