Difference between DOHC Vtec and SOHC i-vtec

[Bob san]

Just wondering what are the main differences between DOHC vtec and SOHC i-vtec.

[**Ghost**]

Essentially speaking the biggest difference is the number of camshafts the engines have.

DOHC = DUAL overhead camshafts

SOHC = SINGLE overhead camshaft

DOHC engines are designed to rev higher, have peakier power outputs and PERHAPS high horsepower application.

SOHC engines are designed to make power low in the rev range, have more usable power for daily driving.

[Bob san]

So does that mean DOHC is usually more powerful then SOHC?

[yeehou]

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. 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. (copied from a website)

[marte]

ivtec = vtec (valve timing & lift control) + VTC (Variable overlap timing control)
the vtec is the same as the current DOHC B Blocks but with something new vtec-e, this is something that concentrates on mild cams.
ivtec is the way to go.

[Sexc86]

dam i am waiting for weq to have his 2 cents ;)

[aimre]

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. 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. (copied from a website)


Well our engines are straigh fours, so we got one head, and onyl two cams in total.

[marte]

plus i-vtec enginesa are newer lol

[ROLLED]

ivtec = vtec (valve timing & lift control) + VTC (Variable overlap timing control)
the vtec is the same as the current DOHC B Blocks but with something new vtec-e, this is something that concentrates on mild cams.
ivtec is the way to go.


personally, I wouldn't listen to a man who resprayed his car green! LOL

[marte]

personally, I wouldn't listen to a man who resprayed his car green! LOL


haha you idiot ill put pink paint on ur car :)

[Limbo]

I believe the SOHC does not have lift whilst the DOHC has lift feature in the Vtec.

SOHC only has timing adv.
DOHC has Cam profile change & timing adv, ignition and exhaust.

[aaronng]

SOHC VTEC = Timing and lift change in 1 step. Usually used to maximise low end torque. Because 1 cam controls both intake and exhaust valves, you cannot get good timing for high RPM power.

DOHC VTEC = Same as above, but because intake and exhaust are on separate cams, you can have very wild cams timings, duration and lift for high-cam.

VTEC-E = VTEC is used to close 1 intake valve at low RPM. So it operates at in 12 valve mode in low RPM for torque and 16 valve mode at middle to high RPM. Intake cam has 2 lobes but 3 followers. The extra follower is for the closed intake cam.

3-stage VTEC-E = Same as above, but in addition to 12v and 16v, there is a a 3rd stage where the large middle cam love for intake is used. So you have more power.

SOHC VTEC (Jazz): has 12v and 16v mode like VTEC-E.

i-VTEC (DOHC low performance, CRV, Accord): VTEC only on the intake cams, and also VTC on intake.

i-VTEC (DOHC high performance, DC5R, DC5S, Accord Euro): VTEC on intake and exhaust cams, and VTC on the intake cam.

i-VTEC SOHC (new, 2006 Civic): At low loads, the intake valve closure is delayed well into the compression stage so that part of the intake goes back out the intake valves. This reduces pumping loses for low load situation. At high load or heavy throttle, the intake valve closure becomes normal using VTEC, so it works like a normal engine. Those who know their engine types will notice that this is a Miller Cycle-type engine when the intake valve closure is delayed. Plus, VTEC can be activated at ANY RPM! A hydraulic pump increases the pressure of the engine oil at low RPM so that there is sufficient pressure to use the VTEC system. Oh, and VTC on the intake cam.

And yes.... I wrote this all from memory. :p

[JaCe]

Wow you know alot about the i-VTEC SOHC on the 2006 Civic... when you say VTEC can be activated at any RPM, what do you mean exactly? I think it feels like there is a surge after 2000rpm.

[aaronng]

Wow you know alot about the i-VTEC SOHC on the 2006 Civic... when you say VTEC can be activated at any RPM, what do you mean exactly? I think it feels like there is a surge after 2000rpm.
Yup, it can be activated at any RPM. It could be 2000rpm, it could be 3000rpm, it could be 4000rpm. It all depends on the engine load and the amount of throttle you are giving. Based on engine load and throttle position, the ECU sends a signal to the hydraulic actuator so that the oil pressure is increased and can still operate the VTEC mechanism when the solenoid is activated.

