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Old 09-06-2006, 01:32 AM   #51
SlickRick51586
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Quote:
Originally Posted by Element Tuning View Post
Always worth testing something new but.....advancing the intake cam timing typically reduces the length of time for the fuel and air to burn. By retarding the exhaust cam you lengthen the amount of burn time. This is a good thing as it allows for more complete combustion. This is already a big problem with our motors and results in having to run lots of ignition timing. Earlier intake cam opening and later exhaust cam timing lengthens the burn window. Once you put boost into the mix then you have to be careful not to blow your intake charge out the exhaust valve and this can be tricky. This is typically why you can advance a lot at low boost but not so much at high boost or high rpm.

Thanks,
Phil
http://www.elementtuning.com
I think the interrelation between everything needs to be taken into account.
AVCS makes for better VE at low RPM which is agreed upon (at low rpm more duration and overlap generally means more pressure but less airflow). At higher rpm don't you generally get a faster more complete burn? One would think that more advance on the intake stroke (by using AVCS) even at higher RPM would yield more torque as long as the AFR stay in the right range. The problem being that as soon as you use advance, it would change your AFR, and MBT, correct? Phil might be getting a better VE by changing other values than the AVCS at higher RPM. I'd love to see some of Clark's and Phil's maps...


(added)
A lot of it might have to do with treading that fine line between blowing out your fuel on the change between exhaust and intake stroke. I think this is what AVCS would help the most by keeping all the other variables the same and then adding a little AVCS here and there lets you maximize your VE.


I really don't know more about my next question...
Is AVCS making a difference by changing intake pressure/compression?
I say this because I have read posts saying it helps low end and can make a larger difference around turbo spool/midrange torque. Would it be correct to say more duration results in higher pressure? which I *think* would be kind of like how having a higher compression motor can spool a turbo faster.

Adding to this...

Before a turbo starts or begins to make boost/flow how much of an intake restriction is it?

I don't want to get to far off topic, especially since I could be making myself look stupid, but a few more questions...

If a turbo is a restriction (pre boost) then could that be one reason why AVCS makes such a noticeable difference?

Would AVCS make less difference on a higher flowing turbo because of the fact that overlap or just increased intake duration increases pressure but reduces flow?

I'm not sure on all of my facts. I'm just trying to learn...
Hopefully my questions are constructive so that we can learn more about AVCS (This is my please don't flame me Post Script)...
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Last edited by SlickRick51586; 09-06-2006 at 02:16 AM.
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Old 09-06-2006, 10:30 AM   #52
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Originally Posted by crazymikie View Post
Ken-

I've found that you can make great power on STi's with very little timing advance. On a stock turbo, after remapping AVCS, with only 10-11 degrees of advance at peak torque I was able to make nice power.

Compare that to a 2.0L where I was running 15 degrees of advance on my stock turbo.
the low advance necessary to net you good torque shows the VE is high and the engine is breathing well. nice job!

as it's been getting cooler out i have dropped my advance at peak torque a bit, which is around 3500rpms. i now run about 12.5 degrees there, and immediately start ramping up with rpm. boost is 24.5psi and tapers to 20 at redline.
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Old 09-06-2006, 10:41 AM   #53
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Originally Posted by ride5000 View Post
the low advance necessary to net you good torque shows the VE is high and the engine is breathing well. nice job!

as it's been getting cooler out i have dropped my advance at peak torque a bit, which is around 3500rpms. i now run about 12.5 degrees there, and immediately start ramping up with rpm. boost is 24.5psi and tapers to 20 at redline.
sounds close to what i have going on with the 16g- what kind of timing do you see at redline?
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Old 09-06-2006, 10:54 AM   #54
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somewhere around 23-24.
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Old 09-07-2006, 03:46 AM   #55
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Removed timing question, too off topic!

Great AVCS info!

