VTEC does it really do anything?

[toronto pimp]

And another thing, VTEC is shitty for drag racing. That's why some company called TODA makes this product called VTEC KILLERS (only for racing purposes) because you get power all the way through instead of just at 5500rpm+

[BLU CIVIC]

VTEC is somewhat highly over-rated when it comes to people telling their stories as to how their "V-TEK kicked in and i beat him by like 5 cars" itz just something that helps ur engine preform better in high rpms or if u have a VTEC controller, can have that help early on in the game instead of waiting...i guess u can call it a "performance enhancer"

[90civicracer]

Originally posted by 4g4d_getone
i think that the sohc vtec doesnt really do any thing but u can really feel it in a dohc motor.

I agree, I have a friend w/ a '99 Civic EX with only a muffler and short ram intake and i have beat him even though he has V-TEC (though be it only SOHC). I have also driven his car and once u hit vtec it isn't that noticable....however i do agree about the DOHC V-TEC like in B16's and B18's how it is much more noticable it actually is.

[toronto pimp]

VTEC is obviously gonna do alot more in a DOHC car with a more powerful engine. And if you had a 91 si hatch or whatever...you're car would be alot lighter and have no much less power then the ex's so nothing would suprise me there.

[90civicracer]

Originally posted by toronto pimp
VTEC is obviously gonna do alot more in a DOHC car with a more powerful engine. And if you had a 91 si hatch or whatever...you're car would be alot lighter and have no much less power then the ex's so nothing would suprise me there.

Well i dont have a 91 si hatch but i do have a 90 Civic EX which of course has the same engine as the SI's of that generation so you were close enough Right now it's being swapped out for a SOHC ZC though and will probably have it back by this Saturday (i can't wait, been almost a month since i've driven my car)

[DarkImportGrey]

sohc vtec isn't meant to be some high performance 8000rpm monster, it is meant to give the car extra power in situations like highway passing.

The same type of effect is achieved in trucks that use the Miller cycle instead of the standard Otto cycle.

In Europe there is a d15 sohc with three different stages of VTEC that makes 130 hp and gets 54 mpg.

[90civicracer]

I would love to see that combo of 130 hp and 50+ mpg considering my life as a 16 year old isnt filled with money to spare or rich parents to have pay for everything.

[jNYCe5]

Originally posted by DarkImportGrey
In Europe there is a d15 sohc with three different stages of VTEC that makes 130 hp and gets 54 mpg.

yup the d15b out of 92-95 civic vti's in japan... pretty bad ass lil motor, my friend had one in his crx before he went b20/vtec... there's a shop here in my town that sells them. Japanese Engines Inc. about 650-700 for the whole swap

[markd91civic]

Hey jNYCe5 Does this shop have a web site or a phone number where they can be reached.

I just bought a 91 Civic Dx 4dr with 266K and I need to do something with this motor.

Thanks,
Mark D

[Rufes1]

We need Setanta here

[l2ice rocketz]

Got a little bored. Here ya go. Enjoy!


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.


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.

*Edit*
Before all of you flame me for not writing this. I got this off howstufworks.com. ^_^

[toronto pimp]

i wouldnt mind having that engine for the mpg and extra performance

[95civicman]

Originally posted by Problem_Si
My bad, it was in Sentata's sig...here it is for your viewing pleasure...

yea that's it. i wasn't sayin it was like a turbo, just sayin that because it was funny.

[origamiguru]

Umm.... correct me if I'm wrong, but I do believe the i-VTEC engine currently in the Acura RSX (type-S) utilizes the three-lobe system that DarkImportGrey is speaking of.

Of course, that's my opinion, I could be wrong.

-Adam.

[DarkImportGrey]

the three lobe system in the euro d15 however is not the same system as the RSX type S head...

on the euro d15 that gets 54mpg, one of the cam lobes is almost perfectly round...