Comments on: SOHC vs DOHC Valvetrains: A Comparison

By: Rave

Rave — Tue, 15 May 2012 03:14:58 +0000

hi Paul and forumers,
i am using waja auto 4g18 sohc.recently i found a shop at sg buloh who transform sohc head to dohc head package.he did few cars n only 4g18 sohc engine.
plan to change to dohc head.the price is rm2k.
any comments?

By: tawajas

tawajas — Wed, 01 Feb 2012 23:44:02 +0000

heyy Paul
can u plz tell me which one’s more fuel efficient…
dohc or sohc…

i want sme real advice as i want to buy a bike in Indian market n my choices are KTM Duke 200 (dohc) & Bajaj pulsar 200 ns (sohc)…

my priorities are performance, durability, low maintance, fuel efficiency…

m more leaned towards Duke 200 bt m suspicious of its fuel efficiency as pulsar 200 ns is offering a huge 58 kmpl…

plz do reply…

i’d b greatful

By: Eric

Eric — Wed, 26 Oct 2011 15:19:33 +0000

brilliant!

By: mitch eppler

mitch eppler — Sat, 18 Jun 2011 03:00:12 +0000

you jump back and fourth between sohc and dohc info,too many words.Give me some specs.I will let you pick the cars

By: ProDigit

ProDigit — Sat, 27 Nov 2010 04:19:07 +0000

in other words a SOHC engine technically would use less gasoline (better mpg) for the fuel conscious driver?
Because you can run the engine at lower RPM’s, have better torq there, the engine sucks less gasoline at lower RPM’s, and the engine’s bearings last longer (lower RPM means less heat; high revs are especially worse on a cold engine).

By: Abhishek

Abhishek — Wed, 06 Oct 2010 13:32:23 +0000

Thank you author for this informative post. I just had a query…

In the beginning paragraph you have mentioned that,

“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”, but in the concluding paragraph it is written that,

“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”.

I am a bit confused about which one is better according to the city driving conditions where frequent grear shifting is needed and secondly, which one would be better in terms of ‘fuel-efficiency’.

I request you to please clarify on this, thank you.

Abhishek

By: Kentthegreet

Kentthegreet — Mon, 20 Sep 2010 05:48:25 +0000

Hi Paul,

Thanks for this very informative blog. I have a question in summary. If I am only in normal driving like going to office and home and off town vacation at normal speed, should I get the SOHC? What about the SOHC’s fuel consumption compared to DOHC?

Thanks.

By: miker

miker — Sat, 18 Sep 2010 03:17:50 +0000

as for me, power and torque depends on the cam lobe profile, the lift and valve opening/closing degree. as an example, daihatsu acsend 1.6 SOHC 16v engine, and high performance daihatsu charade detomaso 1.6 SOHC 16v using a same engine but different in cam profile. it produces a different output. single cam engine normally uses a rocker arm as a link between cam lobes to valves. so, there will be much more friction, (cam lobe to rocker arm, rocker arm itself and rocker arm to valve). because of this, single cam engine cannot be design to rev higher, high rpm produces higher BHP per cubic capacity. ” to produce high power, sacrifice the torque” vtec, dvvt, vvti, tvis, cps, etc, engine is design to automatically ”tweak the sentence” by means of opening more valve, lifting the valve wider, or longer on certain RPM so that we can get both torque and power when we needed the most.

By: helman

helman — Wed, 11 Aug 2010 14:14:35 +0000

can you give more???

By: Matt

Matt — Sun, 11 Jul 2010 08:51:19 +0000

When you say “A stiffer spring means more energy has to be spent overcoming the valve pressure”, are you forgetting that the same amount of energy is returned. That said, stiffer springs do create more friction…
Also, the rockers in an SOHC add to the reciprocating mass. And you cant have a 4v SOHC without rockers. There’s no arguing the low end punch of an 2v SOHC though (look at the 205gti).