Last edited by xolosis; 09-07-2006 at 11:06 AM.
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Old 09-07-2006, 05:15 AM   #56
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Let's not forget that the difference in USDM/EDM/JDM AVCS maps may be due to differences in the centerlines of the intake and exhaust cams between the various designations. For example, I had my JDM Spec C camshafts profiled and degree'd, and the intake centerline with 0 advance is 132 ATDC and exhaust centerline is 105 BTDC. I'll bet the USDM/EDM engines are less agressive than this, probably more like 120/113 for intake/exhaust. This of course would mean 0 degrees of advance on a JDM STI is likely more retarded than 0 degrees of advance on USDM/EDM.

Here's the profile...
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Old 09-07-2006, 09:01 AM   #57
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Originally Posted by STI8U View Post
Let's not forget that the difference in USDM/EDM/JDM AVCS maps may be due to differences in the centerlines of the intake and exhaust cams between the various designations.
W00t. Somebody finally said it. There are cam differences between the motors so that does play a roll in the overall AVCS utilized.

In an NA motor you actually want overlap at high RPMs. It helps pull in the new intake charge. Turbo motors are different. However, what Clark *might* be talking about is that the USDM STI boost drops dramatically because the turbo becomes less efficient. AVCS in that area could actually help to create more power. If the stock turbo didn't drop off then keeping AVCS low or zero would be the best bet. However, the stock turbo DOES drop off.

BTW - this is one of the better AVCS discussions so far. It's always helpful when tuners post and start disagreeing because more information is posted. I guess it's time to start increasing AVCS as the turbo gets more inefficient.

t
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Old 09-07-2006, 11:53 AM   #58
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W00t. Somebody finally said it. There are cam differences between the motors so that does play a roll in the overall AVCS utilized.

In an NA motor you actually want overlap at high RPMs. It helps pull in the new intake charge. Turbo motors are different. However, what Clark *might* be talking about is that the USDM STI boost drops dramatically because the turbo becomes less efficient. AVCS in that area could actually help to create more power. If the stock turbo didn't drop off then keeping AVCS low or zero would be the best bet. However, the stock turbo DOES drop off.

BTW - this is one of the better AVCS discussions so far. It's always helpful when tuners post and start disagreeing because more information is posted. I guess it's time to start increasing AVCS as the turbo gets more inefficient.

t
Look at some of the boost profiles and AVCS maps for the JDM cars- boost tapers immediately, but I'm guessing that torque doesn't. I'm guessing that by modifying AVCS and changing the VE of the motor, the turbo can run less boost and still make just as much power.

Anyone have any dyno runs of a v7 motor stock?

Mike
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Old 09-07-2006, 08:00 PM   #59
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This is all great theory. The Cam Profile shows alot. I see alot of you guessing. Try using a Dyno to see what works best.

Clark
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Old 09-08-2006, 03:14 AM   #60
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I just got my car back today, after it was found my so called AVCS aftermarket cams were actually non-AVCS cams. Anyway, the cams have been fixed and are now moving as expected.

I haven't had a chance to do detailed analysis, but what I found was quite interesting. The car has been tuned with the cams at a fully retarded position of ~130 crankshaft degrees (as reported by the camshaft position sensor).

I chucked in 110 degrees (~20 degrees advance) across the entire map (I have Autronic EM) and this is what happened:

1. Car was running much leaner - hitting peak boost the car was running 11.5:1 AFR with cams at 130 degrees. With the cams at 110 degrees, car was running 13.5:1 AFR - didn't let it rev past 4000RPM for fear of blowing the engine.

2. Turbo spooled up faster - previously hitting 15PSI @ 3600RPM in 3rd, now hitting 15PSI @ 3200RPM in 3rd. How lean the car was running probably aided the spool up time.

What I believe this shows is with 110 degrees advance, at the RPM range I looked at (2000-4000RPM), the engine was flowing significantly more air, hence this level of advance is much more optimum for that range.