When VTEC is activated, the engine runs like a normal engine that is out of VTEC. When not in VTEC, the engine is running in high efficiency mode (Miller cycle). But... your surge that you feel is not really from VTEC, but from your special intake manifold. If you look at the intake manifold on normal Honda engines, you see 4 tubes into the block (intake manifold in front for K and R series, at the back for B and H series). Your 06 Civic 1.8L has a twin length manifold. Long for low RPM and short for high RPM. So at high RPM (I'm not sure what RPM it is set to switch at), you get better breathing.

Pics here to show you the difference. (links I found on google).
Short: http://www.jazzproparts.com/photos/K20A-2.jpg
Long: http://www.a-oktw.com.tw/CD/AOK%20NEW%20FILE/HONDA/K20A.JPG

Examples of Hondas with short intake manifold: Integra DC2R, DC5R, Civics with b16a and b, EuroR.

Hondas with medium intake manifold: Accord Euro

Hondas with long intake manifold: CRV, Accord VTi, Integra Luxury, Jazz

Hondas with dual length manifold: 06 Civic VTi(L), DC2 Integra.

[Limbo]

aaronng has honda give you a job in their tech dept yet mate?
I'm suprised you mange to rem all that.
I can't even rem my number plate number!

[aaronng]

Haha, it's easy for me to remember these technical things because I've been technically-inclined since young. My dad used to tell me that when I was young (2 years old), my favourite toy was a pad lock and a bunch of keys. My past time was finding out which key opened the lock. LOL

[jkz]

Yup, it can be activated at any RPM. It could be 2000rpm, it could be 3000rpm, it could be 4000rpm. It all depends on the engine load and the amount of throttle you are giving. Based on engine load and throttle position, the ECU sends a signal to the hydraulic actuator so that the oil pressure is increased and can still operate the VTEC mechanism when the solenoid is activated.

When VTEC is activated, the engine runs like a normal engine that is out of VTEC. When not in VTEC, the engine is running in high efficiency mode (Miller cycle). But... your surge that you feel is not really from VTEC, but from your special intake manifold. If you look at the intake manifold on normal Honda engines, you see 4 tubes into the block (intake manifold in front for K and R series, at the back for B and H series). Your 06 Civic 1.8L has a twin length manifold. Long for low RPM and short for high RPM. So at high RPM (I'm not sure what RPM it is set to switch at), you get better breathing.

Pics here to show you the difference. (links I found on google).
Short: http://www.jazzproparts.com/photos/K20A-2.jpg
Long: http://www.a-oktw.com.tw/CD/AOK%20NEW%20FILE/HONDA/K20A.JPG

Examples of Hondas with short intake manifold: Integra DC2R, DC5R, Civics with b16a and b, EuroR.

Hondas with medium intake manifold: Accord Euro

Hondas with long intake manifold: CRV, Accord VTi, Integra Luxury, Jazz

Hondas with dual length manifold: 06 Civic VTi(L), DC2 Integra.

When you refer to the dual length manifold for the civic 06. Is it only both VTI L and VTI or just VTI L?

[aaronng]

When you refer to the dual length manifold for the civic 06. Is it only both VTI L and VTI or just VTI L?
WHoops. Both the VTi and VTiL are mechanically the same. So yeah, they both have the dual length manifold.

[JaCe]

Ahh thanks for that info aaron. I know this is going out on a whim a bit and is probably a subjective Q, but I've seen other Honda cars with i-VTec too; but they aren't the new Civic. Since they are DOHC, does that mean they are more advanced/better than my car?- or does i-VTec mean different things under different circumstances?

And thanks again for the info. It's pretty awesome. I think my car is starting to perform considerably better now that it's run-in (past the 3.5k mark).

[aaronng]

Ahh thanks for that info aaron. I know this is going out on a whim a bit and is probably a subjective Q, but I've seen other Honda cars with i-VTec too; but they aren't the new Civic. Since they are DOHC, does that mean they are more advanced/better than my car?- or does i-VTec mean different things under different circumstances?

