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Old 11-24-2012, 01:55 PM   #676
Jubert69
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I've done a bunch of reading in this thread, and I'm a noob. Can someone explain what overlap means?
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Old 11-24-2012, 04:40 PM   #677
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Originally Posted by Jubert69 View Post
I've done a bunch of reading in this thread, and I'm a noob. Can someone explain what overlap means?
"Overlap" refers to the period of time, near the end of the exhaust stroke and the beginning of the intake stroke, when the intake and exhaust valves are open at the same time. For the exhaust valves, this is right before they close. For the intake valves, this is right after they have opened.

It might be counter-intuitive at first, but a carefully tuned amount of overlap can yield more power than no overlap at all. The lumpy idle that muscle-cars have with big cams is a side-effect of a relatively large amount of overlap. At higher RPM it's a good thing, but at idle it behaves like your intuition would lead you to expect - the motor pulls in some exhaust during the intake stroke, and combustion suffers.

With adjustable valve timing, we can tune the overlap to occur only in the conditions where it's actually helpful, so we get the increased volumetric efficiency in the midrange, but without the lumpy idle.
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Old 11-24-2012, 04:57 PM   #678
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Hear me out on this, let me know if I need to clarify.

0 AVCS = Acts like Small Cams
20-30 AVCS = Acts like Bigger Cams

So around low loads, you want little to no overlap, which is low AVCS and higher loads want more AVCS because of overlap?
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Old 11-24-2012, 10:37 PM   #679
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Originally Posted by Jubert69 View Post
Hear me out on this, let me know if I need to clarify.

0 AVCS = Acts like Small Cams
20-30 AVCS = Acts like Bigger Cams

So around low loads, you want little to no overlap, which is low AVCS and higher loads want more AVCS because of overlap?
Not really. It does not work like that. Unfortunately, it is not that simple. The muscle car example was just an illustration of how overlap can affect an engine. In our case, it really depends on the scenario. Load is just one axis. You also have to consider RPM. Some low load situation call for fair amount of overlap to produce internal EGR effect which yields better fuel economy and lower emissions. In high load situations, you typically do not want lots of overlap because the positive pressure on the intake side will force the charge into the chamber and the engine does not rely heavily on scavenging to improve volumetric efficiency. I say typically because the exhaust side also influences this and depending on what you're running there, the overlap requirement may change. The more flow you can get on the exhaust side, the more you might be able to use overlap to improve VE.
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Old 10-24-2013, 03:42 AM   #680
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Not really. It does not work like that. Unfortunately, it is not that simple. The muscle car example was just an illustration of how overlap can affect an engine. In our case, it really depends on the scenario. Load is just one axis. You also have to consider RPM. Some low load situation call for fair amount of overlap to produce internal EGR effect which yields better fuel economy and lower emissions. In high load situations, you typically do not want lots of overlap because the positive pressure on the intake side will force the charge into the chamber and the engine does not rely heavily on scavenging to improve volumetric efficiency. I say typically because the exhaust side also influences this and depending on what you're running there, the overlap requirement may change. The more flow you can get on the exhaust side, the more you might be able to use overlap to improve VE.
Hi Ziggyrama
If you had to switch intake only avcs (because wiring wise and time mandate it) in an on/off manner (lets agree off is 0deg and on in 30?)
How would you switch it? rpm or load based? of use both axis?
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Old 10-24-2013, 04:57 AM   #681
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Hi Ziggyrama
If you had to switch intake only avcs (because wiring wise and time mandate it) in an on/off manner (lets agree off is 0deg and on in 30?)
How would you switch it? rpm or load based? of use both axis?
If I had to choose 1, I would take RPM. Just because for relatively small turbo sizes that majority of Subarus use, exhaust backpressure is high at upper RPM range, say above 5000. You dont' want overlap there.
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Old 10-24-2013, 03:32 PM   #682
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If I had to choose 1, I would take RPM. Just because for relatively small turbo sizes that majority of Subarus use, exhaust backpressure is high at upper RPM range, say above 5000. You dont' want overlap there.

so basically avcs on (advanced) from 1500 till 5000 and off (retarded) at idle and above 5000.. right?
could I have any issues with valves touching themselves with kelfords 272 both 11.3 in and 10.7ex
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Old 10-24-2013, 04:15 PM   #683
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Do not try to switch 12 volts to the solenoids. You will destroy the valves and likely the engine. The system is meant to be a closed loop system with pulsed 12 volts PWM.
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Old 10-25-2013, 12:13 AM   #684
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Do not try to switch 12 volts to the solenoids. You will destroy the valves and likely the engine. The system is meant to be a closed loop system with pulsed 12 volts PWM.
hi clark, pwm either the 12v or the earth signal should result the same as the other pin should have a constant... Right? I checked with the stock ecu 12v is constant and earth is pwm.
100%duty cycle is a constant pulse will move the cams how many degrees? 30?
So if I where to physically lock the cams 30 deg advanced I could see if they touch each other, I have no issue with piston as they are the deep carved type instead of the stock flats.
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Old 10-25-2013, 12:56 AM   #685
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I am aware of how the system works. What you are suggesting is what we all tried 10 years ago and it will burn out the solenoids and with your cams, the valves will hit. But by all means try it out.
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Old 10-25-2013, 07:49 AM   #686
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so basically avcs on (advanced) from 1500 till 5000 and off (retarded) at idle and above 5000.. right?
could I have any issues with valves touching themselves with kelfords 272 both 11.3 in and 10.7ex
That will not be optimal by any means. 30 degree advance between 1500 and 5000 RPMs will give you OK drivability around town but high load scenarios will leave power on the table. Your fuel economy will also not be so good. Not sure what you're trying to do but be aware that you're trying to make it something it wasn't meant to do.
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Old 10-25-2013, 12:26 PM   #687
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I am aware of how the system works. What you are suggesting is what we all tried 10 years ago and it will burn out the solenoids and with your cams, the valves will hit. But by all means try it out.

