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Old 01-17-2005, 08:10 PM   #26
clamdip
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yes, AVCS only applies to intake cam timing, not exhaust cam timing. which is why there is valve overlap.
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Old 01-17-2005, 09:04 PM   #27
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All new Honda engines that have VTEC are called "i-VTEC" now. The i stands for "intelligent" because now not only is cam profile changed at the set RPM, but intake valve timing is adjusted throughout the whole RPM range as well. Just like AVCS but with camshaft profile change thrown into the mix which VTEC stands for. So basically "i" is Honda's "AVCS."
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Old 01-17-2005, 10:02 PM   #28
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yes, now VTEC is controlled by the ECU as well. you can totally feel the difference when driving both i-VTEC and VTEC cars. one of my friends has a JDM B16 honda engine and my other friend has a RSX-S. you can totally feel how the low-end is totally improved as opposed to previous years. add that along with a high compression ratio, and it's immediate response in every gear.

the only thing missing from AVCS is the cam profile change or LIFT as it's called.
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Old 01-17-2005, 11:03 PM   #29
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Correct. When will people get it thru their heads that AVCS does not alter LIFT?
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Old 01-18-2005, 12:27 AM   #30
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don't know. i remember i had this discussion once about AVCS and VTEC and people thought that it was exactly like VTEC. i was trying to get them to realize the difference, but they just weren't seeing that through my explaination. maybe it was a bit fuzzy to them i don't know. at least now, if they see this post they'll realize the difference. well, i guess that's what forums are for.

i remember riding in my brothers friends turboed CRX with a built GSR engine. that thing pulled like a bat out of hell once it hit like 6 grand. i think he clocked 11's high 10's with slicks on. it was pretty awesome.
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Old 01-18-2005, 10:47 AM   #31
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Quote:
Originally Posted by clamdip
yes, now VTEC is controlled by the ECU as well. you can totally feel the difference when driving both i-VTEC and VTEC cars. one of my friends has a JDM B16 honda engine and my other friend has a RSX-S. you can totally feel how the low-end is totally improved as opposed to previous years. add that along with a high compression ratio, and it's immediate response in every gear.

the only thing missing from AVCS is the cam profile change or LIFT as it's called.
If i'm not mistaken VTEC was always controlled by oil pressure through the ECU's signal. The reason why Apexi and other manufacturers make piggyback computers that can alter the VTEC engagement at any point in the RPM range. I used to have one so i'm familiar with the system. An apexi V-AFC and Honda Prelude VTEC
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Old 01-18-2005, 03:05 PM   #32
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Quote:
Originally Posted by gills
If i'm not mistaken VTEC was always controlled by oil pressure through the ECU's signal. The reason why Apexi and other manufacturers make piggyback computers that can alter the VTEC engagement at any point in the RPM range. I used to have one so i'm familiar with the system. An apexi V-AFC and Honda Prelude VTEC
correct, VTEC is a mechanical system which is regulated by oil pressure, however i-VTEC is controlled or regulated by the ECU on top of the mechanical system. so now, you wouldn't need a V-AFC or any piggyback EMS, so it's a lot more efficient than before in terms of fuel economy and power. in other words, it's like AVCS with variable cam profile or LIFT as we all love.
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Old 01-18-2005, 03:37 PM   #33
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So all those ricers and Honda fanboy's have been right all along.



(i-)VTEC is teh fAstar!!1!one!rice!!1!
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Old 01-18-2005, 06:54 PM   #34
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Quote:
Originally Posted by Pre-diddy
So all those ricers and Honda fanboy's have been right all along.