And thanks again for the info. It's pretty awesome. I think my car is starting to perform considerably better now that it's run-in (past the 3.5k mark).
All VTEC does is lets you use 2 cam profiles for your engine. Which means you have 2 RPM ranges where your engine can perform optimally. Each VTEC system is set based on what are the target objectives of the engine. In a performance orientated engine like the K20A, the objective is power, power and more power. For city cars like the Jazz, VTEC is used to run the engine in 12v mode for better low end torque so that the small engine can still have enough torque when you are in a traffic jam and can only rev to 2000rpm.

The civic on the other hand is made for todays world of high petrol prices. So its focus is fuel economy. That's where its VTEC is used. But, eventhough it is an engine designed for fuel economy, Honda put in molybdenum-coated pistons (DC2R engines and Jazz VTi), dual length intake manifold (DC2 VTiR engines), piston oil jets for maximum cooling and lubrication (only in the S2000 and K series engines) to have fuel efficiency and also power (103kW).

Compare it to its rivals in the same 1.8L segment:
Nissan Tiida: 93kW
Holden Astra: 90kW
Toyota Corolla: 93kW (used to be 100kW)

Want to compare it to more upmarket cars?
BMW 118i (2.0L): 95kW
Renault Megane 2.0L: 99kW
Ford Focus 2.0L: 107kW

So the civic's 1.8L has super fuel efficiency due to i-VTEC and yet has more power than other 1.8L rivals due to the special tweaks that have been used in higher performance engines.

Is that advanced? I'd say so. Any car company can use variable valve timing and lift to make lots of power. But none of them tried to make good power and yet have good fuel economy. Remember, most car companies get fuel economy by using drive by wire, variable valve timing, exhaust gas recirculation, throttle shut off when cruising. The Civic does all this and goes further. Only 2 cars has tried to use the same miller cycle system. That was Mazda Eunos 800 and a Subaru Turbo Hybrid. You probably have not heard of these cars because they were not that successful and their miller engines did not give any fuel efficiency benefits. They had to put a supercharger on to regain useful power and in the end negated the benefits. Honda did it with their VTEC system. Every car company uses VTEC/VVTL-i/VANOS/MIVEC/VVL to make power. None of them tried to exploit valve control to make a miller cycle engine that does not produce any less power than a normal engine!

[JaCe]

Wow. Thanks again :)

I think that the transmission/drivetrain also plays a pretty important role because even though the Astra has 90kW... when you drive it (at least in automatic rendition) it feels like a slowpoke. Comparatively the Civic, whilst only 13kW more, feels considerably more powerful under all circumstances.

[aaronng]

Wow. Thanks again :)

I think that the transmission/drivetrain also plays a pretty important role because even though the Astra has 90kW... when you drive it (at least in automatic rendition) it feels like a slowpoke. Comparatively the Civic, whilst only 13kW more, feels considerably more powerful under all circumstances.
That's because it doesn't have any efficiency work done on it. No variable valve anything to boost low RPM torque. So its number are only valid when at close to the peak power and torque RPM

[|N|]

this man deserve some rep points

[Bob san]

JACE, do u drive an auto? wot Rpm do u feel like the torque starts coming in?

i drive manual and its usually round 4000revs u start to feel it.

[Limbo]

+ rep for you aaronng

[kuso]

Tell me more about the jazz vtec. Is it even i-vtec? It just says vtec on the engine cover. I know its offtopic but want to know.

+ 1 rep point!

[aaronng]

LOL, typing this while watching soccer.

