A few of AVCS questions

spoolinsuby · 05-18-2005, 08:25 AM

I'm thinking about getting Ver. 8 Spec C heads and need some questions answered. I have more knowledge about Hondas than Subies, so forgive my usage of the term VTEC

1. Is AVCS the same as VTEC? (VTEC has a high lift cam lobe that the ECU switches to at a given RPM, not like variable timing but variable lift)

2. Does the ECU change the fuel map when AVCS kicks on?

3. Would it be worth it to get bigger cams or keep AVCS?

* Registered users of the site do not see these ads.

DuoMaxwell · 05-18-2005, 08:40 AM

Quote:

Originally Posted by spoolinsuby

I'm thinking about getting Ver. 8 Spec C heads and need some questions answered. I have more knowledge about Hondas than Subies, so forgive my usage of the term VTEC

1. Is AVCS the same as VTEC? (VTEC has a high lift cam lobe that the ECU switches to at a given RPM, not like variable timing but variable lift)

2. Does the ECU change the fuel map when AVCS kicks on?

3. Would it be worth it to get bigger cams or keep AVCS?

IN order

1. No its more like an advance in the timing.
2. Not to my knowledge
3. AVCS great down low but if you upgrade enough to need bigger cams your not gonna miss it!

shinsain · 05-18-2005, 08:50 AM

Hmm, I guess its good to disspell rumors...I thought AVCS was like VTEC all this time as well. I thought it was variable lift as opposed to variable timing. Hell, the WRX has variable timing.....

So what is the difference between the WRX's ability to vary timing via the ECU and the STI's "AVCS"?

DuoMaxwell · 05-18-2005, 08:54 AM

I would need the diagram to show you exactly what AVCS does. Its not the standard ECU style advance and retard in timing for det issues and the likes. The cam gears themselves adjust there is no extra larger lobe on the cams.

shinsain · 05-18-2005, 08:56 AM

Oh, so it adjusts cam timing, and not ignition timing?

DuoMaxwell · 05-18-2005, 08:59 AM

Yes I believe so. I am not that good at the new fancy JDM engines. I like the old school ones but I try to keep up with whats going on with the newer ones. If you search I think unabomber has a faq that covers AVCS.

spoolinsuby · 05-18-2005, 11:17 AM

Unabomber doeasnt have a FAQ in his manifesto post. I didnt know the WRX had variable valve timing

UkNuck · 05-18-2005, 11:44 AM

This thread may clear up a few misconceptions...

spoolinsuby, you realize AVCS won't just work w/o the matching ECU (or some suitable aftermarket control)? If you're serious about this, I suggest some searching in the Subaru Conversions forum.

spoolinsuby · 05-18-2005, 11:51 AM

Well, I was thinking if it worked off of a solenoid like VTEC does, I could turn on the AVCS with my AEM and adjust the fuel map for the AVCS when it turns on

UkNuck · 05-18-2005, 12:14 PM

The point is, it isn't an "on/off" thing. You are not just switching between 2 cam profiles (which is iirc what the VTEC does) - it's a continuous adjustment of cam angle based on SEVERAL sensor values.

zaxrex · 05-18-2005, 12:30 PM

A more expanded and annotated version of that description can be downloaded by the grace of Jon-in-CT here

spoolinsuby · 05-18-2005, 09:35 PM

ok thats what I was looking for, thanks for the responces guys

I guess when I get the heads I'll just get a set of cams and valvetrain

ebeck · 05-19-2005, 01:04 AM

The Ver 8 heads are far better than most people think. You can make power till 8500 rpm depending on turbo and tune. I would run the JDM ECU and leave them stock. You'd be shocked what power they can produce on pump prooperly tuned. And it helps a ton down low. Especially with smaller turbos like VF series.

Good luck either way!

McBain_TP · 05-19-2005, 01:26 AM

http://www.drivesubaru.com/Win05_WhatsInside.htm
A balance between increasing engine performance, improving fuel economy, reducing emissions and stabilizing idle is difficult to achieve. In its 3.0-liter 6-cylinder and turbocharged 2.5-liter 4-cylinder engines, Subaru strikes that balance using the Active Valve Control System (AVCS).

