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Old 01-13-2002, 02:41 PM   #1
scooby5
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Default A technical primer on Subaru AVCS Engines.

Hi There,

I've been reading posts on the board for a while mentioning the JDM AVCS engines and a lot of misinformation associated with it. So I decided to present this primer on AVCS engines. Hope you like it!

First off, the Subaru AVCS technology found in the 2001 STi isn't new. It has been around for a while and was standard equipment on the previous JDM GC8 Impreza SRX 2.0. This same technology is now found in the turbo engines and used more aggresively.

Most of the following information is from a Subaru STi technical description document I have. Here goes.

Active Valve Control System

The purpose of AVCS is the increase engine power and torque output while at the same time gaining improvements in fuel consumption, exhaust emissions and idling stability. By controlling the intake valve timing to suit the engine load and speed conditions this system optimises the engine volumetric efficiency and combustion process.

This is achieved by rotating the camshaft sprocket relative to the intake camshaft within a maximum range of 35 crankshaft degrees.

This movement is controlled by the engine management computer based on input signals from:
  • Air Flow sensor
  • Engine coolant temperature sensor
  • Throttle position sensor
  • Camshaft position sensor

The ECM then generates a duty ratio electrical output signal to an Oil Control Valve (OCV) positioned at each intake camshaft sprocket to control engine oil pressure which is supplied to advance and retard chambers within the avcs actuator.

Valve timing is continuously and infinitely variable within the 35 crank degree range and controlled according to engine speed and load conditions. There are three computer maps that are used depending on the conditions to provide maximum valve timing for stable idling, improved fuel consumption in the medium speed range and maximum power at high engine speed and load.
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Old 01-13-2002, 03:29 PM   #2
illmatic
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Good info.
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Old 01-13-2002, 03:47 PM   #3
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Wonder how difficult it will be to fit this system on an earlier model. Also, I wonder how much extra power is gained from this. Would be interesting to see a non AVCS and AVCS dyno chart overlaid.

-Michael
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Old 01-13-2002, 05:54 PM   #4
Godmal
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Looks VERY similar to BMW's VANOS technology. This is used more to increase usable power throughout the power band more than peak power. Oh yeah, you get fuel economy and emissions benefits, too.
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Old 01-13-2002, 07:38 PM   #5
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With one exception, the absence of exhaust valve control. Thats too bad...



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Old 01-13-2002, 07:48 PM   #6
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Suicidal, Why would you WANT to run both cams? Regardless of what STI claims this is ONLY for emissions. Why I say that is that they could get the SAME or MORE power with out running it. However it would have lower MPG, higher emissions, and idle like 3cyl with bad rings. See what they do is put in a nice lumpy cam in with a fair ammount of overlap in the "normal" condtion. Then for idle and low speed use (places where MPG and emmisions count the most) they use that to pull almost all of the overlap out. Then in the mid range they give it the overlap back, and maybe add some more into the high end.
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Old 01-13-2002, 09:56 PM   #7
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Varying the overlap isn't nearly as big of a deal as being able to vary the valve lift. I agree, this is clearly more for emissions and a smoother idle than anything else. The scavenging effect just isn't as much of an issue at certain rpms as it is at others, so it's logical to want to be able to do this. It's not something that makes me want to hunt down an STI engine, however.

What's wrong with the idle of a big, lumpy cam?

Cmon, you know you want that bahbuhbuhbahbuuhbahah *violent shaking* idle!
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Old 01-14-2002, 12:54 AM   #8
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Default dumb question?

Could a unichip plug into a ecu wire to manipulate this system to somehow gain power from the engine?

Does this system adversely effect performance with unichips and other systems that maipulate the computer?
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Old 01-14-2002, 01:17 AM   #9
XT6Wagon
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Conduit, I agree that big lumpy cams are fun. Plus you can always let the car idle at 1,000 rpm to smooth it out a bit. Thanks to honda, people somehow never have figured out that NONE of the current varible timing methods are about performance. They are all about reducing emissions and increasing MPG. Of course in more than a few cases they have prevented performance cars from becomming a modern clone of the 140 HP Corvette.
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Old 01-14-2002, 11:44 AM   #10
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good info...

i was also under the impressing that the JDM 2.5 also had this

but he info that it is infinatly viarable in cool

i would think that tuing to that would be difficult ..
to use it to its full potential you would need a 4th demintion in the fuel map (1-2-3 being TPS-injector-timing)
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Old 01-14-2002, 01:36 PM   #11
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Jaxx,

As far as I know there is no 2.5 Impreza in JDM! The Forester T/25 2.5L is a DOHC, and does have AVCS (167HP), so does JDM 2.0 NA Impreza Sportswagon also has the AVCS.

Being designed around the intake camshaft, it wouldn't be available on SOHC engines as the current design stands.

So the JDM Impreza I's 1.5 SOHC doesn't have AVCS.

