Let's talk AVCS tuning.....anyone...?

[TMessick]

I'm not convinced that additional airflow necessarilly corresponds to additional flywheel torque in this case. Under high overlap with moderate/low backpressure and boost, it's possible to over-scavenge the engine. Basically, you use the positive pressure in the intake to blow out the charge and also help spool up the turbo during the overlap since both the int. and exh. valves are open. In fact, this is one of the advantages of VVT and turbo as it can result in greatly reduced turbo lag and can actually net negative pumping work on the exhaust stroke.

However, in this case, you end up dumping some of the total engine airflow straight out the exhaust. As such, it does not contribute to the amount of air/fuel trapped in the cyl during the compression/expansion strokes. Since opening the intake early also means closing the intake early, at some point, you're sacrificing the ability to trap as much air as possible in the cylinder (optimum trapping efficiency) for the ability to keep the turbo spinning. Note that running high overlap during light boost will definitely help spool, but the added airflow does not necessarily mean you're making more torque...

Just throwing that out there -- feel free to disagree, argue, call my statements blasphemous, ...

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[bboy]

Originally Posted by TMessick

I'm not convinced that additional airflow necessarilly corresponds to additional flywheel torque in this case. Under high overlap with moderate/low backpressure and boost, it's possible to over-scavenge the engine.

Naturally aspirated I would agree this is more possible, but with a turbo blocking the path, I think it's unlikely.

I've done a whole lot of reading since I started this thread and a whole lot of camshaft analysis.

In my opinion the best way to think about AVCS is that by advancing the intake cam at low RPM, you are closing the intake cam earlier. When the intake cam is closed earlier, the piston has more time and distance to compress the air in the cylinder. Thus AVCS essentially alters the dynamic compression ratio at low to mid RPM. As RPM increases, the momentum of the air (velocity) has more of effect, filling the cylinder better. At high RPM the cylinder is filled with more air by closing the intake cam later than it would be if AVCS had advanced it. The key concept is more air.

For me, AVCS is all about VE. At low RPM when the cams kind of suck, AVCS increases VE (pumping efficiency) and at higher RPM keeping the air's momentum trumps the AVCS's effect (which acts to stop flow as the intake valves shut).

AVCS improves spool because more air is trapped at low-mid RPM in the cylinder and it compressed more, burned more thoroughly, and burns hotter. Bingo, more gas, hotter gas, faster spool, more boost, more torque.

Another way to look at it is from the exhaust dilution perspective like TMessick is doing. AVCS closes the lobe separation angle increasing the overlap. This acts to blow more exhaust out of the cylinder at TDC becuase the intake charge rushes in, blowing the last remenents of the exhaust out. Less exhaust dilution, means more pure air can enter the cylinder. More pure air, plus more compression (early intake valve closing) makes for a more efficient air pump (increased VE).

So what about using AVCS at high RPM? Well the data you guys have posted argues against it. Mass air flow is asymtopically approaching the 0 degrees curve after about 5500 RPM. That may be an effect of the turbo being used, not air flow, but let me argue it another way. If you look at forced induction engine as just a normally aspirated engine operating at serveral leagues below sea level, then the same camshaft principles should apply as they do to NA cars. At high RPM it is duration that wins the day. AVCS does nothing to increase the duration. To make more power at high RPM you need to have those cams holding the valves open longer not just increasing the overlap. The overlap helps with velocity, but RPM has done a great deal to help that already without AVCS, what you need now is the cams to take bigger bites of air, and that means more duration.

[crazymikie]

Has anyone looked at intake pressure and exhaust backpressure with respect to AVCS? I'd be interested to see how the intake/exhaust pressure ratio relates to AVCS tuning.


Mike

[thejean]

Ok, now you guys got me searching for JDM heads.

[AZScoobie]

Originally Posted by crazymikie

Has anyone looked at intake pressure and exhaust backpressure with respect to AVCS? I'd be interested to see how the intake/exhaust pressure ratio relates to AVCS tuning.


Mike

I have.
It simple hookup to your uppipes EGT bung.

Clark

[crazymikie]

Originally Posted by AZScoobie

I have.
It simple hookup to your uppipes EGT bung.

Clark

I actually had a setup in my car with this- It was pretty interesting. I just need to find a volunteer with an STi

Thanks,
Mike

Oh yah- for anyone else that's going to attempt this- make sure to use some tubing that has compression fittings, not ones that are welded on....OOPS.

