what is Vtec / I-Vtec / 3 Stage Vtec ? Definitions Inside !!

source: http://www.leecao.com/honda/vtec/

for all of you who didn't exactly know what the differences are ( like myself )



What is VTEC ?

VTEC is an acronym for Variable valve Timing and lift Electronic Control. It is a mechanism for optimizing air/fuel mixture flow through the engine.

An internal combustion engine converts the chemical energy stored in fuel into thermal energy. The increased thermal energy within a cylinder causes the pressure to build. This pressure acts on the pistons and the result is a mechanical force rotating the crankshaft. This mechanical force is measured as crank torque. The ability for the engine to sustain a certain level of crank torque at a certain RPM is measured as Power. Power is the rate at which the engine can do work. This conversion process is not 100% efficient. In fact, only about 30% of the energy stored in the fuel is actually converted into mechanical energy.

Physics says that for a given efficiency level, a higher rate of fuel consumption is needed for the engine to generate power. So it becomes obvious that if you want more power, you need to increase the rate of fuel combustion. One way to achive this goal is to have a bigger engine. A bigger engine with larger cylinders will be able to combust more fuel per rotation than a smaller engine. Another method is to pre-presurize the fuel/air mixture and cram it into an existing engine size. Thus even though the cylinder size stays the same, more fuel is combusted per rotation. This second method is referred to as forced induction.

Honda chose to explore another method: keep the engine size the same, but turn the engine faster to consume more fuel. Here is an analogy: You want to move foam peanuts from one bucket to another with a cup. You can increase the size of your cup, compress/cram as much peanuts as possible into the cup each time, or you can just move the cup faster. All three methods moves more peanuts. Honda uses the last method. And again, more fuel combusted equals more power generated by the engine.

As the engine speed is increased, more air/fuel mixture needs to be "inhaled" and "exhaled" by the engine. Thus to sustain high engine speeds, the intake and exhaust valves needs to open nice and wide. Otherwise you have what is akin to athsma: can't get enough air/fuel due to restrictions.

If high speed operation is all we have to worry about, Honda wouldn't need to implement VTEC. Indeed, race engines that operate mostly at high rpms do not utilize any mechanism like VTEC. But street cars used for daily driving spend most of their time with the engine at low RPMs. Valves that open wide for high RPM operation contributes to rough operation and poor fuel economy at low RPMs. These undesirable traits are directly against Honda's design goals.

The solution that Honda came up with is the VTEC mechanism: open the valves nice and wide at high RPMs, but open them not as much at low RPMs. So now you have a engine with smooth operation at low RPMs, and high power output at high RPMs.

And that is basically what VTEC is. It's nothing magical. The idea has been around for a long time. Honda's VTEC is just a very simple, elegant and efficient implementation that is extremely effective at achiving its design goal. Honda automobiles are the first among modern automobiles to utilize this mechanism in such a large scale of distribution.

What do I want it ?

VTEC, like most things in life, is not for everyone. To decide whether VTEC is for you or not, here are the pros and cons.

Pros

The main benefit of VTEC is that the resulting engine is very versatile. The torque curve is very flat: among the flatest of all the engines on the market. Thus where other engines are running out of breath, a VTEC engine maintains a nice and steady output of torque, making the whole RPM range usable for acceleration. So when you are just driving around at a reasonable pace, the car is very smooth and fuel consumption is similar to other engines of the same displacement. When you need more power for passing, all you have to do is down shift and take advantage of the extra power available at the higher RPMs. So you get the smoothness and fuel efficiency of a small economical engine when you drive a low RPMs, and the power output of a much larger engine at high RPMs.

Due to the greater range of usable RPMs, shorter gears can be used. Thus for any given speed or engine RPM, a VTEC engine will allow for a larger ratio multiplier, resulting in more wheel torque. Thus the benefit of the VTEC technology in terms of acceleration improvement also affects low RPM operation.

Since VTEC creates more power without increasing displacement, the engine is likely to be smaller and lighter.

