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Old 04-28-2009, 11:07 PM   #1
teslamaster
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Default Is it worth modifying the AVLS in our cars via engine management or hardware?

Is it worth modifying the AVLS in our cars via engine management or hardware?

The short answer:

NO


The long answer:

I decided to design and build a circuit to control the AVLS so that I could manually set the rpm that it switched at, and fool the ECU into thinking the system was working correctly. Due to what I learned while testing it I abandoned that idea, but I thought I would share some of the things I figured out. There are a lot of things I didn’t include here so if you have any questions feel free to ask. I may or may not be able to answer you…


Short summary of how AVLS works

Fist off, to avoid any confusion, this is AVLS not AVCS. AVLS is the “Active Valve Lift System” that is used in newer NA Subarus. AVCS is the “Active Valve Control System” used in some DOHC Subarus. AVLS actually changes the cam profile, where as AVCS changes the timing.

AVLS only modifies the intake valves. Basically there are 4 lobes on the camshaft for each cylinder. One lobe controls both exhaust valves and does not change. Another lobe controls one of the intake valves and also does not change any. The last two lobes are the heart of the AVLS. The other intake valve can be controlled by either of these two lobes. One has a higher lift longer duration and the other has a lower lift and shorter duration.

For those interested… In low lift mode the variable intake valve opens at 0deg BTDC, closes at -50deg ABDC, with 35.182-35.282mm lobe height. In high lift mode the variable intake valve opens at 14deg BTDC, closes at 62deg ABDC, with 40.315-40.415mm lobe height. The fixed intake valve opens at 0deg BTDC, closes at 58deg ABDC, with 40.075-40.175mm lobe height. **these numbers are for a MY06 2.5i

For the variable valve there is a low lift arm and a high lift arm. Only the low lift arm is connected to the intake valve. During low lift mode, the two arms operate separately on their own cam lobes and since the valve is connected to the low lift arm, it operates with low lift. During high lift mode, the two arms are locked together. Since the high lift lobe is higher, the high lift arm lifts the low lift arm off of it’s lobe and the valve operates with high lift. To lock the two arms together oil pressure pushes a pin inside a small cylinder between the arms. The oil pressure is controlled by the oil switching solenoid valve (one for each head), which is controlled by a pulse width modulated (PWM) signal from the ECU.


When it was thought to have switched (not correct), and why I decided to make an AVLS controller

From talking to people and searching online (forums and otherwise) it is fairly clear that most people think the ALVS switches to the high lift profile somewhere around 4000 rpm. This is “validated” by a jump in power/torque/load that can be seen in some dyno plots and logs.

That being the case I thought that it would be beneficial to turn on the high lift profile sooner, before 4k rpm. The actual gains would need to be measured, but there should be some benefit. I decided to build a physical controller because it might be a long time before the OS crowd has time to work on AVLS.


Testing

The oil switching solenoid valve (OSV) is controlled by a 300Hz PWM signal from the ECU. The ECU monitors AVLS status using an oil pressure switch. It was unclear whether the duty cycle of this PWM signal just switches between two values or if it was continuously changing and “switches” at some point. The relationship between the OSV signal and the output of the oil pressure switch was also unclear. These things needed to be tested as well as when it actually turns the OSV on and off.

I basically just wired a battery powered oscilloscope into the ECU harness to measure these signals and had a friend drive the car to vary rpm and throttle input. I also measured the continuity between the measuring points on the ECU harness and the actual valve and sensor just to be sure it was the right signal.


Testing results

The signal to the OSV switches abruptly between ~33% duty cycle (off) and ~80% duty cycle (on). The oil pressure switch follows the change in OSV duty cycle with very little lag. The switching point is at a MUCH lower rpm than was previously thought.

The switching point is determined by both rpm and engine load. On a WOT pull, the AVLS switches to high lift a little before 1500 rpm and stays high to redline. Below ~1500 rpm it is always low lift. Between ~1500 and ~2500 rpm with no throttle it is low lift, and with very light throttle (<15%) it switches to high lift. Above ~2500 rpm it is always high lift (with one exception**).

In the 1500-2500 rpm band the delay between throttle input and switching to high lift is negligible.

My car was tuned to have no open loop delay for the first set of tests. The tests were repeated with a stock tune and the results were the same.

** when in gear dropping from a high rpm with NO throttle it will switch to low lift at ~3000 rpm. With any throttle input it will immediately switch back to high lift.


