What's vtec for anyway?

[90redgt]

Alrighty, i'm just asking a serious question here so elighten me. I've never known what honda came up with vtec for so i'd like to know what is it's purpose? high rpm valvetrain stability? gas mileage? Just curious cause there's a lot of talk about, "vtec this" and "vtec that". (putting my flame suit on )

[Options]

VTEC = Variable Valve Timing and lift Electronic Control.

What it does is when a car hits vtec usually at about 5500 rpms or so it in away switches to using different lobes on the camshaft, making the duration and lift on the valves greater, increasing the amount of air you can put into each cylinder and their for increasing horsepower, in the top end.

Thats the basic of how vtec works and what it does.

[Blowncivic1320]

Originally Posted by Options

VTEC = Variable Valve Timing and lift Electronic Control.

What it does is when a car hits vtec usually at about 5500 rpms or so it in away switches to using different lobes on the camshaft, making the duration and lift on the valves greater, increasing the amount of air you can put into each cylinder and their for increasing horsepower, in the top end.

Thats the basic of how vtec works and what it does.

Thats only on the B-series engines. It does sumtin else on the D-series I forgot what that was tho (its a more primitive way then mentioned above.

[CivicSiRacer]

ON the D series engine where you only have one cam there are a set of lobes that only open up for the intake side.

But in reality VTEC, VANOS (BMW), VVTL-i (Toyota), and other companies that have this feature you get the best of both worlds.

Great fuel economy, and a little bit more power at the high end. That's why all these cars can rev so high. Notice the Hondas, Acuras, BMWs, and Toyotas all rev up past 7000-8000rpms.

[Dons92CivicVX]

Then there's the VTEC-E ("E" for economy). This is what I have in my 92 Civic VX.
I'm not a motor head by any stretch of the imagination, however, after some web surfing I've found that the Honda Civic with VTEC was first introduced in 1992 (USA & Canada). From what I've found, there are two different VTEC engines. The VTEC(D16Z6) and VTEC-E(D15Z1). The VTEC is equipped with multiple cam lobes per cylinder, providing one valve timing and valve lift profile at low speeds and a different profile at higher speeds. Switch-over from one profile to the other is controlled electronically, and is selected by monitoring current engine speed and load.
Unlike the typical VTEC whereby it kicks in at 5500 rpm's as suggested by Options, the VTEC-E kicks in at ~2000 to 2500 rpm's (it even has a gear shift indicator to assist in optimizing fuel efficiency).
Hope this helps.

Knowledge is key,
Jesus is King.

[Options]

Originally Posted by Blowncivic1320

Thats only on the B-series engines. It does sumtin else on the D-series I forgot what that was tho (its a more primitive way then mentioned above.

on SOHC motors vtec does the same thing but only on the intake side of things, it doesnt increase the lift and duration on the exhaust valves, it only does to the intake valves.

[loesch8102]

Ok, so how then with an SOHC does it benifit to allow more air in, but no more out? I would think that would create problems.

[Options]

Originally Posted by loesch8102

Ok, so how then with an SOHC does it benifit to allow more air in, but no more out? I would think that would create problems.

More air in allows you to put more fuel in, therefor you get greater combustion and better thermal expansion, And now if the exhaust valves werent at their flow capacity when the car is running under normal conditions when vtec kicks it just pushes more air out, faster.

Even if the exhaust valves are at capacity when it is at normal conditions, when vtec were to kick bernoulli's principle would take into effect, pushing the extra exhaust gas produced during the combustion cycle out.

[Tanked]

Since VTEC is really creating two powerbands (one for each lobe), doesn't it increase low-end and high-end power? Isn't it like having an engine optimized for both low and high speed?

[GZusREVolution]

Originally posted by Dons92CivicVX

Knowledge is key,
Jesus is King

[Options]

Originally Posted by Tanked

Since VTEC is really creating two powerbands (one for each lobe), doesn't it increase low-end and high-end power? Isn't it like having an engine optimized for both low and high speed?

Nope only for top end, it just uses normal lobes below 5500 rpm's

[boosted331]

Originally Posted by Tanked

Since VTEC is really creating two powerbands (one for each lobe), doesn't it increase low-end and high-end power? Isn't it like having an engine optimized for both low and high speed?

Hit the nail on the head. If you only had your vtec lobes you'd get a choppy idle and bad low end performance. If you only had your primary (non-vtec) lobes you'd get a smooth idle and good low and midrange, but it would die up top. So in a way, yes, vtec does add more low and high end power.

[xRiCeBoYx]

so, what's the difference between regular vtec and i-vtec (like in the '03 civic si)?

[Options]

Originally Posted by xRiCeBoYx

so, what's the difference between regular vtec and i-vtec (like in the '03 civic si)?

I have no idea my self i have heard its like a 3 stage vtec or something i really have no idea.