Cons

A vehicle achives its greatest acceleration by keeping the engine RPM as close to the HP peak as possible. And for DOHC VTEC engines, this means keeping the needle at some rather lofty RPMs, and more frequent shifts to keep the RPMs up. To some people, including yours truely, this is a desirable trait: lots of driver involvement in the process of extracting excellent performance. To others, especially those accustomed to the Kansas-flat HP curves of muscle cars, the high RPM and frequent shifts become bothersome.

For a good launch off the line, such as at the start of a drag race, a certain amount of tire spin is desired. Muscle cars have torque peaks at low RPMs, and then taper off as the RPM builds. This is perfect for drag racing as the initial torque peak generates the desired tire spin, and then the lower torque at higher RPMs allow the tire to find and maintain grip. But DOHC VTEC's torque curve is very flat, so the initial tire slip is much harder to generate. And once the tire looses traction, the flat torque curve makes it hard for the spinning wheels to find traction. So to properly launch a DOHC VTEC car, the driver must slip the clutch at high RPMs to generate the initial tire spin, and then carefully modulate the clutch and gas to regain drive wheel traction while maintaining maximum acceleration.

Even though Honda's VTEC engines has lived up to the legendary reliability of Honda products, the fact remains that having the VTEC mechanism adds complexity and cost.

more coming below

Honda first introduced the DOHC VTEC mechanism in the US on the 1990 Acura NSX. But a year earlier in 1989, the Japan Domestic Market got the world's first dose of DOHC VTEC in the 1989-1993 generation of the Honda Integra. The 1989 DA6 Honda Integra RSi/XSi used a 160ps variant of the B16A DOHC VTEC engine. Honda enthusiasts would recongnize the B16A engine since it is currently used in the 1999 and 2000 US-spec Civic Si and Canada-spec Civic SiR. However the B16A used in the current Civics is a second version of the original B16A. The main difference is that the newer US-spec B16A has slightly more power at 160hp.

Okay that's enough history. Lets see how DOHC VTEC works. The figure to the right shows a simplified representation of a intake-valve VTEC mechanism (the exhaust mechanisms work similarly). So for each pair of valves, there are three cam lobes. The two on the outside are low RPM lobes and the one in the middle is the high RPM lobe. The two low RPM lobes actuate the two valve rockers, which in turn pushes the valves open. The high RPM lobe actuates a follower, which is shaped like a valve rocker, but doesn't actuate any valves. The figures show the circular section of the cam lobes touching the valve rockers, and the eliptical section pointing away. Thus the valves are closed in this stage.



During low RPM operations, the two outer cam lobes directly actuates the two valve rockers. These low PRM lobes are optimized for smooth operation and low fuel consumption. The high RPM lobe actuates the follower. But since the follower isn't connected to anything, it doesn't cause anything to happen. This procss is illustrated by the figure to the right.

At high RPMs, oil pressure pushes a metal pin through the valve rockers and the follower, effectively binding the three pieces into one. And since the high RPM lobe pushes out further than the low RPM lobes, the two valve rockers now follow the the profile of the high RPM lobe. The high RPM lobe's profile is designed to open the valves open wider, and for a longer duration of time, thus allowing more fuel/air mixture to enter the cylinder. The improved breathing allows the engine to sustain its torque output as RPM rises, thus resulting in higher power output



That is basically how VTEC works. The picture to the right is a picture of an actual DOHC VTEC engine. Note that there are two cam shafts, one for the intake valves and one for the exhaust valves. For each pair of valves, notice that there are three cam lobes: two cam lobes on the outside, and one cam lobe in the middle.

As I've said before. The VTEC mechanism is nothing spectacular. DOHC VTEC is the most ambitious of all VTEC varieties in terms of specific output (except for the up coming VTEC-i). Yet as you can see, the implementation is elegantly simple. VTEC is Honda's solution to the design goal of improving engine breathing at high RPMs while retaining smooth and economical operation at low RPMs. DOHC VTEC technology is currently used in the 160HP Civic Si, 170HP Integra GS-R, 195HP Integra Type-R, 200HP Prelude base/Type-SH, 240HP S2000 and the venerable 290HP Acura NSX. And these are just the US-spec cars. Saying that VTEC is a successful design is an understatement.