An idea I now have for tuning AVCS without a dyno is:

1. Set AVCS map to 0 advance. Tune fuel map rich - e.g. 10.5:1 for high load sites.
2. Set AVCS map to 5 advance. Do a few power runs, log AFRs
3. Set AVCS map to 10 advance. Do a few power runs, log AFRs
4. Set AVCS map to 20 advance. Do a few power runs, log AFRs
5. Set AVCS map to 30 advance. Do a few power runs, log AFRs

Once you are done, compare the AFRs at various RPMs. The leaner the AFRs become relative to your first run the more optimal (since the fuel map is constant for each run, the AFR reading shows how much more/less air is going into the engine). Doing the base run rich is to avoid running too lean during your testing. Running it at 10.5:1 allows for you to detect if the engine runs richer (most wideband AFRs lose resolution below 10:1).

The above technique I believe should work with a MAP-based engine management system (like Autronic or Motec), not sure on a MAF-based system as load is expressed in air mass. On a MAF-based system it might be as simple as looking at the MAF readings for each different level of advance but it's kinda chicken in egg.
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Old 09-08-2006, 01:22 PM   #61
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More advance will increase the VE in those ranges as you found out. Good luck. This is going to be very difficult without a dyno. You have no airflow reference. Only AFR to go off of.

Clark
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Old 09-08-2006, 02:16 PM   #62
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Quote:
Originally Posted by STI8U View Post
I just got my car back today, after it was found my so called AVCS aftermarket cams were actually non-AVCS cams. Anyway, the cams have been fixed and are now moving as expected.

I haven't had a chance to do detailed analysis, but what I found was quite interesting. The car has been tuned with the cams at a fully retarded position of ~130 crankshaft degrees (as reported by the camshaft position sensor).

I chucked in 110 degrees (~20 degrees advance) across the entire map (I have Autronic EM) and this is what happened:

1. Car was running much leaner - hitting peak boost the car was running 11.5:1 AFR with cams at 130 degrees. With the cams at 110 degrees, car was running 13.5:1 AFR - didn't let it rev past 4000RPM for fear of blowing the engine.

2. Turbo spooled up faster - previously hitting 15PSI @ 3600RPM in 3rd, now hitting 15PSI @ 3200RPM in 3rd. How lean the car was running probably aided the spool up time.

What I believe this shows is with 110 degrees advance, at the RPM range I looked at (2000-4000RPM), the engine was flowing significantly more air, hence this level of advance is much more optimum for that range.

An idea I now have for tuning AVCS without a dyno is:

1. Set AVCS map to 0 advance. Tune fuel map rich - e.g. 10.5:1 for high load sites.
2. Set AVCS map to 5 advance. Do a few power runs, log AFRs
3. Set AVCS map to 10 advance. Do a few power runs, log AFRs
4. Set AVCS map to 20 advance. Do a few power runs, log AFRs
5. Set AVCS map to 30 advance. Do a few power runs, log AFRs

Once you are done, compare the AFRs at various RPMs. The leaner the AFRs become relative to your first run the more optimal (since the fuel map is constant for each run, the AFR reading shows how much more/less air is going into the engine). Doing the base run rich is to avoid running too lean during your testing. Running it at 10.5:1 allows for you to detect if the engine runs richer (most wideband AFRs lose resolution below 10:1).

The above technique I believe should work with a MAP-based engine management system (like Autronic or Motec), not sure on a MAF-based system as load is expressed in air mass. On a MAF-based system it might be as simple as looking at the MAF readings for each different level of advance but it's kinda chicken in egg.
Another trick I've used is to look at how much dynamic advance the car is running vs the power output. You can see how long a pull takes or else you can use a road dyno. If modifying the AVCS map results in less dynamic advance but the same or greater power output, then you are doing the right thing

I wish I had access to a dyno to test things. Maybe we should all take a trip out to visit Clark
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Old 09-09-2006, 01:52 AM   #63
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Originally Posted by AZScoobie View Post
More advance will increase the VE in those ranges as you found out. Good luck. This is going to be very difficult without a dyno. You have no airflow reference. Only AFR to go off of.