What AVCS Does and Its Effects

Pulling the connecting rod, the crankshaft pulls the piston toward the center of the engine, drawing in air and fuel from the intake system. The air and fuel enters the cylinder through the intake ports opened by the intake valves. This is like a person taking a breath – inhaling. AVCS adjusts exactly when intake valves begin to open.

With both valves closed, the turning crankshaft forces up the piston, compressing the air/fuel mixture.

The spark plug ignites this compressed mixture, causing an explosion that forces down the piston and connecting rod, which, in turn, rotates the crankshaft. These explosions within the cylinders provide the engine’s power.

The crankshaft forces the piston to the top of the cylinder again, this time pushing leftover gases out of the combustion chamber past the opened exhaust valves and into the exhaust system. This is similar to a person exhaling.

The camshaft is a very precise engine component, with lobes that open and close the intake and exhaust valves with the critical timing required for the 4-stroke cycle. AVCS changes the timing of the intake valves by adjusting the positions of the camshafts based on inputs from various sensors in the powertrain. The system varies when the camshaft lobes open and close the intake valves during the 4-stroke cycle.

The effects of variable valve control include greater power through a wider range of engine speeds, improved fuel economy and reduced emissions. But to better understand how it works, let’s start with engine basics – the 4-stroke engine cycle. ...

It goes on and on, explaining AVCS thoroughly.

spoolinsuby · 05-19-2005, 12:01 PM

Quote:

Originally Posted by ebeck

The Ver 8 heads are far better than most people think. You can make power till 8500 rpm depending on turbo and tune. I would run the JDM ECU and leave them stock. You'd be shocked what power they can produce on pump prooperly tuned. And it helps a ton down low. Especially with smaller turbos like VF series.

Good luck either way!

I was thinking about putting a set of JUN 264 cams in the V8 heads so I could pull max power from the heads since the AEM doesn't have a provision for AVCS. I'm goin to be running either a Green or a Red, I have the Green now but I may send it back for a Red.

Quote:

Originally Posted by McBain_TP

http://www.drivesubaru.com/Win05_WhatsInside.htm
A balance between increasing engine performance, improving fuel economy, reducing emissions and stabilizing idle is difficult......

Thanks for all that info, I'm goin to be here a while reading up on all the stuff that's been posted and stuff I've found

spoolinsuby · 05-19-2005, 12:04 PM

Will I see poor performance in the top end if I dont run the AVCS or will it suffer more in the low end?

spoolinsuby · 05-22-2005, 11:34 AM

anyone???

wcbjr · 05-22-2005, 11:38 AM

There are cams out now that support AVCS. AVCS is now a good thing at all RPMs.

cronic · 05-22-2005, 11:40 AM

Quote:

Originally Posted by spoolinsuby

Will I see poor performance in the top end if I dont run the AVCS or will it suffer more in the low end?

AVCS is inactive after 5500.. It ramps up then tapers down and is off by 5500.. Low end will suffer a bit with no avcs, the cams wont help low end either.. Why not be a pioneer and get a set of DPR cams which keep avcs?

bofh · 05-22-2005, 02:25 PM

OK, here is the scoop in bar english. (Words you can pronounce after a few beers) It will have several steps...

First, air has mass and inertia. It takes a while to get going and to stop. Just accept this, as it is important later...

As an engine spins faster, the air has to stop and start quicker. Now you see where step one was coming from.

A cam for high end power has to open the valves earlier, and close them later. The earlier to get started quicker, and the later because all that fast moving air can over fill the cylinder if you let it. This is a long duration cam.

Long duration cams suck at low speed. The late closing causes reversion of the intake, and you get the loping idle, and drink gas like a frat boy on a keg.

AVCS uses a moderate duration cam, but adjusts the timing so it stays open longer at high rpm, and closes earlier at low rpm. Good overfill and no reversion to worry about.

Yes, when you get real in depth this is not exactly correct, but it takes many pages to be precise. This is close enough for government work...

spoolinsuby · 05-23-2005, 01:00 AM

Wcbjr, are there any other cams besides DPR that support AVCS?

Cronic, I've never heard of DPR. Are they any good?