After the sucess of DOHC VTEC engines, Honda became increasingly confident with the use of VTEC technology. It has proven to be a reliable and economical alternative to increasing displacement or using forced induction. Honda decided to apply VTEC technology to a larger segment of the market with the introduction of the SOHC VTEC system. Like its DOHC counterpart, SOHC VTEC optimizes the flow of fuel/air mixture for high RPM operation while maintaining smooth and economical low RPM operation. But due to its simpler design and humbler performance intentions, its specific output is not as high DOHC VTEC engines.

In a SOHC engine, there is a single camshaft per bank of cylinders. So both the exhaust and intake cam lobes are on the same camshaft. The figure to the right illustrates this design. The three cam lobes in the middle are the intake cam lobes. The two low RPM lobes actuate two valve rockers, which in turn pushes the intake valves open. The high RPM lobe actuates a follower, which is shaped like a valve rocker, but doesn't actuate any valves. While there are different intake cam lobes for high and low RPM operation, the same two exhaust cam lobes are used for all RPMs. The lack of cam profile changing for exhaust valves is the primary difference between DOHC VTEC and SOHC VTEC engines. Since the exhaust valves in a SOHC VTEC engine behaves just like a non VTEC engine, only the intake valves will be discussed below.



During low RPM operations, the two outer intake cam lobes directly actuates the two valve rockers. These low PRM intake lobes are optimized for smooth operation and low fuel consumption. The high RPM intake lobe actuates the follower. But since the follower isn't connected to anything, it doesn't cause anything to happen. This procss is illustrated by the figure to the right.



At high RPMs, oil pressure pushes a metal pin through the valve rockers and the follower, effectively binding the three pieces into one. And since the high RPM lobe pushes out further than the low RPM lobes, the two valve rockers now follow the the profile of the high RPM lobe. The high RPM lobe's profile is designed to open the valves open wider, and for a longer duration of time, thus allowing more fuel/air mixture to enter the cylinder. The improved breathing allows the engine to sustain its torque output as RPM rises, thus resulting in higher power output

The SOHC VTEC is a system that achieves mild power gains. Usually, SOHC VTEC engines gives about as much power as DOHC non-VTEC engines of similar displacement. Whether or not the added complexity of the VTEC mechanism off-sets the simplicity of SOHC (versus DOHC) is up for debate. SOHC VTEC is currently found on the Civic EX, Accord LX/EX/V6, Odyssey LX/EX, Acura TL, CL, and CL Type-S.

VTEC-E is a twist on the regular VTEC mechanism. Whereas VTEC's purpose can be more or less summarized as: extracting high RPM performance while maintaining smooth low RPM operation, VTEC-E can be summarized as: allow extremely lean fuel-air mixture at low RPMs in order to increase fuel economy. In other words, VTEC technology is used to optimize different ends of the RPM range in the two different implementations

First, some background information. Fuel is mixed with air and then combusted in cylinders to make torque. How much torque is generated is affected directly by how much and how well the fuel and air are mixed together. Less fuel and more air is called a "lean" mixture, the opposite is called a "rich" mixture. For low RPMs, a normal engine's intake charge velocity is low enough that the fuel and air are not mixed together very well. To make up for the sub-optimal mixing effect, a slightly rich fuel/air mixture (more fuel) is needed to maintain smooth operation. VTEC-E artificially increases the intake charge velocity, which creates a swirling effect inside the cylinder. This promotes a very good mixture of the fuel and air, thus allowing a lean fuel/air mixture to be used. The result of this is great fuel economy when running at low RPMs. Indeed, the current Civic HX, a 2400lb coupe, is capable of 37cty/44hwy fuel economy from a 115hp 1.6L VTEC-E engine. Now lets see how VTEC-E works in detail.

