Yo, TECH HEADS - I need help writing an article..

[VTEC_boi]

I'm writing an article for my website's Tech Section (the very first article ) For newbies - it's explaining VTEC.

Now, I cannot remember the number of rocker arms! How many per lobe? Or what?

Thanks a lot!

and does anyone have a diagram or can u explain the third rocker arm? What does it do? I've never really understood the third rocker arm......
peace

[ric]

see if i can tell you briefly. basically when vtec engages the third rocker arm(center one) becomes connected via a bridging mechanism(pin) to the other two rocker arms making them follow the vtec lobe instead of the economy lobe. remember thats pretty basic

here are some articles to read

http://www.lathi.net/honda-faq/vtec.html

and another
http://www.nsxprime.com/FAQ/Technical/VTEC.htm

and another
http://www.magicnet.net/~joeg/turbo_mag/vtec.html

and another
http://www.teamdelsol.com/techstuff/vtec/vtec.htm

and another
http://www.importracer.net/articles/diffvtec.html

and another
http://asia.vtec.net/spfeature/vtecimpl/vtec1.html

hope that helps

[JD@af]

I don't ever think I've seen any good explanations for VTEC systems on the SOHC D series engines, but for DOHC B series engines, each cylinder has 6 total rocker arms (three intake, three exhaust), so 24 total. I think that VTEC H series engines use the same number of rocker arms, as do the K series i-VTEC engines (well, actually the K20A - base RSX - only uses one per valve, but the K20C - RSX S - uses three per each pair of valves, like the B series).

Also, you might find this brief run-down I wrote about VTEC helpful. Feel free to use it as you wish

Originally posted by JD@af http://www.automotiveforums.com/vbulletin/t599.html
There are tons and tons of good articles out there explaning this, but, I just can't find any right now. Besides, how much fun is it when you ask a question and are answered with a link? As if to say "read about it for yourself."

So, that being said, here is an abridged explanation of variable valve timing and its benefits:

This may be a little below your level, and if so, I apologize, and hope I do not sound as if I am patronizing you. The point of variable valve timing is to create overlap at high rpms, or periods of time at which both the intake and exhaust valves are open simultaneously. What this does is create a bit of a suction, as the pressure of the exhaust gases as they are exiting the cylinder leaves a low pressure area in the cylinder, that the open intake valve allows air to fill, and mix with gasoline. This extra air/fuel mixture naturally equals more power. So the purpose of variable valve timing is to draw in more air at higher rpms and create more power.

The follow-up question to this is why not use this variable valve timing at all rpms for more power? The answer here is that these characteristics work wonders for creating power at high rpms in naturally-aspirated motors, but they actually discourage power production at lower rpms. The overlap does not work well at engine speeds where the motor easily obtains the air it needs to make power. Variable valve timing is effective at drawing in air at those engine speeds where usually only forced induction will supply the air needed to make more power.

Beyond that, Honda's VTEC system uses cams that have three lobes for each pair of valves. The two outer lobes open and close the valves when VTEC is not engaged. Once the VTEC criteria are met (VTEC is controlled by five factors (which are escaping me right now), including rpms, coolant temperature, throttle application, and a couple others), a set of VTEC rocker arms lock in place, joining the retainers of both valves, so that both valves operate off the single, larger cam lobe in the middle. This cam lobe opens and closes the valves allowing for the overlap as described above.

In a nutshell, that's variable valve timing.

[texan]

The only difference on SOHC engines is that it's the intake valves that have three rocker arms per 2 valves (the exhaust uses the standard 1 arm per valve). There isn't enough room on the single cam to throw 6 lobes per cylinder on, so they simplify the system by using VTEC on the intake set only, hence 5 lobes per cylinder.

[sparq]

Originally posted by texan
There isn't enough room on the single cam to throw 6 lobes per cylinder on, so they simplify the system by using VTEC on the intake set only, hence 5 lobes per cylinder.

Hence why the SOHC VTEC motors SUCK

[VTEC_boi]

Thanks a lot guys! (JD@af - I'll quote u on that hehehe)

I thought I knew a lot about VTEC - but there's always something to be learned

Thanks again!

[JD@af]

Here’s one you all can help me with, while we’re on the subject. My GS-R, from what I’ve read, has two stages of “VTEC” (though I don’t think the first stage is truly VTEC at all). These are the dual-stage intake manifold runners, which switch from the long runners to the short runners once you hit 4,400 rpms. The second stage, which hits at 5,800 rpms, is the initiation of VTEC, as described above. While the change in engine tone is a little difficult to detect with OEM I/H/E, with aftermarket units in place, the change in tone is quite a bit more pronounced. Now, the stage is set for my question:

Why is it, now that I have a primitive JRSC with JRSC manifold on the intake side, which does not have paired long and short runners, that I can still hear a change in engine tone at 4,400 rpms?

[texan]

You've got that one backwards JD. The VTEC selenoid locks the thrid rocker arm into action at 4400 RPM, the secondary intake runners open at 5800 RPM. There is only one stage of VTEC, the secondary intake runners are a different technology entirely. Also, the secondary intake runner butterflies just open a second, shorter set of runners, they don't close the lower RPM long runners.

You can still hear an audible change in engine note because a significant change in valve event timing causes a significant change in the dynamics of airflow through the motor.