Thanks for that bit of tech bofh. I knew that duration is what caused lumpy idle but I didnt know what exactly why and now I do

I dont think I'll be able to use the AVCS cuz AEM doesnt have a provision for it. I'm going to try to get the AEM to work but its not lookng good

ebeck · 05-24-2005, 12:07 AM

Ditch teh AEM. Get JDM heads and ECU. Use U-tec or ECU-Tek. Both support AVCS.

Kingpin · 05-24-2005, 01:07 AM

If you do you AVCS then I suggest you use the stock ECU for that motor. On JDM ECUs the intake cam advance rolls back to 0 degrees around 6200 rpm. It depends on the map. Some run up to 40 degrees of advance down low and some only 20 degrees like the USDM STI. If you run a large turbo you can benifit from a remap of the AVCS system. My new map for the stock 05 STI remaps the AVCS and adds another 20-30 ft lbs of trq down low up to around 4k rpm. Even with no additional boost. Ignition timing GREATLY effects power output as AVCS cam angles are changes. Its an odd thing that took me 6 months to get a handle on.

Fuel maps are not changed when AVCS kicks on. In fact, on later model cars AVCS is active at Cruise.

If you go to Aftermarket non AVCS cams you will loose power below 4000 rpm. Even With HKS or JUN cams. Higher lift and more duration simply cannot match the advance of those intake cams.

If you want to keep AVCS but run a hotter cam then you have a few choices. We sell the hottest STI AVCS cam which is the V limited cam. We also sell DPR's AVCS compatible cams. If you have a USDM STI you choice is simple. Stock or DPR.

Clark

kettsupp · 05-24-2005, 04:19 AM

bookmark

spoolinsuby · 05-24-2005, 08:23 AM

My main problem is the lack of good EcuTek tuners in my area. I have EcuTek now but the only place local that does it is Mastro Subaru in Tampa, FL. They tuned my current setup and its got some drivability issues. My only other option is Subaru of Gwinnett in Atlanta, GA and that is 1400 miles roundtrip and I dont want to have to drive there if I need a reflash or have any problems. There are 2 AEM tuners within a hour from me.

05-18-2005, 08:25 AM	#1
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	A few of AVCS questions I'm thinking about getting Ver. 8 Spec C heads and need some questions answered. I have more knowledge about Hondas than Subies, so forgive my usage of the term VTEC 1. Is AVCS the same as VTEC? (VTEC has a high lift cam lobe that the ECU switches to at a given RPM, not like variable timing but variable lift) 2. Does the ECU change the fuel map when AVCS kicks on? 3. Would it be worth it to get bigger cams or keep AVCS? * Registered users of the site do not see these ads.

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05-18-2005, 08:50 AM	#3
shinsain Scooby Specialist Member#: 51745 Join Date: Jan 2004 Chapter/Region: NWIC Location: Wenatchee...WA Vehicle: LIKE A BOSS	Hmm, I guess its good to disspell rumors...I thought AVCS was like VTEC all this time as well. I thought it was variable lift as opposed to variable timing. Hell, the WRX has variable timing..... So what is the difference between the WRX's ability to vary timing via the ECU and the STI's "AVCS"?

05-18-2005, 08:54 AM	#4
DuoMaxwell Scooby Specialist Member#: 24565 Join Date: Sep 2002 Location: Misawa Japan Vehicle: 2000 V6 STi RA #856 Blue	I would need the diagram to show you exactly what AVCS does. Its not the standard ECU style advance and retard in timing for det issues and the likes. The cam gears themselves adjust there is no extra larger lobe on the cams.

05-18-2005, 08:56 AM	#5
shinsain Scooby Specialist Member#: 51745 Join Date: Jan 2004 Chapter/Region: NWIC Location: Wenatchee...WA Vehicle: LIKE A BOSS	Oh, so it adjusts cam timing, and not ignition timing?

05-18-2005, 08:59 AM	#6
DuoMaxwell Scooby Specialist Member#: 24565 Join Date: Sep 2002 Location: Misawa Japan Vehicle: 2000 V6 STi RA #856 Blue	Yes I believe so. I am not that good at the new fancy JDM engines. I like the old school ones but I try to keep up with whats going on with the newer ones. If you search I think unabomber has a faq that covers AVCS.

