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Old 02-14-2013, 01:40 PM   #26
LittleBlueGT
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Also anxiously awaiting new EFR data.
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Old 04-12-2015, 10:30 PM   #27
sponaugle
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Quote:
Originally Posted by Ziggyrama View Post
Bringing this thread back to life again.

This does not sound right to me. When you retard exhaust valve, you delay it's opening. How can the exhaust cam be at rest in maximum retard? If retarding the exhaust moves up the valve opening, that's called advancing, which is what is applied to the intake valve timing.
You are correct, that statement was incorrect on my part.

Fortunately the overlap graphs are correct as I did not make the same mistake in the excel spreadsheet.

As you mentioned, the ECU is able to add advance to the intake cam (opening and closing the intake valve earlier) as well as add retard to the exhaust cam (opening and closing the exhaust valve later).

As a result, more exhaust cam retard adds overlap, as does more intake cam advance.

I mentioned that the stock ECU keeps the car at around 20 degrees of exhaust cam retard, which based of the correct directionality means the exhaust cam is sitting at about 8 degrees ATDC. As you would expect that would mean just a bit of overlap even at high load/rpm. ( only 3 degrees ).

This does mean that if you were to take 08+ heads and cams and put them in say a 2004 STI with just intake AVCS control you would always have exhaust cams stuck at 12 BTDC, which means you would not get very much overlap even when the intake AVCS is at maximum.

None the less good find and correction on your part. I'll add a correction to the original top post so other people don't take away incorrect information.

Cheers,

Jeff Sponaugle
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Old 04-13-2015, 03:19 PM   #28
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Just thought I would chime in with some real world info. A friend of mine and I just got tuned a couple of days ago. I have an '07 sti and he has a '15. We have the same engine build by the same builder with the same internals, same fuel system, same turbos, and even the same e85 from the same gas station. While my car made 417hp - 410tq, his car made 405hp - 450tq. The tuner said the torque difference was soley due to the dual AVCS. A difference of 40 ft lbs is a huge improvement!
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Old 05-30-2015, 03:46 PM   #29
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Nice thread, keep it going

I have trouble understanding how retarding it would make more spool. Granted it would make more power as for completion of burn, but not spool up.
I imagine advancing (yes reducing the retard value) in the low rpm would aid spoolup as exhaust gasses gets to escape through the ex valves earlier.
I imagine you should also get less EX gas fighting to find its way back into the intake ports.

Last edited by JMlegacy; 05-30-2015 at 04:47 PM.
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Old 05-31-2015, 08:24 PM   #30
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Testing out my new settings today, this is what i did and what i assume:

1. My engine used to be able to see 17.5 psi at 3600 (vf34 Ej20X) in second gear, but i changed the bottom half for a block that seemed to have a slight dish in the pistons as opposed to the flatter ones from the EJ20X

2. For 1 year or more i could not get the car to spool like the first block did. Most i could get was 17.5 psi at around 43xx RPM. I also have trouble brake boost launching (I'm on an auto gearbox)

3. I assumed that my CR was lower and the valve timing was not efficient anymore, so i went over to Black Art Dynamics and simulated my engine specs. I noticed the lower CR engine with the same AVCS setting was netting lower cylinder pressures, lower fuel usage, etc. So i bumped it up until both engines were the same. Also lowered my EX retard to around 15. I assumed this would allow much of the exhaust gases to spool the turbo, and also prevent reversion which i do not want. To me the high EX retard in stock rom is a fuel economy + environment protection strategy.

4. Went back in my rom with that in mind, upped my AVCS to 30 degrees from 20 (yes, a brave move i know) and then tested it out. My new 17.5 psi RPM was 3,953rpm. 400 RPM sooner.

5. I then tried to brake boost. OMG. 18psi at 3,000 rpm and chipping tires.

AVCS, what can i say. It's so dynamic. Everything works as one. Compression ratio, turbo size, EX restriction, etc
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Old 05-31-2015, 08:29 PM   #31
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JMLegacy,

What you can do and it will be a little hard with conditions, show a few screen capture graphs of boost vs the CAMs changes.

Run more avcs on the intake and test around the exhaust.

Good work. Keep at it.

Last edited by west_minist; 05-31-2015 at 08:38 PM.
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Old 05-31-2015, 10:41 PM   #32
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Links:

Old AVCS settings

New AVCS settings


I highlighted my manifold pressure at 3500 RPM for comparison. Old setting was 7.5 psi, new setting 10.16 psi

3200 rpm 4 psi (old) vs 7.1
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Old 05-31-2015, 10:52 PM   #33
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I would run more advance but my builder said i should be careful as the pistons in this block he can't remember the valve relief was as deep as the previous block's pistons. So after hearing that I'm done. lol
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Old 05-31-2015, 11:53 PM   #34
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Here you go my friend. By the look of it, it seems you did a little tuning

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Old 05-31-2015, 11:56 PM   #35
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Nice graph yes i did. Old graph was some days ago, new graph was today.
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Old 06-01-2015, 12:23 AM   #36
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I just wanted to add some of my observations regarding dual AVCS since I have done quite a bit of tuning late last year based on the information that has been provided on dual AVCS.

Last year, based on the discussions at that time there has been some disagreement on which direction is retarding and advancing in the exhaust AVCS. I'm just going to call it the exhaust AVCS because the word retard seems to confuse people when it comes down to the exhaust cam lobe.

My observations seem to be the lower the exhaust AVCS value the later the exhaust opening. So a setting of zero on exhaust AVCS, opens the exhaust port at 32 BBDC while a setting of 40 on exhaust AVCS, opens the exhaust port at 72 BBDC.

Now, before people start saying I'm going in the wrong direction, listen to my observations. I tested value ranges at both extremes on my daily driver. I spend a lot of time in traffic so torque at low RPM is quite noticeable. What I found is that when I used the lower exhaust AVCS values, it was a lot easier to drive around idle speeds. Where as with the higher exhaust AVCS values I found a significant lack of torque around idle speeds to the point where I stalled quite a few times. All other non exhaust AVCS values being the same.

In theory, the longer the exhaust port is closed at low RPM the more torque the engine will produce because the combustion phase is pushing against the piston longer. This increased torque at low RPM is what I am observing on my car when lowering the exhaust AVCS value.

Last edited by Rallymon; 06-01-2015 at 07:10 AM.
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Old 06-01-2015, 08:25 AM   #37
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According to the technical manual of my EJ20X



I'm wondering, guys, do you think they got their wordings incorrect?
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Old 06-01-2015, 09:33 AM   #38
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STI 2.5
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Old 06-01-2015, 12:15 PM   #39
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In Cobb's ATR, I think the software's table name is somewhat misleading especially after conducting my AVCS testing and observations. I personally think they should have just labeled it exhaust AVCS. So increasing the AVCS exhaust value would be more intuitive to advancing the exhaust cam.

It works for me. Just thought I would share.

I did try what was mentioned earlier. Opening the exhaust earlier to spool earlier. Yes, it did spool at a lower RPM but my experience was that it took me a little longer to get to that RPM because of the lower torque. I also found it hurt my fuel economy somewhat. So I abandoned tuning for lower spool through AVCS.

I think this tuning strategy would be useful for a larger turbo, but with a VF size turbo I do not think there is much to gain.
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