The reason I am posting this is becuase I tired of noobs asking what is VTEC, and How does it work?

http://auto.howstuffworks.com/question229.htm

and also



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.

 

good stuff. a much needed post. hopefully no more "when vtech kicks in ... !"

 

Lol

 

Please add stuff if you like

 

Pros and Cons of VTEC

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.

 

By the way VTEC stands for Variable Valve Timing and Lift Electronic Control

 

economic daily driver/weekend racer: dohc vtec = good

grocery-getter: sohc vtec = good

street/drag/autox = some hot cams, no vtec!!


i just hate seeing people who think vtec its like having a turbo or something.. when its more of an economy thing than power-booster..

 

Lets please only post stuff about VTEC, not critizing it

 

And also economic? have you driven a VTEC car?

 

iv owned several.. and driven practically every vtec engine cept the nsx and rsx.

they are a balance of economy and power.. its not a high HP racing mechanism. if they were, you would see a bunch of 10 sec and faster cars with vtec/vvt-/mivec/ctvc on them.

i wasnt critisizing it. i think its awesome, i love it.