By: amal

amal — Fri, 18 Jun 2010 13:56:32 +0000

thanks man. great work….!

By: Kevin W

Kevin W — Thu, 20 May 2010 18:24:34 +0000

Hi Paul, do u know is Ford Ranger 2.5cc TDI/WLT SOHC a 12 valve or 16 valve design?

Please advise,

regards,
Kevin.

By: Beryuyuyuyu

Beryuyuyuyu — Thu, 15 Apr 2010 23:29:38 +0000

Daily driving, they’re both more or less Equal I’d say. Unless you were racing with a stock motor, the DOHC takes it. But if you were racing, both of the motors etc would be modded which kinda balances everything out. Because who would wanna risk those high rpms with a stock motor?

By: KCivic

KCivic — Sun, 11 Apr 2010 14:19:16 +0000

Its amazing that ppl are using this Blog for reference and information related to cars and driving cos after original posting of this dohc vs sohc article since mid 2005, ppl are still sharing opinions here. I always tot driving dohc is better than sohc or more powerful.

By: Robin

Robin — Wed, 07 Apr 2010 05:11:28 +0000

Good. Very informative.

By: speedfreak

speedfreak — Wed, 10 Mar 2010 12:19:37 +0000

which is better in terms of speed?OHV or OHC?lets say that the speed that we need to meet is like 160km/h

which is better to get to the said speed?

By: Lee Debono

Lee Debono — Tue, 09 Feb 2010 15:41:09 +0000

Nice Post there Paul.

1 small thing that id like to point out.

In Nissan's the D after the litre-age (either 20 – 2.0 litre, 24 – 2.4 litre or 30 – 3.0 litre) means that its a DOHC.

The VG30E is a SOHC engine.

The VG30DE is a DOHC engine.

So you technically you did show the difference between the DOHC and SOHC systems.

By: Guilherme

Guilherme — Fri, 08 Jan 2010 08:32:41 +0000

Great article, but you got some things wrong.

Having a single big valve doesn't effect low-rpm torque negatively, because the valve has plenty of time to open and close. The "hose" argument doesn't apply here, simply because when you use two valves, each valve gets only half the air mass as a larger one would get, therefore, pressure is equal (assuming the smaller valves have half the diameter of the big one).

Another thing is that your conclusion that DOHC has more peak power than SOHC depends on other factors. The good old Honda D16 was offered in many configurations, and at one point in the late 80's, in Europe, it was possible to have either SOHC 16V or DOHC 16V, with all other things being equal.

Power ratings for the engines were:

SOHC 16V: Power – 115hp@5900 rpm, Torque – 13.9kgfm@4800 rpm

DOHC 16V (Civic): Power – 125hp@6800 rpm, Torque – 14.9kgfm@5900 rpm

DOHC 16V (Integra): Power – 118hp@5600 rpm, Torque – 14.3kgfm@4800 rpm

From these numbers, one can see that the DOHC version used in the Integra has an earlier power peak than the SOHC, while the DOHC Civic indeed has more power and at higher rpm than the SOHC Civic. Later SOHC VTEC iterations of the engine would deliver more power and have a longer powerband than any of the listed engines.

So I think a better conclusion would be that all things being equal, DOHC engines have more potential to have more power than a SOHC engine due to the finer control of valve timing. However, DOHC engines are more complex, less reliable, weigh more and are more expensive than a SOHC design, which explains that Honda was right in their decision to switch back to SOHC, as they can achieve similar performance results.

By: paco paquito

paco paquito — Fri, 18 Dec 2009 13:53:42 +0000

newer engine like R18 or R20 in honda went full circle went they all came back to SOHC instead of DOHC. a number of followers questioned this honda moved. honda explained that going back to SOHC but an improved configuration based from the legendary D15B vtec SOHC has all to do with weight. the K20 is so nose heavy that in a quarter mile a lighter R20 (lighter than a D16 i heard) could readily smoked it. by introducing a simple set up with SOHC configuration in recent variants like the new crv and 2009 lines honda choose weight as the end of it all.