05-18-2005, 11:17 AM	#7
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	Unabomber doeasnt have a FAQ in his manifesto post. I didnt know the WRX had variable valve timing

05-18-2005, 11:44 AM	#8
UkNuck Scooby Guru Member#: 21808 Join Date: Jul 2002 Chapter/Region: E. Canada Location: National Capital Region Vehicle: 02 GroceryGettAr Nonemore Black	This thread may clear up a few misconceptions... spoolinsuby, you realize AVCS won't just work w/o the matching ECU (or some suitable aftermarket control)? If you're serious about this, I suggest some searching in the Subaru Conversions forum.

05-18-2005, 11:51 AM	#9
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	Well, I was thinking if it worked off of a solenoid like VTEC does, I could turn on the AVCS with my AEM and adjust the fuel map for the AVCS when it turns on

05-18-2005, 12:14 PM	#10
UkNuck Scooby Guru Member#: 21808 Join Date: Jul 2002 Chapter/Region: E. Canada Location: National Capital Region Vehicle: 02 GroceryGettAr Nonemore Black	The point is, it isn't an "on/off" thing. You are not just switching between 2 cam profiles (which is iirc what the VTEC does) - it's a continuous adjustment of cam angle based on SEVERAL sensor values.

05-18-2005, 12:30 PM	#11
zaxrex Scooby Specialist Member#: 9898 Join Date: Sep 2001 Chapter/Region: MAIC Location: VA near MD Vehicle: 2002 WRX Water Injected Blue	A more expanded and annotated version of that description can be downloaded by the grace of Jon-in-CT here

05-18-2005, 09:35 PM	#12
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	ok thats what I was looking for, thanks for the responces guys I guess when I get the heads I'll just get a set of cams and valvetrain

05-19-2005, 01:04 AM	#13
ebeck Scooby Specialist Member#: 35585 Join Date: Apr 2003 Location: Scottsdale AZ. Vehicle: RIP I'll always be The Ver8 Magistrate	The Ver 8 heads are far better than most people think. You can make power till 8500 rpm depending on turbo and tune. I would run the JDM ECU and leave them stock. You'd be shocked what power they can produce on pump prooperly tuned. And it helps a ton down low. Especially with smaller turbos like VF series. Good luck either way!

05-19-2005, 01:26 AM	#14
McBain_TP Scooby Specialist Member#: 43986 Join Date: Sep 2003 Chapter/Region: NESIC Location: Arlington, MA Vehicle: 2002 WRX wagon RIP 2003 330ci black/tan	http://www.drivesubaru.com/Win05_WhatsInside.htm A balance between increasing engine performance, improving fuel economy, reducing emissions and stabilizing idle is difficult to achieve. In its 3.0-liter 6-cylinder and turbocharged 2.5-liter 4-cylinder engines, Subaru strikes that balance using the Active Valve Control System (AVCS). What AVCS Does and Its Effects Pulling the connecting rod, the crankshaft pulls the piston toward the center of the engine, drawing in air and fuel from the intake system. The air and fuel enters the cylinder through the intake ports opened by the intake valves. This is like a person taking a breath – inhaling. AVCS adjusts exactly when intake valves begin to open. With both valves closed, the turning crankshaft forces up the piston, compressing the air/fuel mixture. The spark plug ignites this compressed mixture, causing an explosion that forces down the piston and connecting rod, which, in turn, rotates the crankshaft. These explosions within the cylinders provide the engine’s power. The crankshaft forces the piston to the top of the cylinder again, this time pushing leftover gases out of the combustion chamber past the opened exhaust valves and into the exhaust system. This is similar to a person exhaling. The camshaft is a very precise engine component, with lobes that open and close the intake and exhaust valves with the critical timing required for the 4-stroke cycle. AVCS changes the timing of the intake valves by adjusting the positions of the camshafts based on inputs from various sensors in the powertrain. The system varies when the camshaft lobes open and close the intake valves during the 4-stroke cycle. The effects of variable valve control include greater power through a wider range of engine speeds, improved fuel economy and reduced emissions. But to better understand how it works, let’s start with engine basics – the 4-stroke engine cycle. ... It goes on and on, explaining AVCS thoroughly.

05-19-2005, 12:04 PM	#16
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	Will I see poor performance in the top end if I dont run the AVCS or will it suffer more in the low end?

05-22-2005, 11:34 AM	#17
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	anyone???

