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

[bboy]

OK. I'm the first to admit the theory behind AVCS in vacuum versus boost starts to make my head hurt.

What AVCS does seems to be fairly basic. The intake valve opening early and closing early (more advanced) results in cleaner air (less residual exhaust, scavenging) and some improvement in the charge velocity at mid-RPM. Both result in improved mid-range torque and the increase in gross air induction in the volume and velocity of exhaust, which results in quicker turbo spooling.

Tuning it however is not easily accomplished. The benefits of AVCS seem to be most prominent in the mid RPM range and "on boost". Here the induction is blowing the the last reminents of exhaust out through the still open exhaust valve. In general, in this region (say the window from 10-20 psi, and 3500-5000 RPM) more advance is better. Agree? Disagree? How can you tell?

Ultimately a dyno can tell you about torque output in those regions. Perhaps you could tune to maximum torque? Are the same settings that benefit torque also going to benefit spooling of the turbo?

Now lets turn to a more mysterious area of AVCS tuning: the vacuum load sites. Here there is a theoretical issue in that on the intake side pressure is very low and on the exhaust side pressure is likely higher. If the intake cam is opened too early (advanced by AVCS), then there is the potential for "reversion" of exhaust back into the intake. When to advance, and by how much to advance, in the vacuum sites, will be a trick. Again, what will be the tuner's guide? Torque would be best, but perhaps we could use AFR to some extent.

Some argue that little to no reversion occurs with more overlap (as is the case with AVCS advance) except at very low RPM, like idle. Other's blame the sluggish "big cam" performance at low-mid RPM exactly on the increase in overlap and exhaust gas dilution.

Another question of interest to me is how and in what ways might a larger turbo affect AVCS tuning?

Another might be: if overlap is king at high RPM, why do people routinely taper AVCS advance as high RPM is reached? Does this have to to more is velocity of air through the motor, and AVCS has done it's thing in teh mid range and is unneeded at high RPM. Perhaps the engine needs all the induction effieciency it can get at high RPM, and AVCS is somewhat of an inefficiency (lowering mid-range VE) despite it's torque gains.

Not many have tuned AVCS, but perhaps we can at least get things going here. Theory, empirical approaches, data.......anything people can post would be useful.

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[Uncle Scotty]

I've played with it a bit and take many small steps.

I've increased some numbers by up to 4* or 5* but ya can go backwards REAL quick and get some MASSIVE det if ya not careful

look for a thread by me on this started about 2 months ago

[bboy]

I'm sorry I missed the thread. Perhaps I should have bumped yours.

Yes detonation is at issue as well, but it always is. I'm assuming you saw detonation under boost. The combination of more advanced AVCS and less advanced timing could be very tricky to tune since they are working in opposite directions. Cylinder pressure increases with the AVCS advanced and "in boost", so you will have to retard timing to prevent detonation. From a tuning stand point, retarding your timing first and then adjusting the AVCS may be the way to go.

Another reason for an increase in detonation that I could also see is if your remained AVCS advanced up into high RPM and high boost, reversion might rear it's head as well, and more so because of the AVCS advance. That phenomena would only occur at a high boost threshold, and it would occure regardless of the AVCS, but it would be compounded by it.

Thanks for the post. I'll look for the thread.

[west_minist]

The question is in high rpm, you may have the precious fuel mixture being blow out @ high avcs. But is this good for the Antilag effect ?

I am assuming and think it is better to have it not advance in high rpm, since the boost is on.

I notice that the 2500-3000 range is a very critical range, even in non AVCS cars, seems to have a note of labouring.

I am assuming that in this area, AVCS could be less (I want to say more), but thats my thoughts.

I will have to see if I can get the STI I am tuning to play with different maps in that area. We have seen gains with different avcs setting in the high load maps, but nothing to really tune in certain areas, since all are road dynos and makes it very diffucult to see.

Also, please note all of this on a Stock OEM computer.

The JDM WRX AVCS map is different to the JDM STI map. Why? I am not sure.

The S20x (eg S202) and STI seems to carry different AVCS maps to.

[Uncle Scotty]

Originally Posted by west_minist

The question is in high rpm, you may have the precious fuel mixture being blow out @ high avcs. But is this good for the Antilag effect ?

I am assuming and think it is better to have it not advance in high rpm, since the boost is on.

I notice that the 2500-3000 range is a very critical range, even in non AVCS cars, seems to have a note of labouring.

I am assuming that in this area, AVCS could be less (I want to say more), but thats my thoughts.

I will have to see if I can get the STI I am tuning to play with different maps in that area. We have seen gains with different avcs setting in the high load maps, but nothing to really tune in certain areas, since all are road dynos and makes it very diffucult to see.

Also, please note all of this on a Stock OEM computer.

The JDM WRX AVCS map is different to the JDM STI map. Why? I am not sure.

The S20x (eg S202) and STI seems to carry different AVCS maps to.