Clark
I can use the factory MAF and log the 0-5V output from the MAF to my Autronic. I have the MAF scaling table from the factory ECU so I could easily interpret the values, although I guess I'm looking for increases in airflow, not quantitative values.

Would the MAF be a suitable airflow reference?
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Old 09-09-2006, 07:49 PM   #64
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Stage 2 STI.

Today I tried ...
20d AVCS @ 4800
15d AVCS @ 5200
10d AVCS @ 5600
10d AVCS @ 6000
10d AVCS @ 6400
5d AVCS @ 6800

MAF voltage was slightly higher (0.02-0.04) with AFRs slightly leaner (0.1-0.2). FWIW, I am running an APS 70mm MAF. I went back to my original map and MAF voltage was back to normal. Went back to the aggressive map and MAF was slightly higher again and AFR was slightly leaner again.

Overall, the car didn't feel that much different so I'm with clark on needing a dyno (lol).

One thing I did notice. Boost was more easily attained with higher AVCS. WGDC was lower for the same boost. Seems like the car was more volumetrically efficient

Oh, for reference my previous settings were ...
18d AVCS @ 4800
8d AVCS @ 5200
0d AVCS @ 5600
0d AVCS @ 6000
0d AVCS @ 6400
0d AVCS @ 6800

Load has been left out on purpose for simplicity. Assume this represents the load area that my car was running in.

t

Last edited by WolfPlayer; 09-09-2006 at 07:55 PM.
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Old 09-09-2006, 10:32 PM   #65
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the shift in afr is interesting since it is a maf based system, and it indeed picked up the extra air as evidenced by the voltage change.
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Old 09-09-2006, 10:57 PM   #66
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This is an interesting thread...

The one thing that I see lacking in this thread is the theory of why it is there in the first place.... And what we can do with it to gain power...

The reason that it is there, is to control nitrogen oxide emissions...

For years engines had an EGR valve to control nox emmissions, but that has been replaced by phasing the cams...

But what exactly are they controlling with the cam phaser???

To make it real simple, they are controlling the temp of combustion...
You might ask how this is done with just a cam phaser...
It works the same way the old egr valve did, it allows exhaust into the cylinder...
Instead of letting it into the intake, it uses the overlap to leave it in there...

So the real question would be... How can we use this to make more power???

Lets look at how it is mapped...


Look at all of the "20" blocks... They are all heavy load, low rpm...
The same area you need an egr to work or it will ping like crazy under heavy load...

Now look at what Clark pointed out, there isn't anything on the upper part of the map above 5200 rpm... Guess why??? There are zippo IM test that are done at 5k, and why make it make anymore hp stock... It is allready 300......

The point I need to make is that this has more potential than most people realize... The bottom part of the map is allready based out from the factory for IM and controlled combustion temps...

The top end of the map is what we are interested in to make power...

If I had a dyno I know how I would go about tuning for power with this setup... I might not be correct, but I think I would be close...

Now, how to make power with it, and a turbo...

Start with about 11 to 1 afr, and keep it there all the time... for all of the runs... run fixed timing, same boost, etc
Map EGts as close to exhaust valve as possible, there is a reason for being close to the valve...
Using the high load column, find number for each cell that drops egt 200-300 degrees... It will basically be overlap blowthru doing the cooling...
Now smooth the map out and go from there...

Now before anyone flames me about this...

I used to do blower engines sort of this way by changing rocker arm ratios and clearances to find the optimum blow thru to develope a desired cam choice, those new grinds always made more power than the old ones...

With AVCS you can do a lot of playing, without ever opening it up.....

I guess the main point I am making here is that you have to find the optimum blow thru for your setup... Worry about everything else after you figure that out...

After all, engines are air pumps... Make them pump air... If they don't like it, force feed them....
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Old 09-11-2006, 03:11 PM   #67
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Good post David.

