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Old 09-21-2006, 01:25 PM   #126
root
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Quote:
Originally Posted by WolfPlayer View Post
Boost is created via a spinning turbine. The faster you spin the turbine, the more boost you create.
I'm not sure I'd say that, exactly. I would agree that the faster you spin the turbine, the more air you flow through the turbo (ignoring compressor efficiency issues). More air doesn't always mean more boost. Without a restriction, more air will not yield more boost.
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Old 09-21-2006, 01:32 PM   #127
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Sometimes, it helps me to think about things in a "supercharger frame of mind".

e.g. ...if the compressor speed is fixed or matched to RPM, then it's easier to see how things are really working.

Let's say that you install a high-flowing exhaust manifold on a supercharged car. Prior to the install, your boost gauge would show 10psi, all day, every day. After the install, it only shows 8psi... By uncorking the exhaust, you made the system more efficient, so some of the air/boost that was getting "backed up" in the intake manifold is now getting into the motor.

On a turbocharged car, the first thing we'd do (or our boost controller would do for us) would be to turn the boost back up... right to 10psi. So we'd (hopefully) see even *more* gains.
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Old 09-21-2006, 02:36 PM   #128
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Quote:
Originally Posted by WolfPlayer View Post
Ok. I'll admit to thinking that this is a little more complicated than that.

Boost is not the air that the ingine is not ingesting. Boost is fresh air. Period. Boost is created via a spinning turbine. The faster you spin the turbine, the more boost you create. Simple as that (yes, I know that you are aware of all of this ). So, we need to answer the question as to why advancing the intake cam allows for the turbine to be spun faster and how THAT relates to the VE of the motor.

More airflow in the preturbo exhaust means a faster spinning turbine (assuming static WGDC). More exhaust airflow CAN be due to consuming more air/fuel during combustion do to trapping more of the intake charge (and the exhaust helping to pull in the new charge a tad bit). That would mean a higher VE since we are trapping more air/fuel during the combustion stroke.

So, in relation to a faster spinning turbine, how are you determining that you have LESS VE?.

t
Take a turbo spin it at X rpm.
At X rpm into a closed container the turbo will make 10psi.
At X rpm with no container the turbo will make 0psi.

Example 1 has a lowwer VE. The flow is restricted so you get boost.
Example 2 has a very high VE. The flow is unrestricted so you get 0 boost.

So boost is a measure of the restriction to flow. If you flow more air through the motor the turbo will make less boost at the same shaft speed.
Does this mean less power? No you will probablly make more power at less boost because the air flow is higher.

TMS
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Old 09-21-2006, 03:16 PM   #129
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I love backwards thinking. I don't mean backwards as in wrong. I mean backwards in terms of thinking in a different manner to end up with the correct result.

I was thinking of boost in terms of the turbine. But, yes, of course, boost is also a measure of restriction. For example, a set of ported heads on a V8 supercharged camaro will lower the boost. But, the car will be making the same power. There is less of a restriction so you can get the same amount of air into the car with less boost (pressure).

3 of us now have reported that increasing AVCS in the upper RPMs increased the boost. The increase in overlap could put the motor in a state where the exhaust back pressure is working against the intake charge and thus creating more boost pressure because there is more of a restriction (the restriction being the exhaust pressure that it has to push against).

So far, this has been the most productive AVCS conversation I have seen on the net in the scooby community.

t
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Old 09-21-2006, 03:36 PM   #130
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Quote:
Originally Posted by WolfPlayer View Post
I love backwards thinking. I don't mean backwards as in wrong. I mean backwards in terms of thinking in a different manner to end up with the correct result.
Everyone tells me I don't think right.

Quote:
Originally Posted by WolfPlayer View Post
I was thinking of boost in terms of the turbine. But, yes, of course, boost is also a measure of restriction. For example, a set of ported heads on a V8 supercharged camaro will lower the boost. But, the car will be making the same power. There is less of a restriction so you can get the same amount of air into the car with less boost (pressure).
Sometimes thinking of a totally different system can help. Wierd huh.


