How Vtec works, Little video I found

Just a little video I found on streetfire on how the system actually works.


http://videos.streetfire.net/video/DDD9096...752F982ED3A.htm

Might be easier to grasp when it is shown in a movie

That's a great lil video. I've seen a lot of them for almost every internal engine thingy but this is the first I've seen for vtec. Always fun to watch.

anybody else still confused? haha

Just wondering how come VTEC must activate the last 2K rpm before red. What happen if VTEC start kick in from 2.5~3K rpm like turbo do?

btw, thanks for the video

Nice. I am saving that link.

That is a fascinating video... but now I am confused! I thought the two small lobes were used for "normal" and the large middle lobe was used for VTEC?

That video shows all lobes working before VTEC, just the sequence is gradual. The VTEC then just has all valves opening at the same time. If the video is true then VTEC and non VTEC would have the same lift, which is not true???

Valve timing that is optomized for high RPM operation doesn't work well at lower revs. You could modify the motor to run on the high RPM cam profile ("VTEC") all the time if you wanted to (though for it to work at all you'd need a stand alone ECU), but all you'd get is a lumpy idle, very little torque at lower revs, and poor gas mileage. You'd still have the same power above 6k, but you'd pay for it big time at lower revs and at idle.

VTEC allows a mild profle and staggered valve timing for excellent performance at lower revs and a change to a higher lift longer duration timing without the stagger for greater peak power at higher revs. It actually makes more sense to look at VTEC as a way of giving a high strung engine a decent idle and low end torque, because it actually does nothing to increase performance. The high lift cam profiles will deliver exactly the same power with or without VTEC.

The center rocker arm always rides on the center cam lobe, so it always goes up and down, but it isn't connected to the rockers that open and close the valves until the VTEC pins slide into place and lock all three rockers together.

If that's not clear, read on and I'll try to explain it a little more fully.

Below VTEC each valve is controlled by a single rocker arm. Note that in the video you can see how the two valves open and close at slightly different times. The center rocker also rides up and down on its cam lobe, but it is not connected to the two rockers that open and close the valves. It just moves up and down without doing any real work. Then, when the VTEC pins are pushed through the rockers (by oil pressure) all three of the rocker arms are locked together. Now the two arms that open the valves have to follow the center rocker arm, which is following the hotter cam profile.

I hope that helps, but if it's not clear please feel free to ask more questions.

Another piece from "How stuff works.com"

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

figures...i go to click on the click and get 'page can not found'. looks like they're in the process of overhauling streetfire.net, so who knows when the video will be back up.

This post has been edited by vindaloo on Jun 15 2006, 05:08 AM

Seems to be working now vindaloo.

Thanks! I had to watch that at least 3 times just to understand what's going on. Those Honda engineers are pretty damn clever.

That was a great explanation. Thanks!

there's a better one floating around with commentary...when I get home if i remember I'll post it.