Whats up with the attitude?
Anyways, we decided to let the system off as the car will be mostly drag racing... About the solenoids burning... Maybe in the long run...
We'll perform the test locking the pulleys in the most advanced position and turning the engine by hand, using fiber optics see how close they get
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Old 10-25-2013, 12:29 PM   #688
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Originally Posted by Ziggyrama View Post
That will not be optimal by any means. 30 degree advance between 1500 and 5000 RPMs will give you OK drivability around town but high load scenarios will leave power on the table. Your fuel economy will also not be so good. Not sure what you're trying to do but be aware that you're trying to make it something it wasn't meant to do.
Thanks ziggygrama
So basically the advance is good for low to mid rpms at low load sites but not good on the higher load sites, which gives a good idea of how the map should look like.
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Old 10-26-2013, 12:03 PM   #689
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Whats up with the attitude?
Anyways, we decided to let the system off as the car will be mostly drag racing... About the solenoids burning... Maybe in the long run...
We'll perform the test locking the pulleys in the most advanced position and turning the engine by hand, using fiber optics see how close they get
This could be worth a look
http://forums.nasioc.com/forums/show...1475616&page=3
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Old 10-28-2013, 01:29 PM   #690
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I don't have an attitude at all. You asked and I told you what would happen. You have aftermarket cams and they will hit in my experience. Even if you did this and you had cams that would not hit, this would not be worth it. You need proper closed loop control. Sounds like you are new to all this. But this has been tried many many many times on Stand alones and the results where destroyed engines or poor performance. If the car is a drag car, rip AVCS off the car. It would never be active anyways.




Quote:
Originally Posted by jasaircraft View Post
Whats up with the attitude?
Anyways, we decided to let the system off as the car will be mostly drag racing... About the solenoids burning... Maybe in the long run...
We'll perform the test locking the pulleys in the most advanced position and turning the engine by hand, using fiber optics see how close they get
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Old 11-16-2013, 06:00 PM   #691
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Since the last build, I've had problems with my avcs working properly, My left side intake is only coming up to 4 to maybe 6* max, the passenger side comes up to 25 or so, I believe we were going for 30-35 though, during the last removal I saw the cam gear probably wasnt cared for enough while removing the bolts for timing belt removal, My best guess right now is saying its one of the upper (intake) cam gears, but at 150 a piece Id like to know for sure, motor is out right now, Ive had my new kelford cams inspected, swapped avcs solenoids with a working sti's, made sure no filter where in banjo's

Id like to know for sure what it is, I tried everything I could while it was in the car, short of changing cam sensors

Thanks in advance CAR IS AN 04 STI USDM (SINGLE AVCS)
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Old 05-03-2014, 12:30 PM   #692
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Maybe I'm resurrecting the thread here, but I had a friend with an 04 STi same issue with cam advance. It ended up being one of the screens in the banjo bolts having been sucked into the oil line and impeding flow. You may want to check that if you haven't already.
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Old 05-03-2014, 02:44 PM   #693
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filters are a known culprit
we had a car with odd avcs behavior, where one side was really late to advance untill 3000 rpm

ended up being faulty cam gear, fyi
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Old 05-03-2014, 06:41 PM   #694
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Maybe I'm resurrecting the thread here, but I had a friend with an 04 STi same issue with cam advance. It ended up being one of the screens in the banjo bolts having been sucked into the oil line and impeding flow. You may want to check that if you haven't already.
Not possible. Someone told you a story.

For one, there is no "suck" on that line, only pressure. Secondly, there is not enough flow to push that screen out of the bolt... ever look at it? Even if it gets completely blocked all it does is impede flow.

That screen is going nowhere.
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Old 05-09-2014, 06:35 AM   #695
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Not possible. Someone told you a story.

For one, there is no "suck" on that line, only pressure. Secondly, there is not enough flow to push that screen out of the bolt... ever look at it? Even if it gets completely blocked all it does is impede flow.

That screen is going nowhere.
A story? It was a friends car, but we pulled the screen out in my garage. It had deteriorated to the point where it fell apart. Part of it was in the bolt, part of it was in the solenoid.

You say that there is no suck, just pressure. By the very definition, sucking results from pressure. For example, a vacuum creates a low pressure in it's tank, which than sucks air in.

I'm just trying to help the OP here in letting them know that the little screens are known to cause AVCS issues.
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Old 11-16-2014, 05:44 PM   #696
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good thread for discussion...
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Old Today, 04:58 AM   #697
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Originally Posted by SeeeeeYa View Post
Not possible. Someone told you a story.

For one, there is no "suck" on that line, only pressure. Secondly, there is not enough flow to push that screen out of the bolt... ever look at it? Even if it gets completely blocked all it does is impede flow.

That screen is going nowhere.

Have also seen the screen filter collapse under pressure and oil pressure pushed it into the cam gear
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