Unlike regular VTEC mechanisms, there aren't any extra cam lobes in a VTEC-E engine. So each pair of valves works off of exactly two cam lobes. Since VTEC-E merely increases the low RPM intake charge velocity, it is a mechanism that only affects the operation of the intake valves. VTEC-E is found only in SOHC engines due to its economical intentions. All this means that we only have to look at the two intake cam lobes and the associated rocker arms and valves in order to gain a full understanding of VTEC-E.

A non-VTEC-E engine normally has one single cam profile for the intake valves. A VTEC-E engine has two different intake cam profiles. At low RPMs, each intake valve works from its own intake cam profile. One of the intake cam profiles is very normal looking. The other one, however, is almost perfectly round, with just enough profile to it so that it pushes the valve open just enough to avoid pooling of fuel above the valve lip. Therefore at low RPM, only one intake valve is opening and closing. Most of the intake fuel and air are squeezed through this one valve, resulting in a good swirling effect in the cylinder. The swirling effect optimizes the fuel/air mixture, thus allowing a very lean mixture to be used.

As the RPMs increase, the demand for more fuel/air rises as well. Once a certain RPM is reached (approximately 2500RPM for the Civic HX), the one-intake-valve configuration starts to become a significant intake restriction. At this time, a solid pin is pushed through the two intake valve rocker arms, thus binding the two rocker arms into a single unit. This causes both intake valves to open and close according to the normal cam profile, while the almost-round cam profile is no longer used.

VTEC-E is some times confused to be just another high-RPM optimizing mechanism like other VTEC variants. And there is some truth to this: since only one intake valve is used at low RPMs, the one normal cam lobe is made to open that one valve slightly taller and for longer duration than if both intake valves are used. At higher RPMs, both valves follow this same cam lobe so they are both opened slightly taller and for longer duration. This results in a slight improvement in high RPM breathing compared to non-VTEC-E engines and thus slightly more power. This is evident by comparing the Civic DX and Civic HX engine. The two engines are essentially the same except for the VTEC-E in the Civic HX. But the Civic HX's VTEC-E mechanism results in 115hp, versus 106hp from the Civic DX. So the Civic HX has more power in addition to better fuel economy. But make no mistake, VTEC-E is designed with economy as the primary goal, not power output.

All the work Honda has done on the VTEC mechanism are combined to make the 3-Stage VTEC system. It is not a rumor, the engine exists: D15B. The engine is used in Honda Civics in Europe and Japan. In short, it combines VTEC-E and SOHC VTEC to get both extraordinarily good RPM fuel economy, and excellent high RPM power. The D15B is a 1.5L engine that is capable of about 54mpg and is rated for about 128HP. There is no other engine that can boast such combination of good fuel economy and power output. To understand how it works, it is recommended that the reader becomes familiar with the DOHC VTEC, SOHC VTEC, and SOHC VTEC-E mechanisms. This article assumes as such.



Looking at Stage 1 above, we see that both intake valve rockers operate independently. And at this low RPM, only one intake valve opens and closes since the other intake valve follows an almost-round cam profile. The almost-round cam profile is designed to open the valve just tall enough to avoid pooling of fuel above the valve. This mechanism is just like the low-RPM operation of the VTEC-E mechanism, resulting in great low-RPM fuel economy.

Stage 2 in the illustration shows the mid-RPM range operation. Starting at about 2500 RPM, the first oil pressure is applied, pusing a pin to lock the two intake valve rocker arms together. Both valves now follow the same low RPM cam profile in their operation. Thus far the operation has just been like a normal VTEC-E mechanism.

In Stage 2 above, the second oil pressure is applied at about 4500 RPM. The second oil pressure pushes another pin through the valve rocker arms and a cam follower that is between the two valve rocker arms. The cam follower operates from the high RPM cam lobe so now both intake valves follow the high RPM cam profile. This is like the high RPM section of an SOHC VTEC engine.