Summary

There is no need to modify the AVLS switching points. Anywhere where the hotter cam profile would have any possibility of helping, it is turned on from the factory. There is no use in me building a controller, and no use in the OS guys finding the AVLS stuff when there are other useful things that can be worked on.
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Last edited by teslamaster; 04-28-2009 at 11:33 PM.
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Old 04-28-2009, 11:15 PM   #2
williaty
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FWIW, I was the driver working with him on this. Teslamaster knows his ****.
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Old 04-28-2009, 11:18 PM   #3
watchunglava
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wow dude !!!!!! thank you so much . thats all i can say. thank you . and possibly , you are the ****ing man dude !

btw tesla as in the band or the genius?
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Old 04-28-2009, 11:26 PM   #4
teslamaster
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Thanks for all the help Ty!

Quote:
Originally Posted by watchunglava View Post
wow dude !!!!!! thank you so much . thats all i can say. thank you . and possibly , you are the ****ing man dude !

btw tesla as in the band or the genius?
No problem!

Actually, I built a decent sized Tesla Coil back in high school and started using the screen name then.

Last edited by teslamaster; 04-29-2009 at 12:21 AM.
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Old 04-28-2009, 11:35 PM   #5
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Thanks for taking this one step further and actually going experimental, or at least thanks to getting to it before I did! Well done Sir.

I'm not entirely convinced that there can't be gains made here (total power, not peak) but my curiosity is satiated until at least one other cam grind shows up on the market.
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Old 04-28-2009, 11:59 PM   #6
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There's definitely gains to be made via the cam itself. The point is that the stock ECU switches to the high-lift lobes so quickly that there's no value in trying to get it to switch sooner.
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Old 04-29-2009, 12:01 AM   #7
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yea exactly i can see where the dude got confused though . at the end there it sounds like you can get gains higher than the stock high cam lobe but i understood what the op was saying.

the gains to be made are by getting an aftermarket cam with even higher lobes .
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Old 04-29-2009, 12:02 AM   #8
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* can't
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Old 04-29-2009, 12:19 AM   #9
teslamaster
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Yep, definitely gains to be made with an aftermarket cam. Actually, the AVLS should make aftermarket cams a little better because you can change all of the lobes except the low lift lobe. Leaving the low lift lobe unchanged would help out with idle and not affect the performance of the cams in places that it matters.
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Old 04-29-2009, 02:36 AM   #10
Jerry Xu
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Reading this was like drinking a good glass of wine. This is fantastic. Thank you man!
Looks like Subaru did its homework on this. A few guys I spoke to confirmed that the new delta cams for the 2.5i didn't have ANY idle issue only pulls strong, although I don't fully understand why 1 low profile will help the idle. If someone can share the insight.
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Old 04-29-2009, 03:57 AM   #11
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I'm rather new to variable valve systems, but my questions would be:

When the 2.5i's reach 4,000 rpms, the slight kick that a person feels is really the "immediate" increased fuel and air flow at that rpm range (since the high lifts are actually opening earlier than previous thought)?
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Old 04-29-2009, 04:01 AM   #12
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Quote:
Originally Posted by FLZ_Boy View Post
I'm rather new to variable valve systems, but my questions would be:

When the 2.5i's reach 4,000 rpms, the slight kick that a person feels is really the "immediate" increased fuel and air flow at that rpm range (since the high lifts are actually opening earlier than previous thought)?
It can be coming from a great number of things. It's possible the resonant tuning of either the intake or the exhaust peaks there. It's possible that the stock cams "come on" (meaning increase in efficiency due to their basic design) at that point. It's possible that it's doing something funky with the tune there (I've never looked with the specific intent of finding that out). There's just a lot of things that could be happening and the cam switchover is just the first thing that has been crossed off the list.
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Old 04-29-2009, 11:46 AM   #13
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im on lunch break from work. i gotta read this whence i return home. i have always wondered about that funny acronym.
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Old 04-29-2009, 11:56 AM   #14
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Does the fact that 4k rpm is peak torque have anything to do with that feel?