Jazz 1.5L VTEC is not an i-VTEC because it doesn't vary the intake cam timing. Instead, it is a 12/16v VTEC system. Below 3500rpm, one of the intake valves is closed so that the intake comes in from one side and the shape of the piston head directs the charge so that it swirls around in the head for complete burning. So you get good torque at low rpm. Above 3500rpm, 1 intake valve is not enough to fill the cylinder quick enough, so both valves are opened by VTEC. So effectively, you get double the intake area above 3500rpm. So when you look at dynos of the torque chart, the torque is higher as your RPMs increases. Opposite to that of economy engines where the torque is high at the middle rpms and starts to taper down as RPM increases. The engine also has molybdenum coating on the piston skirts (it was the first non-performance honda engine to get it), while the intake manifold is divided into 2 so that the 2 farthest cylinders still get enough air without being blocked by the closest 2 cylinders.

What else... hmmm, I think the Jazz VTEC also has stainless steel headers! Someone check underneath their car to confirm this! It should be nice and shiny. Opposite to my Accord euro with steel headers that are dull and brown.

[JaCe]

This thread makes me wish that Honda would differentiate between the different VTecs more explicitly.

[roar]

This thread makes me wish that Honda would differentiate between the different VTecs more explicitly.


doesn't matter, we have aaronng

[Honda Enthusiast]

SOHC VTEC = Timing and lift change in 1 step. Usually used to maximise low end torque. Because 1 cam controls both intake and exhaust valves, you cannot get good timing for high RPM power.

DOHC VTEC = Same as above, but because intake and exhaust are on separate cams, you can have very wild cams timings, duration and lift for high-cam.

VTEC-E = VTEC is used to close 1 intake valve at low RPM. So it operates at in 12 valve mode in low RPM for torque and 16 valve mode at middle to high RPM. Intake cam has 2 lobes but 3 followers. The extra follower is for the closed intake cam.

3-stage VTEC-E = Same as above, but in addition to 12v and 16v, there is a a 3rd stage where the large middle cam love for intake is used. So you have more power.

SOHC VTEC (Jazz): has 12v and 16v mode like VTEC-E.

i-VTEC (DOHC low performance, CRV, Accord): VTEC only on the intake cams, and also VTC on intake.

i-VTEC (DOHC high performance, DC5R, DC5S, Accord Euro): VTEC on intake and exhaust cams, and VTC on the intake cam.

i-VTEC SOHC (new, 2006 Civic): At low loads, the intake valve closure is delayed well into the compression stage so that part of the intake goes back out the intake valves. This reduces pumping loses for low load situation. At high load or heavy throttle, the intake valve closure becomes normal using VTEC, so it works like a normal engine. Those who know their engine types will notice that this is a Miller Cycle-type engine when the intake valve closure is delayed. Plus, VTEC can be activated at ANY RPM! A hydraulic pump increases the pressure of the engine oil at low RPM so that there is sufficient pressure to use the VTEC system. Oh, and VTC on the intake cam.

And yes.... I wrote this all from memory. :p


So all in all, what's better and more powerful SOHC or DOHC??

[[[d a n n y]]]

So all in all, what's better and more powerful SOHC or DOHC??

read again
DOHC is better

[Honda Enthusiast]

]']read again
DOHC is better


Yeah, but Aarong said SOHC does everythign in 1 step?

[aaronng]

Yeah, but Aarong said SOHC does everythign in 1 step?
For power, the DOHC Honda engines have more aggressive cams and thus makes more power per litre. The SOHC honda engine is designed for fuel economy.

[mastcell]

Sorry for my ignorance on this subject as I am still learning about these concepts, however, the Atkinson cycle is probably a more appropriate name for what Honda is trying to do with the i-VTEC in the 06 Civic.

The main difference between Miller cycle and Atkinson cycle is that Miller cycle always use supercharger to compress the charge. The Atkinson cycle is a Miller cycle without the supercharger, so it provides efficiency at the expense of power.

In the Miller cycle engine, a supercharger 'over-compress' the fuel-air mixture. When the piston moves upward to compress this charge, the valve is allowed to open for longer than usual, so some of the charge is pushed back out into the intake manifold. This would normally result in a loss of power (as in Atkinson engine) but in a Miller engine, the charge is already 'overfed', hence the net benefit is that less energy is required to move the piston during compression stroke, while still maintaining the same end point compression ratio, and the same power during ignition/power stroke.