As seen from the power curve graph, each of the three stages has a distinct curve. And by choosing the switch-over points correctly, the optimal portions for the three stages can be combined into one curve. This level of low and high RPM optimization is unavailable from any other mass produced commercial engine.

It seems that combination of VTEC technologies is where the future lies for Honda engines. Already we are seeing this in mass produced US-spec Hondas: the J30A1 V6 used in Honda Accord V6s has a hybrid VTEC-E and SOHC VTEC system, though not a three-stage system like above. In this system, Stage 2 is not implemented. Only Stage 1 and Stage 3 are used: one intake valves open at low RPM, both intake valves open taller and for longer duration at high RPM.

ca va pouvoir en aider une couple qui dise encore v-tech ou vtek ou vtech

VTEC colise lol

Honda's use of the VTEC technology has lead to some pretty impressive achivements. This results in three camps of people: those that think VTEC is nothing but hype, those that know what VTEC is in terms of its benefits and limitations, and finally, those that think VTEC is the best thing to happen to automobiles since round wheels. Inevitably, misconceptions about VTEC are formed and thrown around. Much of the arguments on such forums as rec.autos.makers.honda is caused by such misconceptions. Here are some rather common ones:


DOHC VTEC engines have low crank torque compared to non VTEC engines of similar power output, and crank torque alone is an important indication of how well an engine will accelerate a car. Therefore the VTEC engine's power rating is not "real".
An engine's crank torque is directly related to how much fuel/air is combusted per engine cycle. For normally aspirated engines, this means that increasing the displacement size will usually result in increased crank torque. For forced induction engines, the effective displacement is larger than the numerical displacement since the air is pre-compressed before it is forced into the engine. Unlike increased displacement or forced induction, the VTEC system optimizes engine breathing at high RPMs to increase power. Therefore, a VTEC engine's displacement is the smallest of the three methods of increasing power output. And since crank torque is limited by displacement, a VTEC engine's crank torque output is smaller compared to non-VTEC engines of similar power output level.

But this doesn't mean that a VTEC engine's HP is somehow worth less. In fact, Honda automobiles equipped with VTEC engines have performance numbers that agrees with the tried and true power-to-weight-ratio method of estimating acceleration performance. People hold this misconception because they have a fundamental lack of understanding of the relationship between crank torque, horse power, and acceleration. Crank torque by itself is meaningless in determining the engine's ability to accelerate the car. This is because the crank torque is multiplied by the gearing and final drive ratio before it is converted to forward thrust. And physics dictates that an engine putting out 160HP absolutely will provide more forward thrust than a 150HP engine, regardless of what crank torque the two engines have, assuming similar transmission efficiency and optimal gearing for both cars. This is plain high school physics. Unless someone can prove that the laws of thermodynamics and Newtonian physics are false, there is no way around this fact.

There is some significance to the shape of the crank torque curve, however. When drag racing a car, it is desired to have a bit of initial wheel spin, and then have the tire hook up with the ground. A torque curve with a peak early in the RPM range and then tapers off as RPMs rise is well suited to this purpose. This is why big displacement American muscle cars are so good at drag racing. VTEC engines, on the other hand, have very smooth gradually rising torque curves. The initial wheel spin, therefore, is harder to achive. And after the initial wheel spin gets going, the level torque curve means that very precise clutch and gas pedal control is needed to allow the drive wheels to regain traction while maintaining maximum acceleration. This is why VTEC engines are more difficult to launch off the line than large displacement muscle car engines.


VTEC only works in high RPMs, therefore a VTEC car is just like a non-VTEC car at low RPMs. And since most people drive at low RPMs most of the time, VTEC is a waste of money.

quelqu'un viens de finir une recherche sur le systeme vtec ?

no I just found a great link and wanted to share
if that is seen as research ... well ... i guess it can be
personally I did not know the exact differences between 1st gen vtec and the newer versions

95EXRv6 said:

no I just found a great link and wanted to share
if that is seen as research ... well ... i guess it can be
personally I did not know the exact differences between 1st gen vtec and the newer versions

Click to expand...

yeah, it clears thing up once and for all

*tu*
good find

where's I-VTEC??