Some 1/8" copper tubing works nicely. They sell it at Autozone with the compression fittings.

[west_minist]

Not the best. Today was a disaster for my colleague on the Dyno. The Dyno guy did not save all of the runs per AVCS. Also re ran out of time. The guy owes him a coupls free passes

http://socob.bb/forum/viewtopic.php?p=677

[Freon]

Originally Posted by TMessick

Under high overlap with moderate/low backpressure and boost, it's possible to over-scavenge the engine. Basically, you use the positive pressure in the intake to blow out the charge and also help spool up the turbo during the overlap since both the int. and exh. valves are open.

I suppose it is possible. I also look at VE / (MAP / Atmospheric pressure) . This should probably not exceed 1.0.

I haven't gotten too aggressive with it yet so I haven't seen this, but I wonder if you'd see AFR spikes like a misfire on the wideband.

If nothing else, the technique of maximizing airflow does bring boost up faster looking at time, and lowers boost threshold. I can get to load areas and RPM where I'm not messing with AVCS much faster, and certainly that is making the car faster.

I can't say I've seen anything to indicate this is happening, but it could.

[thejean]

I have already decided that as soon as I can afford to, I am going to buy some JDM AVCS heads to use with my S2 block. Autronic SM4 will control it all. I think I need to think about the tranny before I do that though. I'd like to do that now while I have the car apart but time and money are limited.

[AZScoobie]

THey need to be on one sheet if possible. It woudl be much easier to read. THe big problem with this test is that once you change the dynamic compression of the motor you change the point in which ignition is needed. You also effect the VE of the motor so you must alter the AFR. This is why a simple AVCS remap can take hours and hours and hours. You need to tune timing, AFR and Cam in 1000 rom increments all the way up. Thats the only way I found so much damn power. When I was done, I was tired, I had a headache that was head splitting, The car was downright tired, I burned a tank of gas... but I had an incredible curve.

Then take that AVCS map and toss it on another car with another set of parts and realize that it is not correct... This is why I have developed yet another map that makes gains on every Car. I really just need to know the turbocharger being used.

NON STI 2.5s with AVCS are very different in tuning AVCS. I have yet to find huge power gains with these models. Some power yes, Some response yes. But I can tell you they do not like MORE advance.

The JDM Engines are gain very different with what works best. On a GT35R JDM 2.0 I found an instant and shocking 40!whp at 30 psi runs by tuning AVCS. I think the reason is that I was able to put the compressor back on its map.

Side note.. I Do NOT suggest you run that much advance all the way out. Its very dangerous to the engine. I have attemped this before. Use your head when tuning AVCS. Listen.. If the motor is struggling let out. Listen for the tone of the motor.. you are changing a Huge dynamic.

Clark

[thejean]

Oh, no worries, I wont be tuning it.

[west_minist]

On the JDM, the AVCS goes to zero automatically after 6000rpm.. This is regardless if it is 10 or so.

Thanks you very much for your input Clarke. It is alway appreciative.

We were very curious to see the what avcs would do on a premade map.

Test were limited to 6-7k max.

But now that we have partial data, we can not go back and see how afr and ign affects the tune. At present, we are awaiting an LC1. So any changes would be limited to the spool up area until the LC1 arrives.

[crazymikie]

Originally Posted by AZScoobie

NON STI 2.5s with AVCS are very different in tuning AVCS. I have yet to find huge power gains with these models. Some power yes, Some response yes. But I can tell you they do not like MORE advance.

Clark

Do you speculate this has to do with the tiny turbo, or more specifically, the tiny turbo exhaust housing?


Mike

[west_minist]

Finally. I receive good support from EcuEdit.

I could not delete my post above.

I was able to merge all the logs together.

AVCS=0
AVCS=10
AVCS=20
AVCS=30
AVCS=40
AVCS=45

Manifold Relative Pressure Corrected (PSI)


Mass Air Flow (g/s)



Engine Load (g)



AFR



AVCS



WTQ



WHP

[west_minist]

Update above.

[AZScoobie]

I think its going down up top because of the oil pressure going from 20 to 100 psi over the rpm range. Its not enough duty cycle to get it to hold up top. This is good data. It only confirms what I have found. However. Now you need to tune the car at those AVCS numbers. This way you can have HP and trq numbers for each setting. This is the way I did it. Only I did it in 1000 rpm increments from bottom to top. I ended up with a curve I liked. Last week I tuned a dozen cars. I had an STI with a Green. I dropped in my cam map and made 15 whp across the power band and 20 up top. These are typical gains for mapping AVCS.