So AVLS is 06+, huh?
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Old 04-29-2009, 12:12 PM   #15
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this thread is too awesome for noobs . please just stop right now .

if your clueless read this first .

http://www.drive.subaru.com/spring07_whatmakes.htm


teslamaster just filled in alot of blanks! and really got me excited to throw some delta cams in my heads .

you have to realize guys , a number of people have been holding off on head work because of a foggy mist around the i avls in modern n/a subies .

now that teslamaster has figured out that the low cam lift if purely if your driving like grandma and anytime you tap the gas your going high lift , its like finding the dead sea scrolls .

its the perfect set up.

crusing in 5th on the highway at 60 with little throttle ? low profile and great on gas !

pretty much anytime you hit the gas ? high lift profile!

i love it , its so much better than v tec ! with v tec it takes forever for it to "kick in".

most people confused that kick in at 4k ish for i avls, because obviously its a kick in the pants , and well hondas vtec kicks in around there like that .

with i avls, its pretty much allways high lift , and only low lift when your trying to get like 28mpg, or idling at a stop light .

again amazing work teslamaster ! great great contribution.
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Old 04-29-2009, 12:19 PM   #16
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Quote:
Originally Posted by watchunglava View Post
this thread is too awesome for noobs . please just stop right now .

if your clueless read this first .


http://www.drive.subaru.com/spring07_whatmakes.htm
Thanks.
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Old 04-29-2009, 01:41 PM   #17
teslamaster
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Quote:
Originally Posted by chazly413 View Post
Does the fact that 4k rpm is peak torque have anything to do with that feel?

So AVLS is 06+, huh?
The increase ~4k I was referring to I observed on various dyno plots and logs. I never trust "feel". "Feel" is generally correlated to torque though, so an increase in torque at any rpm should feel better...

Yes, the AVLS is in 06+ for the most part. I think it may have been used in some of the 3.0 liter engines in 05, but I'm not 100%. Someone here would probably know...

Quote:
Originally Posted by watchunglava View Post
crusing in 5th on the highway at 60 with little throttle ? low profile and great on gas !
Actually, you are probably going to be using the high lift profile whenever you are cruising on the highway. It only takes a VERY small amount of throttle between 1500 and 2500 to switch to high lift, and anywhere above that is almost always high lift.
Quote:
Originally Posted by watchunglava View Post
pretty much anytime you hit the gas ? high lift profile!
Yes.
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Old 04-29-2009, 02:37 PM   #18
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So why would 1 of 4 profiles not ground will improve idling?
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Old 04-29-2009, 02:40 PM   #19
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Because there's not as dramatic a drop in idle vacuum, mainly.
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Old 04-29-2009, 03:26 PM   #20
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speaking of avls... anyone have or heard of their oil pressure sensors blow up? I just had one replaced under warranty.. it pissed out 3 qts of oil in 2 weeks
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Old 04-29-2009, 04:03 PM   #21
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sounds like my motor right now!!!!!!!!

would the oil pressure sensor send off a cel? because i have checked almost everything and still can't figure out why im loosing 3-4 qts a month !!!!!
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Old 04-29-2009, 04:22 PM   #22
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You should be able to see if you are loosing oil out of the AVLS oil pressure sensor. It is located right behind the OSV (do you know where that is?). There is one for each head. It is very visible.
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Old 04-29-2009, 04:28 PM   #23
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Quote:
Originally Posted by williaty View Post
There's definitely gains to be made via the cam itself. The point is that the stock ECU switches to the high-lift lobes so quickly that there's no value in trying to get it to switch sooner.
Im surprised you didnt fight op




jk <3 williaty
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Old 04-29-2009, 04:28 PM   #24
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Quote:
Originally Posted by Un0RiGiNaL View Post
Im surprised you didnt fight op
?????
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Old 04-29-2009, 04:39 PM   #25
Sir-Knight
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Quote:
Originally Posted by watchunglava View Post
sounds like my motor right now!!!!!!!!

would the oil pressure sensor send off a cel? because i have checked almost everything and still can't figure out why im loosing 3-4 qts a month !!!!!
I lost 1 1/2 qt on a 500 km drive out of the left bank sensor, but when this one leaks it's very visible since it smokes as it drains onto the headers, and it will also leak all over the top of the block under the oil filler neck.

My engine threw no code or CEL during the last 2 weeks when the leak started.

The sensor has a white cap and wire coming from it at the base of the filler neck on the left head, on the right head it's at the back of the engine, still on top but the intake piping makes it a little hard to get to, but it will look identical.

Also, it took a few days and a good 500-800 km of driving for enough oil to cover the top of the block and work it's way down onto the plastic skid plate and headers, so it took a while for a puddle of oil to be seen under the car. If you car has been losing oil for a whole month now, you should be seeing it when you park. If the right bank sensor is leaking though, it will run and drip right off the block and onto the ground, I dont' think it will hit the exhaust at all, whereas the left sensor will drain all over the exhaust headers to stink and smoke.
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