Technology : What is VTEC and how does it work?
Originally from honda-forum.com
VTEC is an acronym for Variable valve Timing and lift Electronic Control. It is a mechanism for optimizing air/fuel mixture flow through the engine.Honda first introduced the DOHC VTEC mechanism in the US on the 1990 Acura NSX. But a year earlier in 1989, the Japan Domestic Market got the world's first dose of DOHC VTEC in the 1989-1993 generation of the Honda Integra. The 1989 DA6 Honda Integra RSi/XSi used a 160hp variant of the B16A DOHC VTEC engine

VTEC, as most of us know, was a way to attack the compromise of low end power vs. high end power. It was pretty much impossible to make an engine with high output in the upper RPM range without sacrificing drivability in the lower RPM range. The physics of it work in a way such that a slower moving engine cycle responds better to low lifting valves with almost no overlap. However as the engine cycle speeds up and demand for air increases, the engine will need higher lifting valves with more overlap to meet the demand. If you have high lift/overlapping valves at slow engine speed, the engine won't be able to expel waste gases fast enough before it breathes in again. So instead of the nice breath of combustible oxygen air your engine was expecting to get, it gets a load of its already burnt carbon monoxide gas. You'll notice this happening with a loss in low end torque as well as shaking, sputtering, and crackling when the engine is at idle.

On the other side, if you run low lift valves you'll get your nice idle and smooth response in the beginning. However as the engine spins faster, it can't circulate the air quick enough and the valves end up closing before the engine has completed breathing in all the air it needed. You'll notice this when your engine is pushed harder, and your acceleration seems to get weaker rather than stronger.

Every camshaft has a rotation per minute which is perfectly matched with the cam lobe profile. You can usually tell how a cam was designed by looking at where the engine's torque peak occurs. The solution to that was to change the valve lift and timing on the fly, giving the driver excellent response at both ends of the RPM spectrum. Honda's solution was VTEC. An acronym that loosely stands for Variable valve Timing and lift with Electronic Control.

There were a couple ways that Honda implemented VTEC, most of them actually for fuel economy believe it or not. There are currently five different types of VTEC motors on the market. First is the DOHC VTEC. Then there is the SOHC VTEC or just VTEC. There is also a VTEC-E which has no performance value; it is used to for economy purposes only. The 3-Stage VTEC has three different stages that is used throughout the RPM band. And the new I-VTEC found in the K series which is just a little more advanced version of the DOHC VTEC.

So how does VTEC work? Well inside a pair of valves there are three cam lobes. The two outside ones are for lower RPM’s and the middle one works at higher RPM’s. As the cams spin around, the valves are pushed into the open position and air is let into the combustion chamber. The center cam lobe serves no purpose at low RPM’s and just spins along with the camshaft. This is pretty much the normal operation of the valve train, and this cycle will continue until it is directed to do otherwise. In order for the ECU to initiate the VTEC system, 5 engine conditions must be met:

Temperature: The engine must have reached normal operating temperature.

Throttle Position: The throttle must be open far enough to allow for increased airflow in

VTEC.

Vehicle Speed: The car must be in motion (wheels spinning).

RPM: Engine must spin to its target value. A GS-R for example starts at 4400 RPM’s.

Oil Pressure: The engine must be operating with normal and safe levels of oil pressure

determined by the VTEC pressure switch.

The ECU will send a signal for a spool valve to open. When this valve opens, oil is allowed into the pivot shaft inside the valve rockers and directed into the center rocker. Inside the center rocker, a set of pins are forced outward by the oil pressure and lock inside the rockers to both sides. This entire process occurs in 1/10 of a second. The valve rockers are now locked together and when the cams spin back around, the valves will be actuated by the single lobe in the center rather than being individually actuated by the smaller lobes. This will cause the valves to have an increase in lift and their duration has been increased allowing more air into the valve and successfully altering the valve timing.