Clark

[west_minist]

AVCS maps was release to the owner. My only wonder is, since the AVCS=50 was not tested, how high the AVCS can go.

My STG1 and STG2 runs 45 low in the rpm, so this AVCS was not really good to really compare stock, but for me, I am curious on higher valuse up to 4500rpm.

One of the members on my site that takes part in rally in England, also told me that AVCS is max and ign anf uel high when ALS is on.

As anyone can see, the AVCs open high up in the RPM really keeps the turbo spool. It would be nice to have this when shifting

Again Clarke, thanks for the feedback. I am happy to be one of a few who have done it and post the results. The Evo Mivec stuff got me think of performing the same test and so I did.

As soon as I can confirm AVCS greater than 45, then we will test with ign and fuel.

[AZScoobie]

In my experience I have seen max of 40 to 42 on the JDM Cam gears and 30 to 32 on the US cam gears. The stops are different. I dont have a need to go that high anyways so I dont think its that much of a big deal. Your cars in your market may act differently. My thought is that if you max the map out you are just making the diaphrams work harder with all that oil pressure agains the stop. I have seen bad AVCS cam gears.

By the way.. After a reset ECU start the car and let it idle untl the cams go to 0. If you dont have a data logger let it idle for 2 min. If you start the car and take off the AVCS cam alignment will not happen during the pull. I have driven cars for 20 to 30 minutes only to find the cams are not aligned. Pulling to a stop allows the Alignment to happen.

Clark

[west_minist]

What we do here, after a reset, drive normal (slowly) with increasing acceleration going thorugh the gears. it takes about 10secs. It works for all the JDM models.

[cdvma]

Awesome graphs, thank you.

[bboy]

From those data it looks like you could improve things by leaning out the fuel with AVCS advanced since the mass air is greater than the AFR would lead you to believe (fuel is burning more efficiently, you need less fuel), but the main effect is still between 2000 and 4200 RPM and then the cams favor duration to just overlap. Dyno data is still key. These are great experiments.

[west_minist]

It is. The key really, I guess, is using the 1000rpm increment clarke talks about.

I do not know why the Boost graphs does not come up, but you are correct. The AFR needs leaning a bit in low rpm.

I think it is good data for those with JDM models to perform the same test for comparison and take it from there.

I do not have an STI or WRX to perform these test continously. I am curious how the JDM WRX will behave with AVCS, since the max AVCS is 33 in the maps.

I have an NA model with AVCS, but the ecu is Denso and I cannot tune it. Not to worry, the Hydra is coming

[west_minist]

Update: Finally. I receive good support from EcuEdit.

I was able to merge all the logs together.

Please see above or here:- http://forums.nasioc.com/forums/show...&postcount=189

[Airboy]

Haven't seen much on the '06 WRX so I went out and collected some data.

First , some info on the test:

Sequence:
1) Program map into ECU (IAM set to 1.0 on reset)
2) Drive car on side road to lower IAT (engine heat during reflash)
3) Start log at the same spot on the road
4) Log three consecutive runs (noting starting points along the road)
5) Return to side road and program new map
6) Repeat (2) to (5)

The maps used are identical except for the AVCS map. I used three maps but to keep things easier on the eyes, the plots below does not show the intermediate case.

In the plot legion, 20deg 1 means 20deg AVCS map, run #1

First up, AVCS: the map has 12.5* but I guess the logger or the ECU rounds up.


Next, Boost: Not much difference


Then WB AFR: Not much difference


Then, Engine Load: consistently higher with more AVCS advance.


The next set of data is sort of how efficient the engine is in pumping air. It is calculated as the (Manifold Absolute Pressure)/(Engine Load). The lower the number, the less boost is required per gram of air going into the engine. I think/hope that is the correct interpretation.

[west_minist]

http://socob.bb/forum/viewtopic.php?p=759

AVCS testing was done on a completely stock MY06 ADM STI.
http://socob.bb/forum/viewtopic.php?t=226

I am not too happy with the data. The environment was not controlled enough and the logger decided for some unknow reason to change the logging format.

AVCS @ 0
AVCS @ 10
AVCS @ 20
AVCS @ 30
AVCS @ 40 Color=Grey
AVCS @ 50

MAF



Engine Load



Boost



AVCS



AFR



Intake Temperature