...yeah.....all the JDM stuff has better ECU tuning....and the EVCS is one of the ways they OBVIOUSLY let the rest of us down

[bboy]

I can't help but ramble....too many variables.

I can believe that the JDM stuff is more aggressive, but I wonder if there is much difference in the shape of the map---sort of a amplitude difference even though the frequency is unchanged.

Scotty...4 or 5 degrees is a lot!!!

The "spool up" region, for lack of a better word, is the region of most interest of me. What I've found is that more AVCS advance just above atmospheric pressure, around 2800-3500 seems to help get the turbo going. Below atmospheric (vacuum) it's very hard to tell. At first I added advance to these load sites (2500-3000, 85-10 mm Hg) and it seemed more slugglish, but the fueling was off, too rich. Now that I lowered the AFR it seems about the same as it was before.

There are a ton of variables: cam advance, spark advance, fueling, plus everything is changing so quickly in those load sites on the road it's hard to know what is "best".

Dyno time is expensive so people don't tune this stuff very often. It would be nice to have a vendor, preferably one that has a load varying dyno, look into general principles. Even then, I know each car will be different. Torque though would seem to be the baseline measurement to optimize. If torque is optimized, then so should the exhaust volume and heat.

Intuatively my larger turbo should have a different AVCS map than the stock turbo, but that may not be true. If one were to look at RPM vs MAP maybe it would be exactly the same for a given set of cams.

I think what I'm going to try a few different maps in the "spool up" region with the fueling adjusted, then switch between them and log the output.

At high boost (let's say 15-20 psi), mid RPM, Phil's map is just about maximized (as much advance as you can run without "flutter"), and that is what I've tried to maintain. After about 4800, AVCS is tapered down and off by around 6000. I'm willing to throw out a little fuel (west-minist) at mid-RPM to get quicker spool or less lag (if that is occuring....anybody know when injectors begin fueling?....it may be after the AVCS-advanced intake valve opening).

[Drac9]

If I get some time in the next couple of weeks I'll throw a car up on the dyno and play with it. I just have been too busy to play around between tuning customer cars and building engines, etc.

[kpowell12]

Good stuff. Once i get time on the dyno again i will talk this over with my tuner and see what we can do.

Also, if AVCS is not activate, what happens? Does it retard or just go to zero during WOT?

-keith

[Uncle Scotty]

Originally Posted by bboy

..................
Scotty...4 or 5 degrees is a lot!!!

The "spool up" region, for lack of a better word, is the region of most interest of me. What I've found is that more AVCS advance just above atmospheric pressure, around 2800-3500 seems to help get the turbo going. Below atmospheric (vacuum) it's very hard to tell. At first I added advance to these load sites (2500-3000, 85-10 mm Hg) and it seemed more slugglish, but the fueling was off, too rich. Now that I lowered the AFR it seems about the same as it was before.
............

yeah....I know.....but I have had access to some data from several JDM ECU's and compared their tables and came up with mine....it isn't perfect, and it hasn't been dyno'd.....but my car, with the stock turbo and a TBE+STi tmic at ~17psi stays right with a full blown FMIC'd, vf39'd, stage4 ecutek'd '04........

[west_minist]

Open it too much in the spool range and you might have too much cooling resulting in lost of power. How much is always the question.

[bboy]

If AVCS is off, the cams are at a normal state of fully retarded. AVCS only advances the intake cam by up to 20 degrees, there is is no retarding of the intake cam from the 0 position.

Oil pressure plays a considerable role in the AVCS actuation. There are some things that are unclear to me. For instance, if the oil pressure is low, is the AVCS slower to respond? It's a closed loop system so oil will flow until the target advance is reached and then hone it on that.

When you say "cooling" west-minist do you mean cooling of the combustion chamber? Cool air would seem good!!

Good reading on cam overlap, scavenging, etc on an NA engine:
http://www.iskycams.com/degreeing.php

Specifically advancing the intake cam's opening and reversion on a NA motor:
http://www.iskycams.com/techtips.php#2002

Ultimately we'll need experience and data, but a little theory from the old ones is not a bad thing. Note: boost changes the equation considerably.

[west_minist]

Yep. I have AVCS on my NA and I cannot tune it. Damn.

Yeah. Advance too much and boosted air just gets push right out

Many thanks for the links

[bboy]

It's true with overlap and boost you can flush the boost out of the exhaust. At mid RPM and high compressor efficiency I think there is some boost to waste on this.

I'm still wondering when the fueling (injector opening) begins relative to intake cam opening. I'm pretty sure the fuel is not pooled behind the valve before it opens. I need to check with someone on when the injector is open, it's going to be on the downward induction stroke.

[kpowell12]

Originally Posted by bboy

If AVCS is off, the cams are at a normal state of fully retarded. AVCS only advances the intake cam by up to 20 degrees, there is is no retarding of the intake cam from the 0 position.

So your saying it should have no effect on peak horsepower numbers on a dyno? It would only directly affect spool up?

