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Old 02-09-2007, 06:12 PM   #51
AREITU
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I think in the next few years, people will begin to realize the benefits of tuning with variable valve timing systems. EMS technology should eventually catch up, too. Power Enterprise even makes a CamCon device for VVTI.

Quote:
Originally Posted by grippgoat View Post
VTEC doesn't run two sets of actual camshafts, but that's silly. I'm sure it's not literally what he meant.

For a pair of valves, the camshafts have a separate 3rd lobe between the two lobes that are normally there, and when VTEC activates, it does something funky I never quite understood to start making both valves follow the more agressive center lobe.

So while AVCS can change overlap and cam timing, VTEC can actually change lift and duration. Although I think some newer honda engines actually do both. They have variable cam timing like AVCS as well as the 2nd set of cam lobes that can be activated.

-Mike
There's about half a dozen versions of VTEC. SOHC and DOHC versions, and variations of both. All SOHC VTEC systems work only on the intake side. Basically, each intake cam lobe is staggered, one slightly smaller than the other, to promote swirl. Above a certain RPM, the VTEC solenoid pushes a pin through the rockers, which forces both valves to follow the larger lobe.

In DOHC VTEC, (Prelude, Integra GSR, S2000, Si, RSX-S etc) there is a 3rd lobe (high lift and duration) between the normal lobes, as if each cylinder had 3 valves. Below each lobe is a rocker, but the one under the high lift lobe floats freely before VTEC engagement, and the rockers follow the low-lift lobes. When VTEC engages, it opens a solenoid that pushes a a pin through all three rockers, forcing the valves to open with the biggest lobe: The high lift lobe.

here's an old article. http://asia.vtec.net/spfeature/vtecimpl/vtec1.html
And a picture: http://www.accordforum.de/images/vte...m/vtec_cam.gif

i-VTEC is simply cam phasing (Like AVCS) on top of VTEC.

With that OT stuff out of the way...

Is AVCS two-step, or is it infinitely variable within a given range?
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Old 04-14-2009, 01:40 AM   #52
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I have a pretty good understanding of both the AVCS and the Vtec in Hondas... however, the question I have is this: is the AVCS an instantaneous actuation (solenoid kicks at an rpm), or is it more gradual? The reason I ask is this... if a person were to put an AVCS engine into a WRX with a non-avcs computer, could you actuate the avsc with an rpm dependent switch much like a Vtec controller? I hear idle can be a real problem with an avsc engine in a non-avsc car...
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Old 04-14-2009, 02:06 AM   #53
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No, there's an engine load vs rpm table for how much timing advance to give the AVCS.
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Old 04-14-2009, 02:26 AM   #54
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The link doesn't work for me . Am i the only one having this problem?
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Old 04-14-2009, 09:02 AM   #55
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Quote:
Originally Posted by Godspeed55 View Post
The link doesn't work for me . Am i the only one having this problem?

Try this: http://www.drive.subaru.com/Win05_WhatsInside.htm

Seems they put an extra dot in at some point.
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Old 04-14-2009, 11:04 AM   #56
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Quote:
Originally Posted by STIBungy View Post
No, there's an engine load vs rpm table for how much timing advance to give the AVCS.
Ok... how about this... I know the advance is load specific, but we want the capability for sure. The issue is low end drivability. Why couldn't we just switch it at say 3k. It may not be as precise as the computer/load controlled switch, but it would give the basic desired results... low end grunt and open end breathing with no idle issues...

Any thoughts?????