The Miller cycle engine is advantageous as long as less energy is used by the supercharger to compress the fuel-air charge than what the piston would use during compression stroke. This is where VTEC is can be used to increase the valve timing when the advantages are present.

I know some part of what I said contradict aaronng's posts, I could be wrong conceptually and I don't know enough about Civic engine to comment on specifics. I am open to suggestions...

[aaronng]

^^ You're correct. A miller cycle engine without a forced induction to bring up the filling efficiency is called an atkinson cycle engine.

Why did I refer to the miller cycle instead? Because I was trying to illustrate that where Mazda used a supercharger to overcome the drawbacks of the atkinson cycle, Honda instead used i-VTEC to do the same.

R18's SOHC i-VTEC allows the same effect of the miller cycle but without the fuel consumption drawbacks of forced induction. It allows the engine to run in the (less than 1.8L) atkinson cycle while cruising and back to the 1.8L otto cycle when under acceleration.

[mastcell]

Thanks for the explanation, aaronng. :)

[xenfacta]

Plus, VTEC can be activated at ANY RPM!

loving this! my voice might get a bit sore from always shouting
http://www.geocities.com/tyrome87/vtec.jpg

nice work aarong.. i was wondering why there wasnt a big vtec kick during full bore acceleration... now i know why.. its always on, yo!

[Silver_EH]

no cams r better :) but if u must... DOHCs r "better" not because u can have wilder cam profiles or durations... because u can have the same in sohc engines... u could even have an extremely wild cam in a buried motor "pushrods" fastest drag cars in the world use 1 cam :P and make 7000hp+ but for street and tunability and probably cost.. dohc is the way to go.. oh and btw.. they dont rev harder.. thats the dumbest thing ive ever heard

[aaronng]

no cams r better :) but if u must... DOHCs r "better" not because u can have wilder cam profiles or durations... because u can have the same in sohc engines... u could even have an extremely wild cam in a buried motor "pushrods" fastest drag cars in the world use 1 cam :P and make 7000hp+ but for street and tunability and probably cost.. dohc is the way to go.. oh and btw.. they dont rev harder.. thats the dumbest thing ive ever heard
For low rev applications, SOHC is more efficient because of lower valvetrain resistance (only 1 cam rotating). But at high rev of above 6000rpm, the larger mass of the valve rocker arms have too high an inertia requiring much stronger valve springs to compensate. Rocker arms used in DOHC engines are much smaller as the cam sits directly on top of the valve, so there is less inertia and it is more reliable at high RPM.

The reason why everyone says DOHC for wilder cam profiles is because when you use wilder cams, you need a higher RPM limit to take advantage of pushing the peak torque up higher in the RPM range. DOHC for high RPM reliability :thumbsup:

[daniel b16a]

so basically sohc low end power and dohc lil low end power but lotsa high end power

[silver_screen]

no his wrong in both aspects... both cams can be used for either application

u can rev the shit outta any car, doesnt matter how many cams it has. like i said earlier under my fiances nick... the fastest, most powerful cars arent twin cams.. they use 1 cam... and the rev to 10k+ and make 7000hp+ :)

sure twin cams make things easier and possibly more efficent but rev harder and wilder cams r just a myth... btw do u work on cars aarronng?? as a profession???

[dannybubu]

god damn...when did you learn all that stuff aaronng???

[aaronng]

Be an engineer and all things mechanical are interesting.

[silver_screen]

i too am an engineer.. mechanical engineer @ that and im also an automotive technician :) Neither cam will rev harder than the other or make more power as a total if money is put into it. the thread was meant to be which vtec is better... sohc or dohc.. in the case of a honda dohc is better because it makes more power and revs higher but not because it has an extra cam, but because the head itself flows more air. the cam also has a higher lift and duration than its sohc counter part. The bottom end is also better balanced and has stronger internals than the sohc which allow it to rev higher. depending on how much money u spend on a design, in almost any case.. a DOHC head will flow more than a SOHC head. In almost all cases also, a SOHC will not make more power than a twin down low either. In any case... having no cams at all r even better from a mechanical loss point of veiw ;) lol