Quote:
Originally Posted by WolfPlayer View Post
3 of us now have reported that increasing AVCS in the upper RPMs increased the boost. The increase in overlap could put the motor in a state where the exhaust back pressure is working against the intake charge and thus creating more boost pressure because there is more of a restriction (the restriction being the exhaust pressure that it has to push against).
That is why I have been itching for a MHI 8cm bolt on housing. I have a spare UP/DP. If I have to reflange to get an 8cm then F it I should just flang it for a 10cm.
Most of the research you do on cam overlap is for NA apps. With the small exhaust housing that are bolt on, the EGBP can reach higher than 2X intake manifold pressure. When that happens IMO the increase in overlap with higher AVCS advance, increases reversion. Wich might cause an increase in intake manifold pressure.

Quote:
Originally Posted by WolfPlayer View Post
So far, this has been the most productive AVCS conversation I have seen on the net in the scooby community.
Nevaaar not on NASIOC.


TMS
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Old 09-21-2006, 04:19 PM   #131
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Quote:
Originally Posted by ride5000 View Post
if the boost goes up, your wgdc hasn't changed, and the turbo isn't creeping, then your VE has dropped.

there isn't a doubt in my mind that this is true.
And in over simplified terms, I'd agree with that 100%.

Jorge (RiftsWRX)
www.ProjectWRX.com
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Old 09-21-2006, 10:49 PM   #132
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Ok. Tonight I test drive the JDM WRX. It felt good.

I flashed in the new AVCS map and the car was very responsive, even hitting the redline faster than ever. The car revs so easy now.

A measure of power was that the car was semi difficult to keep straight.

The car came semi slippery (tires may need some air), but after the reflash, it was bad.

The changes was not to aggressive, but the note of the car slightly changes.

The distinct WRX sounds was moving into a EL header sound.

I will have to do more logging, but I will keep everyone updated on this issue.
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Old 09-22-2006, 08:21 AM   #133
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Quote:
Originally Posted by TheMadScientist View Post
With the small exhaust housing that are bolt on, the EGBP can reach higher than 2X intake manifold pressure.
even worse--i think for most of the commonly used turbos on these motors it's more like 3x.

so i completely agree that if the overlap is too great it's literally going to push the intake charge right back out.
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Old 09-22-2006, 09:24 AM   #134
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Funny-

I was just talking to Mark the other day about installing a pressure gauge in my header to measure EGBP....Now, I'm really tempted to do it. I'd also like to get my hands on an 8cm housing for my td05 16g so I can do a before and after test.....

So much fun, so little time.....
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Old 09-22-2006, 09:37 AM   #135
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So much fun, so little time.....
Isn't that the truth
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Old 09-22-2006, 03:33 PM   #136
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To add fuel to the fire, here are the USDM 2007 STI Limited AVCS maps:

http://freon.shackspace.com/car/ecu%...-lim-AVCS1.png
http://freon.shackspace.com/car/ecu%...-lim-AVCS2.png

They've changed quite a bit from the 04-06. Interesting to note there are two different maps. All the other models (any market) always seem to have two identical maps. I can only speculate as to when each map is used or what determines the switchover. I'd guess IAM or something with throttle. Or one might not be used at all.

I've played a bit with my map. Following #125, you'd have to assume that if your boost and RPM are the same and your load/airflow go up by a modifcation to your AVCS map, you've increased your VE. I'm not sure wastegate duty is the greatest thing to look at. Most of what I've played with has with low RPM spool up. With enough data I can at least attack it statistically and try to relate intake cam advance to the load I get at a given boost and rpm. I'm not sure WGDC is that great of an indicator. I'd rather use boost.
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Old 09-22-2006, 03:39 PM   #137
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The new Legacy has that i-drive nonsense in it. I'm wondering if the more aggressive profile is for the more aggressive drive mode. My friend has one- I'll try to get some logs. I know I remember seeing that it was running 3 (yes 3!!!!) degrees of timing at peak torque. I was pretty shocked.