(i-)VTEC is teh fAstar!!1!one!rice!!1!
is that what they were saying? i guess to a point, yep, they were right.
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Old 01-18-2005, 06:55 PM   #35
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Newer 2.0L STi engines in Japan have AVCS for both the intake and exhaust cams. Subaru calls that configuration "Dual AVCS." The 3.0L EZ30R engine has AVCS only on the intake cams but it also has a 2-stage variable valve lift system on the intake cams as well. I think the EZ30R system is very similar in function to Honda's i-VTEC. You can see an illustration of the EZ30R's VVL system if you open up the image at:
http://forums.nasioc.com/forums/atta...chmentid=51659
The illustration on the left depicts the low load operation. Notice that one intake valve is opened more than the other - this induces more swirl/tumble. The illustration on the right depicts high load operation.
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Old 01-18-2005, 09:48 PM   #36
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and Jon comes through yet again! yeah, that's what i heard about the EZ30 engine. i surely hope that they'll come out with this engine layout for the new impreza's along with GDI.
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Old 01-18-2005, 10:07 PM   #37
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Quote:
Originally Posted by clamdip
yes, AVCS only applies to intake cam timing, not exhaust cam timing. which is why there is valve overlap.
Don't really understand that statement but anyway...

Quote:
Originally Posted by Jon [in CT]
Newer 2.0L STi engines in Japan have AVCS for both the intake and exhaust cams.
So the JDM 2.0 V8 has it just not any USDM engines...
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Old 01-19-2005, 11:36 AM   #38
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Quote:
Originally Posted by Abe Froman


So the JDM 2.0 V8 has it just not any USDM engines...
v9 i believe
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Old 01-20-2005, 08:39 PM   #39
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Quote:
Originally Posted by Soon2Bgreat
v9 i believe
ahhh...thanks...
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Old 10-01-2005, 03:46 AM   #40
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From someone who has messed with VTEC motors entirely too much, every variable valve system should be like that =x

there is no change in the cam timing as far as sprocket vs cam vs crank, the change is done by a third lobe and rocker arm as was said before.

Tiny cam for being fuel efficent, huge came for making "power"
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Old 01-31-2007, 09:13 PM   #41
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Good read. Makes me wonder about if we'll ever see Electronic Valve Control (camless engines) in the mainstream.
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Old 02-01-2007, 06:17 PM   #42
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Thanks for sharing...I had a Prelude Vtec and it was very fun to drive!! We here in Brazil also got the Civic Vti, B16A engine, from 1993-98. Tuners and ricers paradise.
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Old 02-02-2007, 12:53 AM   #43
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This information made things much more clear....good reading
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Old 02-02-2007, 01:54 AM   #44
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For the love of everything HOLY...

(yes, I'm nitpicking here)

Okay, the lift portion that people are referring to, that is available currently on the 3.0L H6 and the 2007 2.5L non-turbo engines (WRX's at least) is called AVLS, short for Active Valve Lift System.

As someone mentioned, it's only on the intake side...it helps a little bit with power, but mostly it's for emissions a la Honda and their intake-based VTEC. (e.g. intake valves open at staggered lift in low rpm/load mode, thus promoting better swirl of intake charge, etc. blah blah blah)

This comment taken from here:
Quote:
The normally aspirated Forester 2.5 X engine has an increase in horsepower from 165 to 173. The engine’s i-Active Valve Lift system contributes to that increase, varying the amount of valve lift relative to engine speed. At low rpm, intake valves are set for low and mid-lift, which swirls and accelerates the air as it goes into the engine. That improves combustion and results in higher torque (i.e., greater power). At high rpm, the system opens the valves even further, which decreases resistance to intake airflow. Again, the result is greater power. The i-Active Valve Lift system not only increases power output but improves driveability as well.
http://www.mypersonaldrive.com/Sum05...mpressions.htm

For the AVCS, which varies timing (please correct me here if I'm wrong), the layman's explanation is that being able to vary the timing will allow the engines to spread their given torque rating over a much wider range when compared to an identically spec'd engine withOUT AVCS (variable timing). Of course, this also greatly helps with emissions (reduced NOX emissions through better internal EGR effect blah blah blah).

From Subaru.com re: H6 EZ30:
3.0-liter DOHC aluminum-alloy 24-valve 6-cylinder horizontally opposed SUBARU BOXER engine with Active Valve Control System (AVCS) and Active Valve Lift System (AVLS). Iridium spark plugs.

Hope I've added something positive to this conversation...
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Old 02-02-2007, 03:32 AM   #45
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On streetfire.net there is a good video of how vtec works, just do a search under "nipo team" and it should pop up..