BTW... the top length wasn't working for me either Godspeed....
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Old 04-14-2009, 11:16 AM   #57
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I've pondered this thought too , If it is possible to connect a micro switch to the throttle to activate the solenoids ?
Ideas anyone ?
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Old 04-15-2009, 09:56 AM   #58
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It appears to be a 2-wire solenoid, much like the vtec solenoid. Seems a switch, like a vtec controller, with a rpm input/trigger would be just the thing...
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Old 09-25-2009, 06:37 PM   #59
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Here, I am still a Toyota Celica GT-S owner and there is a wealth of information on how these systems function at Newcelica.org
http://www.newcelica.org/forums/show...1&referrerid=0
How Lift works (Toyota's approach toward this)
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Old 11-01-2010, 10:19 PM   #60
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that link is broken
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Old 11-01-2010, 11:23 PM   #61
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no kidding, this thread is almost 6 years old
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Old 11-02-2010, 09:47 AM   #62
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Looks like I posted on this wayyy back in 1/05.
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Old 11-02-2010, 10:13 AM   #63
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GOOD NEWS! It's a thread and people still read it so......fix or delete, eh?
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Old 11-02-2010, 10:56 AM   #64
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The link in post #55 works for me. Very good article. I .pdf ed it. If anyone wants an email just shoot me a pm.
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Old 11-02-2010, 11:09 AM   #65
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Quote:
Originally Posted by Smdavis27 View Post
Here, I am still a Toyota Celica GT-S owner and there is a wealth of information on how these systems function at Newcelica.org
http://www.newcelica.org/forums/show...1&referrerid=0
How Lift works (Toyota's approach toward this)
that's not really the same thing, vvti is closer to avcs
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Old 05-10-2011, 05:01 PM   #66
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i really wish i could read this article, any one have an alternative? or no where to find it?!
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Old 05-10-2011, 06:42 PM   #67
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AVCS allows continuously variable (not stepped, and not just one or two positions) changes of camshaft timing. Single AVCS is intake cam only, dual AVCS is both intake and exhaust cam. Many car companies have the ability to control cam timing in this way (pretty sure Nissan, Hyundai, and Ford do this on their 4 bangers). Subaru's implementation uses engine oil pressure driven into the cam sprocket to change the angle of the camshaft in relation to the teeth on the sprocket and timing belt. The engine oil flows through a PWM-driven solenoid with closed loop ECU control to ensure a specific requested camshaft angle is maintained during operation. I believe older implementations allow up to 30 degrees of camshaft advance (15 crank degrees), and newer ones may do up to 40/20. Not positive on that.

From there, all you need is just a good book on engine operation to understand what cam shaft timing is and its effects on engine operation, but here is a quick version:
"Optimal camshaft timing" is difference under different RPM and loads. Camshaft timing will affect volumetric efficiency, and/or better emissions, and/or fuel economy. If you do not have this camshaft control, camshaft timing is a tradeoff. Camshaft timing may allow good torque and acceptable emissions, but poor top end power. With a dynamic camshaft, you can get both.

There are still other camshaft elements that AVCS lacks in comparison to some competitors' systems. There is no control over the profile of the cam, so no changes in lift or duration are possible. Duration, lift, and shape are still tradeoffs, and it would be preferred (cost and reliability issues set aside) to also be able to control these if you are seeking optimal power, efficiency, emissions, etc.

Last edited by Freon; 05-10-2011 at 07:06 PM.
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Old 05-11-2011, 12:47 AM   #68
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What can my avcs system do for me? Is it dificult for a tuner to tune the avcs, I don't hear about it often
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Old 02-05-2013, 10:05 PM   #69
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Old 12-22-2015, 01:35 AM   #70
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Does anyone have an updated link to the AVCS article? I tried each link in the thread but they all come up broken.
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Old 12-23-2015, 01:37 PM   #71
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Old 04-21-2017, 09:08 AM   #72
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All the links are broken again.
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Old 04-23-2017, 11:50 AM   #73
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Great find good sir!
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Old 04-23-2017, 03:23 PM   #74
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Quote:
Originally Posted by grex07 View Post
All the links are broken again.
. I can also confirm ALL AVCS explanation links are broken and do not work.
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Old 11-05-2019, 11:45 AM   #75
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Thank you!
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