Mike
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Old 09-23-2006, 04:46 PM   #138
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Quote:
Originally Posted by Freon View Post
To add fuel to the fire, here are the USDM 2007 STI Limited AVCS maps:

I can only speculate as to when each map is used or what determines the switchover.
My guess would be the 2 different emission levels... Federal and California...
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Old 09-23-2006, 06:23 PM   #139
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I think the 2 AVCS maps are for the intake and exhaust, since the STI is now coming w/ dual AVCS

The avcs-2 looks like the intake, while the first one is the exhaust.
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Old 09-24-2006, 01:30 AM   #140
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Quote:
Originally Posted by west_minist View Post
I think the 2 AVCS maps are for the intake and exhaust, since the STI is now coming w/ dual AVCS

The avcs-2 looks like the intake, while the first one is the exhaust.
since when?
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Old 09-24-2006, 01:43 AM   #141
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I haven't been keeping tabs, but I think from 04. I know the 06 have it. This for the JDM.

Do the USDM STI not have dual avcs since 04?
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Old 09-24-2006, 02:15 AM   #142
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USDM 2.5L engines from 04-06 certainly do not have dual AVCS, just single on the intake cam.

The 07 STI I saw last week had several changes. Airpump like the 06 WRX, and I believe no TGVs (I couldn't spot a single wire going into the TGV housings). Obviously they revised the engine package. Dual AVCS is a possibility... I'll try to take a look next time.
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Old 09-24-2006, 06:15 PM   #143
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Quote:
Originally Posted by west_minist View Post
I haven't been keeping tabs, but I think from 04. I know the 06 have it. This for the JDM.

Do the USDM STI not have dual avcs since 04?
JDM STIs do not have dual AVCS yet...I have an MY06 JDM STI Spec C and it definitely only has AVCS on the intake...

The new MY07 JDM Legacy may have dual AVCS, not too sure...
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Old 09-24-2006, 07:05 PM   #144
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ok. Thats good to hear
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Old 09-24-2006, 10:22 PM   #145
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a bump for my earlier question has anyone had any luck making avcs work with a aem management
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Old 09-25-2006, 07:07 PM   #146
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Originally Posted by AZScoobie View Post
Good post David.

Side note.. The Cam wheels stop at 30 degrees. Dont bother using huge values.. They will only go to 30. The JDM V8s go to 40.

Clark
If in-fact has been posted above is from an 07 USDM STi then either Clark is wrong or they changed something...there are 30+ degree advance values in that table...
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Old 09-25-2006, 07:14 PM   #147
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Just something to ponder on...

If in fact as some claimed or think the overlap would allow the charged air (much cooler than exhaust) to blow through into the exhaust and that would "spool" the turbo more or make it spin faster (or increased boost etc):

1. My understanding was that it was mainly the "heat" that spun the turbo mostly (the actual gas pressure next). Wouldn't you think then the much cooler air from the intake side would actually hurt this? This is not a corn mill turbine in the river where if you had more water flow it would spin faster or a windmill...

2. Everyone agrees that the pressure in the exhaust manifold is much higher than the intake manfiold. With negative pressure ratio there wouldn't be flow.

Hey I'm not saying I know anything and both statements could be fundementaly stupid or wrong ...but something to think about.

cheers
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Old 09-25-2006, 07:32 PM   #148
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Quote:
Originally Posted by keyser_soze View Post
If in-fact has been posted above is from an 07 USDM STi then either Clark is wrong or they changed something...there are 30+ degree advance values in that table...
I honestly have not spent time with the 07 STI. It might be changed. I do know that Even if you put 40 degrees in an US STI you will only get 30-32 degrees of advance. On the JDM V8's I can get 40 max. Once I work with an 07 STI I can report back.

Clark
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Old 09-26-2006, 05:30 AM   #149
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Clark
The gains you have been seeing, are they with bigger turbine housings?

TMS
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Old 09-26-2006, 12:53 PM   #150
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I have three maps I currently use... One for stock turbo.. Nice gains out to redline... One for Green sized bolt ons which helps bottom end alot and the last 1000 rpm. One for Big turbos like 35R which shows gains all through the pull.

Clark
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