Last edited by STimo; 02-02-2007 at 03:52 AM.
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Old 02-05-2007, 10:43 PM   #46
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i think its funny how people forget all about the vvt-i and vvtl-i motors that toyota makes. the vvt-i is a varible valve timing intelligence motor. it has the same principles of how it works except it uses gears inside the cam gear at least the old 20v motors used that. and as for the vvtl-i thats the same but with lift. i believe instead of using a second cam profile it actually squirts oil between the lifter and some other part to give it more lift. i may be wrong. just reminding people of other types.
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Old 02-06-2007, 12:11 AM   #47
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Quote:
Originally Posted by spin'nall4 View Post
i think its funny how people forget all about the vvt-i and vvtl-i motors that toyota makes. the vvt-i is a varible valve timing intelligence motor. it has the same principles of how it works except it uses gears inside the cam gear at least the old 20v motors used that. and as for the vvtl-i thats the same but with lift. i believe instead of using a second cam profile it actually squirts oil between the lifter and some other part to give it more lift. i may be wrong. just reminding people of other types.
+1, VVTL-i > VTEC....I sorta miss my Celica...
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Old 02-06-2007, 01:09 PM   #48
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Quote:
Originally Posted by CHESTYC View Post
For the love of everything HOLY...

Okay, the lift portion that people are referring to, that is available currently on the 3.0L H6 and the 2007 2.5L non-turbo engines (WRX's at least) is called AVLS, short for Active Valve Lift System.

As someone mentioned, it's only on the intake side...it helps a little bit with power, but mostly it's for emissions a la Honda and their intake-based VTEC. (e.g. intake valves open at staggered lift in low rpm/load mode, thus promoting better swirl of intake charge, etc. blah blah blah)
Being that I have an turbocharged EZ30R H6 in my car, I can add a few comments. As mentioned above, the oil pressure based activation of the secondary cam lobe on the intake cam allows not only a change in lift but a complete change in duration and cam timing. Since the activiated follower runs on a new lobe, all three parameters can be changed. This is a simple on/off switch.

As for the effect, take a look at this graph and text from my first H6 tune.



In this graph, there are 4 pulls.

Pull 1: (red) Lift set to 3000rpm. You can see the lift kick in, and torque output drops significantly. Clearly even though there is significant boost at this point, more torque is produced with the lower lift.

Pull 2: (green) Lift set to 3500rpm. Right at 3500 rpm, you can see the dip at the lift kicks in. It seems pretty close, but perhaps just a bit early. Notice the green is the highest between 3800 and 4000.

Pull 3: (blue) Lift set to 4000rpm. You can see the torque advantage over the green from 3500 to about 3800. Above 4000, green and blue are nearly equal.

Pull 4: (purple) Lift set to 4500rpm. Again you can see the crossover at 3800, and significant torque difference above 4000.

From the above runs, the ideal turn on point appears to be around 3800 rpm, which funny enough is what my butt dyno picked on the road a few weeks ago while I was breaking the car in.


Cheers,

Jeff Sponaugle
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Old 02-09-2007, 07:24 AM   #49
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Quote:
Originally Posted by nhluhr View Post
it is advance, and the graphs show it clearly because it's not the exhaust valve that changes.
Absolutely right. My mistake. I didn't pay close enough attention to exactly what it was they were showing.

Quote:
Originally Posted by Jeff Sponaugle
Pull 1: (red) Lift set to 3000rpm. You can see the lift kick in, and torque output drops significantly. Clearly even though there is significant boost at this point, more torque is produced with the lower lift.
Though obviously what you say is 100% correct, it's probably more poignant to say, "...more torque is produced with the lower duration." That is, if the lower lift cam does indeed have shorter duration.

Presumably, what happens is that the longer duration lobe has such a late IVC that it allows too much reversion to compensate for the better initial flow until 3800 RPM. Ergo, if you had custom cams made, your low RPM lobe probably wouldn't be low lift as much as shorter duration and earlier IVC.
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Old 02-09-2007, 03:21 PM   #50
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I'd like to see some examples of AVCS tunes if there are any floating around. Theres a lot of conflicting information and my butt dyno hasn't been really conclusive when it comes to experimentation.
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