Once the engine decelerates, the oil pressure holding the pins outward will be cut off and a return spring will pull the pins back into the center rocker where they will lay in wait for the next trip into VTEC. The smaller cams will then take over and the engine will return to normal operation.

The GS-R’s DOHC VTEC has a unique VTEC with its dual stage intake. It has two intake runners for each cylinder; one is longer then the other. Under 5800 RPM’s the longer runner is used. Above 5800 RPM’s a butterfly valve in the bore of the short runner opens to allow the passage of additional air to the cylinder. This boost mid and high-end power output. So the GS-R has a 3-stage operation of VTEC which works like this:


Stage 1 (0-4400 RPM): Low-lift cam lobe and long intake runners.

Stage 2 (4400-5800 RPM): High-lift cam lobe and long intake runners.

Stage 3 (5800+ RPM): High-lift cam lobe and short intake runners.

This three stage system is how the GS-R is able to keep a flat torque curve. Changing to a single-stage intake manifold such as the Eddlebrock or Skunk2 would change the motor to a normal DOHC VTEC that is similar to the Type R.

Most people confuse the opening of the short intake runners as VTEC engagement because of the dramatic change in sound. It is hard to hear VTEC at 4400 RPM using the dual-stage intake manifold because the long runners restrict flow volume to the engine in order to maintain flow velocity. So for anyone that says VTEC on their GS-R is engaging at 5800 RPM tell them their ears are not engine tuning devices.

Written by Cory (KenDawg13)

Thank you for the post. After so many questions and false thinking.


Just a note: Almost all manufacturers in 2004 have "VTEC"-style technology in their engine lineup (technology similar to VTEC in many aspects): Toyota (VVTI), Nissan, BMW (VANOS), Audi, Ford, etc etc. This technology is not unique to Honda anymore as some may think; some are pushing the technology more than that, some are pushing the R&D on different aspects (Honda is pushing research on the variable lift of the valves for example). Marketing wise, Honda decided to make huge emphasis on VTEC to make it a key-selling point, exactly like Subaru does with AWD (Traction Intégrale) for example. While AWD systems are common, Subaru make it a first order key-selling point in its offering ; Honda does the same with VTEC. Marketing wise, it's excellent, and they have succeded.

yes chuck is right about the Vtec, it's just a lot more spoken of then the other technologies ...

Vtec is the same or similar to zetec / duratec / mivec / vvti / powertech / vanos

I already had an idea of how VTEC worked, but the information posted as well as the images reinforced my understanding.
Thanks 95EXRv6 for sharing your find.

Chuck-S4 said:

Thank you for the post. After so many questions and false thinking.


Just a note: Almost all manufacturers in 2004 have "VTEC"-style technology in their engine lineup (technology similar to VTEC in many aspects): Toyota (VVTI), Nissan, BMW (VANOS), Audi, Ford, etc etc. This technology is not unique to Honda anymore as some may think; some are pushing the technology more than that, some are pushing the R&D on different aspects (Honda is pushing research on the variable lift of the valves for example). Marketing wise, Honda decided to make huge emphasis on VTEC to make it a key-selling point, exactly like Subaru does with AWD (Traction Intégrale) for example. While AWD systems are common, Subaru make it a first order key-selling point in its offering ; Honda does the same with VTEC. Marketing wise, it's excellent, and they have succeded.

Click to expand...

Neither vanos nor VVTI has dual cam profiles. Just cariable vavle timming, where as i-VTEC on the k20A have both. I do now know about nissan.

What about I-VTEC????

I didnty see anything on youre thread

from jim kerr
I-VTEC


Honda technology is always at the cutting edge: designed, refined, implemented, and produced to perfection. The latest Honda technology to hit the streets is actually an improvement on their VTEC (Variable valve Timing and lift Electronic Control) engine technology. They call it i-VTEC (the i is for intelligent) and Honda presented it to the Technology panel of the Automobile Journalists Association of Canada at their annual Car of the Year testing as a candidate for the year's "Best New Technology".