By: Saibal Das

Saibal Das — Thu, 01 Oct 2009 15:26:06 +0000

Being a marine engineer i always work with pushrod-rocker type engine( medium speed diesel engine) or hydraulically operated exhaust valve( slow speed diesel engine) and i donot have any exposure to petrol/gasoline engine. my question is there any cam follower in the dohc system and how the valve clearance is adjusted? how valve timing is adjusted?

By: vikas

vikas — Fri, 11 Sep 2009 21:46:11 +0000

kindly advice fire 1.4 starjet in linea is better than ford duratech technically or if compare fire with duratech and i vtech which is best

By: KK

KK — Sun, 16 Aug 2009 14:53:41 +0000

Hey!!!! This is a really good piece of info. Really informative. Keep up the goodwork…..

By: Frank

Frank — Mon, 10 Aug 2009 00:32:58 +0000

Thanks for the info. But for a layman …all I want to know is ….the new 2009 Honda Accord 2.0 VTiL has a SOHC configuration while the older generation 2005 Honda Accord 2.0 iVtec has a DOHC configuration . Just tell me which is better !!! Thanks .

By: Frank

Frank — Mon, 10 Aug 2009 00:31:52 +0000

Thanks for the info. But for a layman …all I want to know is ….the new Honda Accord VTiL has a SOHC configuration while the older generation has a DOHC configuration . Just tell me which is better !!! Thanks .

By: Cicma

Cicma — Sat, 08 Aug 2009 07:27:59 +0000

Low end and High end is referred to the RPM's, that means to low RPMS (a soft drive) or high RPM (accelerating to the top), so when you are a high speeds your engine will need be in high end (High RPM's) to maintain the power (velocity) that's when a DOHC is better. Of course that was just an example, also depends of the engine configuration; so if you like rev your car a top that means drive fast with fast shift changes its better a DOHC, but if you drive smooth in the city you will no need a DOHC and with SOHC would be enough, the difference could be more noticed, as said, in how many valves per cylinder the engine has

By: frank

frank — Sun, 19 Jul 2009 23:21:39 +0000

SOHC has better low-end power, DOHC has better high-end power and overall maximum power.

what do you mean by low end power and high end power ? from your conclusion DOHC is better ??

By: ken nguyen

ken nguyen — Fri, 22 May 2009 06:25:15 +0000

I just visited a Dodge dealer. I saw the Grand Caravan I like very much, but one of the main differences between its engine and the toyota minivan is the SOHC (toyota van has DOHC). I wonder if this makes the Toyota more reliable van, but after reading your article, I understand this is not the reason why Toyota is more reliable. Thank you!

Ken N.

By: Yantho

Yantho — Sat, 11 Apr 2009 16:27:45 +0000

hey paul, i've had a mazda 323f 1.6L 16v dohc for ebout 250000kms, now i've bought the exact same car but in a 1.8L grsi 16v dohc version at around 175000kms,

now i'm looking to transplant some parts from my old one, but i can't quite get my finger around that grsi thingy sticking on to the back end like ted kennedy on a hogie, what does it mean, and is it possible to somehow supercharge the engine (turbo)? as you have no doubt guessed i know jack about car engine's but i know what i like so can anyone help, some tips on how to do this, and what grsi stands for?

cheers,

By: Charlie Bader

Charlie Bader — Tue, 07 Apr 2009 12:50:40 +0000

You left out the biggest reason for 4 valves/cyl- valve area. The total area of the valves is much greater because the non-valve area is smaller with 4 valves. It's like the jar of marbles problem- you can fit more in if the particles are smaller.

By: pranesh

pranesh — Sat, 21 Mar 2009 23:29:18 +0000

its great dude.. can u give more detail over the complication of having 4 valves in sohc and explain me the example 4G92P which you have used…

if possible post to my mail…please…..great work