05-22-2005, 11:38 AM	#18
wcbjr Scooby Guru Member#: 4001 Join Date: Feb 2001 Location: I love spherical bearings! Vehicle: 2006 Legacy GT Obsidian black	There are cams out now that support AVCS. AVCS is now a good thing at all RPMs.

05-22-2005, 02:25 PM	#20
bofh Scooby Specialist Member#: 59287 Join Date: Apr 2004 Chapter/Region: TXIC Location: Houston, Tx Vehicle: 2007 WRB WRX 2004 WRB WRX (RIP)	OK, here is the scoop in bar english. (Words you can pronounce after a few beers) It will have several steps... First, air has mass and inertia. It takes a while to get going and to stop. Just accept this, as it is important later... As an engine spins faster, the air has to stop and start quicker. Now you see where step one was coming from. A cam for high end power has to open the valves earlier, and close them later. The earlier to get started quicker, and the later because all that fast moving air can over fill the cylinder if you let it. This is a long duration cam. Long duration cams suck at low speed. The late closing causes reversion of the intake, and you get the loping idle, and drink gas like a frat boy on a keg. AVCS uses a moderate duration cam, but adjusts the timing so it stays open longer at high rpm, and closes earlier at low rpm. Good overfill and no reversion to worry about. Yes, when you get real in depth this is not exactly correct, but it takes many pages to be precise. This is close enough for government work...

05-23-2005, 01:00 AM	#21
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	Wcbjr, are there any other cams besides DPR that support AVCS? Cronic, I've never heard of DPR. Are they any good? Thanks for that bit of tech bofh. I knew that duration is what caused lumpy idle but I didnt know what exactly why and now I do I dont think I'll be able to use the AVCS cuz AEM doesnt have a provision for it. I'm going to try to get the AEM to work but its not lookng good

05-24-2005, 12:07 AM	#22
ebeck Scooby Specialist Member#: 35585 Join Date: Apr 2003 Location: Scottsdale AZ. Vehicle: RIP I'll always be The Ver8 Magistrate	Ditch teh AEM. Get JDM heads and ECU. Use U-tec or ECU-Tek. Both support AVCS.

05-24-2005, 01:07 AM	#23
Kingpin Vendor Member#: 41252 Join Date: Aug 2003 Chapter/Region: SWIC Location: 602-795-3036 Vehicle: Twin 2005 600WHP FormulaD/TimeAttack Sti's	If you do you AVCS then I suggest you use the stock ECU for that motor. On JDM ECUs the intake cam advance rolls back to 0 degrees around 6200 rpm. It depends on the map. Some run up to 40 degrees of advance down low and some only 20 degrees like the USDM STI. If you run a large turbo you can benifit from a remap of the AVCS system. My new map for the stock 05 STI remaps the AVCS and adds another 20-30 ft lbs of trq down low up to around 4k rpm. Even with no additional boost. Ignition timing GREATLY effects power output as AVCS cam angles are changes. Its an odd thing that took me 6 months to get a handle on. Fuel maps are not changed when AVCS kicks on. In fact, on later model cars AVCS is active at Cruise. If you go to Aftermarket non AVCS cams you will loose power below 4000 rpm. Even With HKS or JUN cams. Higher lift and more duration simply cannot match the advance of those intake cams. If you want to keep AVCS but run a hotter cam then you have a few choices. We sell the hottest STI AVCS cam which is the V limited cam. We also sell DPR's AVCS compatible cams. If you have a USDM STI you choice is simple. Stock or DPR. Clark

05-24-2005, 04:19 AM	#24
kettsupp Scooby Specialist Member#: 68891 Join Date: Aug 2004 Location: socal carson	bookmark

05-24-2005, 08:23 AM	#25
spoolinsuby Scooby Specialist Member#: 80182 Join Date: Jan 2005 Location: Spring Hill, FL Vehicle: 2007 Civic Si Sedan Habanero Red Pearl	My main problem is the lack of good EcuTek tuners in my area. I have EcuTek now but the only place local that does it is Mastro Subaru in Tampa, FL. They tuned my current setup and its got some drivability issues. My only other option is Subaru of Gwinnett in Atlanta, GA and that is 1400 miles roundtrip and I dont want to have to drive there if I need a reflash or have any problems. There are 2 AEM tuners within a hour from me.