Currently i-VTEC technology is available on two Honda products; the 2002 Honda CRV and the 2002 Acura RSX. Two complimenting systems are part of the i-VTEC system. Variable valve lift is accomplished by using two rocker arms and different camshaft profiles to change the opening of the valve. The other technology is a computer controlled variable camshaft actuator that can vary a camshaft up to 50 degrees relative to crankshaft angle. Let's look at each in a little more detail.

Varying the camshaft in relation to the crankshaft is done with engine oil pressure acting on an actuator located on the end of the intake camshaft. The computer varies the oil pressure to change the rotation of the camshaft on its drive sprocket. This changes the valve overlap. Valve overlap is the amount of time both the intake and exhaust valves are open at the same time. Retarding the camshaft decreases the amount of overlap, while advancing the camshaft increases overlap.

Valve overlap plays an important part in engine operating characteristics. Very little overlap gives the engine a smooth idle and good slow speed torque, but it hinders high rpm engine performance. A large amount of overlap allows excellent engine breathing at high rpm but causes a rough idle and poor performance at low rpm. By varying the camshaft rotation and amount of overlap, the engine can have excellent performance at both low and high speeds.

Variable valve lift is accomplished by opening the valves with two different rocker arms and camshaft lobes. In the past, Honda operated VTEC engines with three rocker arms: two to open the two intake valves and a third that could be locked to the other two causing them to follow a different camshaft profile. With the new "two rocker" design, only one valve is opened at lower engine speeds. This causes the intake air fuel mixture to swirl, optimizing combustion at lower engine speeds. At a rpm programmed into the engine computer, oil pressure is used to lock the two rocker arms together. Now both valves open together but follow the higher camshaft profile the second rocker arm follows.

On the Honda CRV and 160 hp Acura RSX, only the intake valves are operated using this system. On the 200 hp Acura RSX Type S, both the intake and exhaust valves use this technology. Like the VTEC system first introduced on the NSX, this operation of both intake and exhaust valves provide maximum horsepower and torque.

Increased performance is one advantage of the i-VTEC system. The torque curve is "flatter" and does not exhibit any dips in torque that previous VTEC engines had without variable camshaft timing. Horsepower output is up, but so is fuel economy. Optimizing combustion with high swirl induction makes these engines even more efficient.

Finally, one unnoticed but major advantage of i-VTEC is the reduction in engine emissions. High swirl intake and better combustion allows more precise air-fuel ratio control. This results in substantially reduced emissions, particularly NOx. Variable control of camshaft timing has allowed Honda to eliminate the EGR system. Exhaust gases are now retained in the cylinder when necessary by changing camshaft timing. This also reduces emissions without hindering performance.

Currently, the Honda CRV and Acura RSX models are the only 2002 models on sale in Canada that meet Tier 2 emission standards which come into effect in 2004. Honda's i-VTEC technology gives us the best in vehicle performance. Fuel economy is increased, emissions are reduced, driveability is enhanced, and power is improved. It is a good possibility to win AJAC's "Best New Technology".


Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

more - article for CTR UK SPEC

Why Honda i-VTEC Conversion?

The Honda engine gives us more of what we love as sports car enthusiasts.

The advantages are increased horse power and reliability over 200HP. This together with a standard 6 speed close ratio gearbox clinches the deal.

Japanese specification engines also include a limited slip differential as standard.

The Honda i-VTEC as distinct from the earlier VTEC engine gives us much smoother power delivery with the i-VTEC system varying the duration of the intake cam by as much as 50 degrees continually, throughout the entire rev range, to produce a much smoother, controlled power delivery, as well as making substantially greater low and midrange RPM torque than the old VTEC system. i-VTEC is the cutting edge of engine technology today.

Producing 130 HP per litre at 7500 RPM is an achievement no other car manufacturer has attained.

thanks for all great info *tu*