The Thing I want to make clear as to help you guys is that in changing Cam timing you are changing the running compression of the engine. This means that the AFR and timing settings are no longer optimal. That is assuming that you guys are running the optimal settings... Which 90% or more are not.

The reason why this is important is that in some cases changing the timing might really help you when that setting really hurts others.. So you need to develop a system to adjust, Cam, AFR, Timing and boost to find out what works. This is why it took me 4 hours of dyno tuning straight to find out what works well. When you change your VE you need to change your timing and AFR.

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
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Old 09-11-2006, 07:06 PM   #68
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Has anyone noticed a sound associated with over advancing AVCS, kind of a flutter. Anyone speculate on what that sound is? I'm thinking the cam is slipping backwards after the solenoid advances completely.

Clark-so advancing the intake cam and increasing VE is to to an increase in dynamic compression ratio?
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Old 09-12-2006, 07:13 AM   #69
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Quote:
Originally Posted by bboy View Post
Has anyone noticed a sound associated with over advancing AVCS, kind of a flutter. Anyone speculate on what that sound is? I'm thinking the cam is slipping backwards after the solenoid advances completely.

Clark-so advancing the intake cam and increasing VE is to to an increase in dynamic compression ratio?
What RPMs is the flutter at - could be compressor surge if your turbo is spooling too fast...
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Old 09-12-2006, 12:08 PM   #70
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Agree. It might be compressor surge.

Clark
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Old 09-12-2006, 12:57 PM   #71
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I guess it's possible, but it does not sound like surge to me. Surge is more of a honking noise.

This begins to occur at light to medium throttle, ~4000 RPM and slight vacuum (10-50 mm Hg). I know it's related to AVCS because when I turn off the solenoids the sound disappears. Also if I lower the advance in the AVCS map the sound disappears.

I have many fears about why I'm getting the noise, but right now I'm just trying to figure out what the hell is making it.

If you have ever listen to a motor thru det cans that's what it sounds like. It's as if someone opened a little window on the valve cover and all the sudden you could hear the valves better. It's not loud. It a pffft,pfft,pfft,pfft or a thfft, thfft, thfft, thfft that increases exactly with RPM and it's dependent on active AVCS.

To get rid of the noise I need to retard the AVCS substantially, like 1/3 less advance. It began making this noise after a rebuild with higher compression pistons. I tuned out the noise, but I am still wondering what the hell it is + I'm looking for a cause (e.g. is it a indication of lowered oil pressure? I'm getting gauge).
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Old 09-12-2006, 01:08 PM   #72
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Quote:
Originally Posted by bboy View Post

It began making this noise after a rebuild with higher compression pistons.
Less dish in the piston?
Valves hitting piston?

TMS
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Old 09-12-2006, 01:12 PM   #73
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I doubt it. It better not be. The valve relief slots are there to the same depth as stock.
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Old 09-14-2006, 04:07 PM   #74
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I just wanted to restate that I have done a few more AVCS tests and the difference in boost at WOT in the upper RPMs when running positive AVCS values to redline is significant. I have had to retune my upper RPM WGDCs due to overboosting. Lots of STIs just run maximum WGDCs in the upper RPMs to milk as much boost as possible (because it seems to let off at 15psi anyhow). With increased AVCS settings, I hit 17.5psi at 6400rpms. Yes, I know that I do not want to do this - rofl. Just stating the results of a test. This wasn't boost creep either. I'm talking about boost in 3rd gear and my car has never creeped in 3rd gear (especially in 80+ d weather). I now have to clamp down my WGDCs a lot tighter in order to not overboost (as in the rofl AVCS test with 17.5psi).

t
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Old 09-14-2006, 04:09 PM   #75
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Quote:
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With increased AVCS settings, I hit 17.5psi at 6400rpms. Yes, I know that I do not want to do this - rofl.
t
Wuss :P
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