Last edited by scooby5; 01-14-2002 at 01:47 PM.
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Old 01-14-2002, 03:15 PM   #12
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yes u are correct no jdm 2.5 IMPREZA but other models yes
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Old 01-22-2002, 10:23 PM   #13
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Definitely with ya' Conduit, coming from a 69 GTO Judge and a hybrid 69 firebird I have long since developed an affinity for a big roller cam rumble, however, though I wouldn't hunt one down, I see more benefit in valve control than simply emission control. In lieu of a crank independent implementation ( electric solenoid actuators or some such ), it accurse to me controlling the intake and exhaust allows for better/finner control, i.e. manipulating lobe separation by controlling the centerline of both the intake and exhaust lobe centerlines with less retardation/advance. Because the amount of lift you have and the speed at which the valve moves dictates the torque your engine will produce, I see no detriment to being able to chase profiles, whether intake and exhaust or intake alone . Duration is pinnacle to what the engines basic RPM range will be. Short cams produce power in the lower RPM range, and larger duration cams pull at higher RPM, usually you sacrifice bottom end power to gain top end power as you extend the duration. Supposedly, for each ten degree change in the duration at .050”, the power band moves up or down in RPM range by approximately 500 RPM’s. This being the case ( my numbers with a grain of ~salt ), it seems a Motec and vvt is a great way to tune, particularly if your environment profile changes often; this isn't even getting into how much more beneficial this should be on a car with the high variable cylinder pressure of a turbo engine, as you could basically manipulate profiles to accommodate cranking pressure, or future displacement changes. Bear in mind that my experience has all been in the large displacement old school, but the fundamentals should be the same. On an aside, has any one here put the Motec to vvt? I wonder how hard this would be to implement...



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Old 01-23-2002, 06:33 AM   #14
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I would be curious to see a diagram of how they actually feed the advance and retard chambers... it would be interesting to see how they reliably feed oil to the two seperate chambers in the rotating sprocket assembly from the static engine mounted oil control valve unit. Unless I have read the diagram completely wrong.
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Old 01-23-2002, 11:42 PM   #15
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VVT on the intake cam does more than emissions. I am not familiar with the Subaru implementation of vvt. The system used on Lexus has a few benefits other than emissions i.e weight reduction( no need for typical egr components when you can control overlap) lots of torque down low and a fairly flat torque curve. I forget the actual specs but i think the vvt allowed the redesigned V8 (in the LS400) to achieve more than half available torque at 1400 rpm and hold it fairly flat. What is the point just that vvt is not only for emissions. Now vvt with lift control is even better

my .02

Shawn
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Old 01-24-2002, 01:19 AM   #16
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Default I'm with Worry...

The oil routing isn't very clear.
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Old 04-20-2002, 11:14 PM   #17
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Does anyone know if the TEC II or similar stand alone can control the variable valves ???? thanks !
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Old 04-20-2002, 11:18 PM   #18
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It only makes me wonder why subaru didn't put this on all WRX engines, not just the STI.

This method of controlling the emissions seems far more efficient than those silly tumbler valves.
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Old 04-21-2002, 12:05 AM   #19
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It has the TVG also - !!!
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Old 04-21-2002, 05:01 AM   #20
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Al, Are you getting your TGV's removed? Did you read the thread that had a picture of blank TGV spacers for an STI RA? It seems like some do and some don't.

So I think that some regular (JDM) WRXes get AVCS and TGVs while some STIs (RAs) get AVCS without TGVs. Subaru is nuckin' futz.
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Old 04-21-2002, 10:46 AM   #21
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Quote:
Originally posted by aspera
Al, Are you getting your TGV's removed? Did you read the thread that had a picture of blank TGV spacers for an STI RA? It seems like some do and some don't.

So I think that some regular (JDM) WRXes get AVCS and TGVs while some STIs (RAs) get AVCS without TGVs. Subaru is nuckin' futz.
I dont have the engine yet sop i dont know what it has in there - - the STI wiring dirgram that I have says TVG is there in the same spot on the factory sti ecu as it is in the WRX ecu

I'll have it in about 10 days and I'll let you know!
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Old 02-13-2005, 04:58 AM   #22
cold3fuzion
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Question Avcs On My 02 Wrx!!!

Has anyone figured out if AVCS is available on my '02 WRX??????????? Wouldn't it just be a drivetrain upgrade?? With a Cam Gear that has sensors, or somewhat? [email protected]... lemme know!
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Old 02-13-2005, 09:27 AM   #23
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Scooby5
There is a JDM EJ25 with a cable throttle body belonging to the Forester STi. As it sits right rated at like 265hp it is no chump and would make short work of a USDM WRX!!! It is such a nice design Jun has slapped it into a STi and making it RWD for hopefully this upcomming D1 season!!!
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Old 02-13-2005, 02:40 PM   #24
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Quote:
Originally Posted by cold3fuzion
Has anyone figured out if AVCS is available on my '02 WRX??????????? Wouldn't it just be a drivetrain upgrade?? With a Cam Gear that has sensors, or somewhat? [email protected]... lemme know!

Wow..old thread bump from 2002 but to answer this question. No..AVCS is not available on a 02wrx. You will need to source AVCS heads and have a matching ECU to control the AVCS function.
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Old 03-28-2005, 05:40 PM   #25
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Any one know the AVCS cams specs on those models?

Hey, I have the SRX
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