[west_minist]

That should be easy to some point. Cam position sensor triggers and injector stuff

[bboy]

It may increase peak torque, but not likely peak power. AVCS is tapering off or off when peak power is reached. AVCS certainly broadens the torque curve.

[west_minist]

Its was really design for torque.

Once I can get my hands on the jdm wrx I am tuning here, I will let you know.

Now let me read those links you sent me.

[Drac9]

If i get a chance i might play with one and do it the same way i do the hondata k-pro stuff. On those what we do is set the cam advance to 0 and tune the car, then we lock the cam at 10 and yune the car, 20, 30, 40, 50 degrees. I make recordings of which dyno pull is the best as I tune each angle then I overlay the top 6 pulls over each other and record where the power is highest- so from 3k-5k it might be 30 degrees, but from 5k-7k it might be 10 degrees. Using this info I build a new i-vtec map based on the best pulls. Then I fine tune that map. With the kpro you have to tune 24 maps to make acomlete tune- high and low cam maps for each 10 degrees of cam advance. It's time consuming but it seems ti work really well. But adjusting the i-vtec map on a turbo rsx I did I gained 80whp.

[west_minist]

I agree w/ that. The only problem is dyno time and access.

[bboy]

I read extensively about other systems of variable cam timing last night. There is not very much information on the tuning of such systems, particularly with a turbocharger.

There are some SAE papers that are written to optimize cam timing around NOx and fuel economy, but not around torque or spooling the turbo.

From our friends in the Toyota, Honda, Mazda, and Mitsubishi communities it looks like the intake cam is advanced beginning around 3000 RPM and continues up to around 6000 RPM in the vacuum regions of the their VVT maps. The tuning of these regions was determined empirically on a dyno and no amount of uninformed futzing was going to see much of a gain. There is a theoretical discussion of timing of the cam to match the resonance of sound pressue waves on a Mazda page, but that would seem to have more to do with their variable intake path than with actual cam timing given a set intake path as in the Subaru.

Advancing the intake cam in the early boost areas seemed to be the more prevalent mode for turbo applications, and in this case the more advance possible without a loss of power/torque the better. All the Subaru and Mitsubishi maps I've seen would seem to bear this out. None the less some information on the torque produced in said regions would seem to be the ultimate guide to tuning of the intake cam advance.

Here is some good data and a half decent discussion from a Mazda page:
http://www.mazda6tech.com/index.php?...id=14&Itemid=1

I also looked into when in the 4 stroke process the injectors begin to fire. This would get at the question of whether or not fuel is being blown out of the induction charge and into the exhaust. I could not find any specific information on our motors, but in general the injectors do seem to begin firing BTDC such that fuel will be pooling behind the intake valve prior to it's opening. There is a great deal of gas velocity/inertia physics in here that would determine if any fuel is escaping out the exhaust valves. I'll have to talk with some other more technical folks about our motors and how much of an issue this may or may not be for AVCS intake cam tuning.

For now, everything points to the need for dyno to determine an AVCS map accurately. The the impediment of exhaust flow through a larger turbo or through a more convoluted header path probably affects the map somewhat, but the intake manifold and cams would seem to have a larger effect. I think if I were to try and optimize tuning of AVCS it would be around MAP vs RPM vs Torque just like any other fuel or ignition timing tuning that I might do.

[bboy]

I've been informed that maybe it's 15 total degrees that AVCS can advance and not 20. I'm pretty sure we talking crank degrees, not cam degrees.

[Element Tuning]

15 degrees of advance at the cam and 30 degrees at the crank.

Thanks,
Phil
www.elementtuning.com

[AZScoobie]

The US STI maxes out at 30 degrees of Advance. There are stops in the Cam wheels. The JDM V8's can run 40 degrees. I have spent extensive time mapping AVCS. On a Big turbo car i can produce 20-40 ft lbs of trq extra and my latest US STI Cam map is producing leading numbers. STI Owners with this map have been very happy with the top end power gains. On a Stock turbo STI the power normaly fades out past 6000 rpm. Most short shift because of this. With my latest cam map power is greater at 7000 then 6000. It really extends the power band.

Clark

[Drac9]

Originally Posted by west_minist

I agree w/ that. The only problem is dyno time and access.

Yup- Luckily I own a dyno dynamics AWD- so no problems there- it's just finding the time to play with it.

[happasaiyan]

Originally Posted by AZScoobie

The US STI maxes out at 30 degrees of Advance. There are stops in the Cam wheels. The JDM V8's can run 40 degrees. I have spent extensive time mapping AVCS. On a Big turbo car i can produce 20-40 ft lbs of trq extra and my latest US STI Cam map is producing leading numbers. STI Owners with this map have been very happy with the top end power gains. On a Stock turbo STI the power normaly fades out past 6000 rpm. Most short shift because of this. With my latest cam map power is greater at 7000 then 6000. It really extends the power band.

Clark

what kind of cam advance are you running in the 6-7k region on that map?