[narayan]

Originally Posted by WhiteKnight

Hey, don't be depressed!!! If you are a person who shifts up below 4500 rpm, I don't think VTEC matters to you. That's because VTEC kicks in above 4500 rpm (VTEC gurus...pls confirm).

I remember reading the ACI first drive for VTEC long time back. They were saying something like this- "If 1.5 is a wild stallion, the VTEC reminds one of a thoroughbred racehorse". So be happy that you don't own a donkey. the 1.5 is a great car.
IMO, please don't try putting VTEC log and fake twin exhaust etc. It looks very naive.

was just voicing my feelings !! would never put those puny twin pipes ( VTEC owners excuse pls !! )

[iraghava]

Originally Posted by Shan2nu

So the Vtec must be kicking in at around 3500-4000rpm. It wont affect FE as we hardly cross 3000rpm when we're in economy mode.

From my experience it does kick-in at about 3500-odd rpm, not at 5200.

[goldie_malhotra]

Originally Posted by iraghava

From my experience it does kick-in at about 3500-odd rpm, not at 5200.

From what I read somewhere, it kicks in at 2500 rpm at full throttle and at 3500 rpm at half-throttle for the OHC/NHC (VTEC-E types). Though my own gut feel/experience is upwards of 3000 rpm.

[v1p3r]

It activates at 4200 rpm and deactivates when you go below 3800 rpm.

[Mpower]

Originally Posted by mega5918

Mpower,
In deed the cam does move in few of the VTEC engines. In Few of the VTEC models they introduced 2 lobes close to each other on the same CAM so that they can lock the valves at higher RPM's and use a different lobe to operate the same set of valves not sure of the Engine type (DOHC or SOHC).

The camshaft probably slides in and out (along its axis) instead of the lobes sliding in and out, but what I am trying to say is that the cam does not move up and down in order to change valve lift.......and in the BMW system it does exactly that.

[arctic]

Originally Posted by Mpower

The camshaft probably slides in and out (along its axis) instead of the lobes sliding in and out, but what I am trying to say is that the cam does not move up and down in order to change valve lift.......and in the BMW system it does exactly that.

from what i heard one(of 2 inlet ) valve opens less at low rpm (not sure if its due to the cam sliding) and at higher rpm both valves are locked by some hydraulic pin thingee to open full, so im guessing the inlet lobes are of different size both working at low rpm and only one (high lift) lobe working at high rpm on both valves which are locked together with the pin...sliding cam=more moving parts=more murphys law can strike.

could someone verify???

[Pankaj401]

Originally Posted by v1p3r

It activates at 4200 rpm and deactivates when you go below 3800 rpm.

That's where I might have confused it with 5200rpm.

Connect a voltmeter to the VTEC Solenoid Switch and taking the car for a spin might give the correct result. Will try sometime soon.

[Mpower]

Ok so getting back to the topic, even though its only a 5 bhp difference, laying the 2 power curves on top of each other will show you the different nature of the 2 engines.

A sedate driver who drives slowly in city traffic might prefer the 1.5 and label the VTEC as being sluggish.

[Shan2nu]

This is the torque and power curve for the L15A Vtec engine (NHC Vtec?).

You can see that the torque increases till 2750rpm and then stabalises, then at 3500rpm, it begins to rise again. This is where the Vtec kicks in.

Shan2nu

[goldie_malhotra]

Originally Posted by Shan2nu

This is the torque and power curve for the L15A Vtec engine (NHC Vtec?).

You can see that the torque increases till 2750rpm and then stabalises, then at 3500rpm, it begins to rise again. This is where the Vtec kicks in.

Shan2nu

Yups - that is the one on the NHC Vtec.
More Details here - Temple of VTEC-Asia

[four_tire]

You can find the patent for the VTEC .. but its too much techie

Control system and method and engine control... - Google Patents

god bless .. if anbody can understand please summarize

[four_tire]

VTEC misconceptions

[FONT=Verdana,Arial,Helvetica]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.

[/FONT]

posted by Brain


picked this article from VTEC Tunerz

[four_tire]

[FONT=Verdana,Arial,Helvetica]DOHC VTEC

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.

SOHC VTEC

[/FONT][FONT=Verdana,Arial,Helvetica]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.

SOHC VTEC-E

[/FONT][FONT=Verdana,Arial,Helvetica]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.

3 STAGE VTEC

[/FONT][FONT=Verdana,Arial,Helvetica]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.



picked from VTEC Tunerz
[/FONT]

[Shan2nu]

@4tire

Instead of copy pasting the whole article, it would be better to post the first paragraph and then provide the link to the wbepage, for further reading.

Shan2nu

[chetanhanda]

Originally Posted by Pankaj401

In OHC VTEC the VTEC kicks in at 5200rpm.

whats the engine number in the OHC VTEC ? is it a D16 series .. ?