What is VTEC?

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User - 07 Jan 2006 18:41 GMT

Yeah, I know it's some sort of variable valve timing. But exactly
what is it as implemented in my 2006 Civic LX? I've done a lot of
searching on the web, but I can't find my answers.

When does it activate? Is it a smooth, continuous action, or is it a
step change in configuration at some engine speed? Is it somehow
changing the fulcrums of the rocker arms? Is it rotating cam lobes on
the cam shafts? Is it rotating the cam shaft relative to the pully
driven by the timing belt? Is it selecing different cam lobes? Is it
a change of the valve lift? Opening only? Closing only? Is its
activation a function of engine speed only, or load, throttle
position, airflow, etc.? Is it done with solenoids in the head, or is
oil pressure used?

Any pointers to detailed engineering descriptions would be greatly
appreciated.

Thanks.

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Gordon McGrew - 07 Jan 2006 19:37 GMT

>Yeah, I know it's some sort of variable valve timing. But exactly
>what is it as implemented in my 2006 Civic LX? I've done a lot of
>searching on the web, but I can't find my answers.
>
>When does it activate?

Generally above a certain rpm which might vary slightly depending on
load - computer decides.

> Is it a smooth, continuous action, or is it a
>step change in configuration at some engine speed?

You won't be able to detect the transition. At most a slight change
in engine sound.

> Is it somehow
>changing the fulcrums of the rocker arms?

no.

> Is it rotating cam lobes on
>the cam shafts?

> Is it rotating the cam shaft relative to the pully
>driven by the timing belt?

> Is it selecing different cam lobes?

yes

> Is it a change of the valve lift?

yes

>Opening only? Closing only?

An entirely different cam profile is engaged. How that actually
varies the valve operation may be different from model to model.

> Is its activation a function of engine speed only, or load, throttle
>position, airflow, etc.?

Not sure of all the factors, but primarily rpm.

>Is it done with solenoids in the head, or is
>oil pressure used?

Solenoids (I think) redirect oil pressure which drives a pin to lock
cam followers together. When locked, the valves follow the profile of
the most aggressive cam which, at other times, is unconnected to the
valves.

>Any pointers to detailed engineering descriptions would be greatly
>appreciated.
>
>Thanks.

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Elmo P. Shagnasty - 07 Jan 2006 20:14 GMT

> You won't be able to detect the transition. At most a slight change
> in engine sound.

Maybe with the VTEC that's in the new engines, but in my 92 Si and my 02
Odyssey? You can tell. Man, in the Odyssey, when VTEC comes on, it's
F1 time.

That van has way more than 240hp. Honda just hates to admit it. That's
the only explanation for that van's performance.

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Gordon McGrew - 08 Jan 2006 00:38 GMT

>> You won't be able to detect the transition. At most a slight change
>> in engine sound.
[quoted text clipped - 5 lines]
>That van has way more than 240hp. Honda just hates to admit it. That's
>the only explanation for that van's performance.

I have a '94 GS-R. I can hear the engine change timbre at a certain
point but I understand that is due to a switch over in intake runners.
Otherwise, I couldn't pinpoint any change. In other words, Jeckle
does turn into Hyde but I cant say exactly when.

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TeGGeR® - 07 Jan 2006 20:00 GMT

> Yeah, I know it's some sort of variable valve timing. But exactly
> what is it as implemented in my 2006 Civic LX? I've done a lot of
> searching on the web, but I can't find my answers.

<snip>

> Any pointers to detailed engineering descriptions would be greatly
> appreciated.

The best one?
http://www.leecao.com/honda/vtec/index.html

And a very useful pointer indeed is here:
www.google.com
Type in thgese search terms exactly (including the quotes):
"how vtec works"

Two that came up when I did just that:
http://honda_fans.tripod.com/vtec-info.html (has cool animation)
and my own page:
http://www.tegger.com/hondafaq/vtec.html

Signature

TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

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Me - 07 Jan 2006 22:15 GMT

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

Not too complicated is it!

VTEC 10 years ago and today is the same. Only slight adjustments to improve
power or feul consumption have been made since. But the basic are the same.

> Yeah, I know it's some sort of variable valve timing. But exactly
> what is it as implemented in my 2006 Civic LX? I've done a lot of
[quoted text clipped - 14 lines]
>
> Thanks.

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Elmo P. Shagnasty - 07 Jan 2006 23:16 GMT

> VTEC 10 years ago and today is the same.

Not *quite*.

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Me - 08 Jan 2006 12:25 GMT

VTEC 10 years ago and now is the same principle or it would not be called
VTEC. Only adjustments to the VTEC configuration make either improvement in
performance or feul economy. As an example, the VTEC-E. Same priniple but
the setting are differenent. VTEC kicks in at 2500 RPM. You don't feel it
when it does kick in.
I don't know how a VTEC back then could be different from today.

>> VTEC 10 years ago and today is the same.
>
> Not *quite*.

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