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LGT AVCS Tuning Discussion


Infamous1
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Take a regular screenshot(with the button on your keyboard) then open up MS paint, ctrl V, and select the table and ctrl c, then, ctrl v into a new MS paint document. Sounds like a PITA, but its really easy

 

Thank you. Worked perfectly... except it produces .bmp files, and the forum document importer deems those invalid. Good thing for my editor, although that Paint thing is a good first step.

 

Here is the table. For purely subjective reasons, this works great for me and I've gone back and forth a couple times. It allows great clutch modulation, for example, something of an issue with me and this car until now. But the comparatively low knock sums in both cyl#2 and #4 are especially interesting. FWIW, my IATs have been 100+ lately (and going up! tomorrow).

 

I'm aware that fuel and timing are both affected by changes in AVCS, and that no true comparison can be accurate until they are addressed. However, when it feels so right then to me it has no where to go but up. Like I said, experimenting with AVCS, within reason, is safe, fun, and easy. Do it until you like it... as opposed to leaning it out or advancing the timing until it feels good. Not.

 

I still intend to try fahr_side's table, too. First thing I'll check is knock sum :).

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That is for a wrx, anyone put it on a lgt?

 

This is something that has bugged me for a long time. As far as I know, there is no real difference between the two with the exception of the turbo. Otherwise the same. Certainly nothing different that suggests to me any radical differences in AVCS tuning.

 

So. Tell me. What are the differences, motor wise, that makes people view the two as somehow separate and incomparable. Under my hood I have a comfortable familiarity, burnished after years there with my LGT. Tell me what I'm missing.

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I see you run 30 degrees below 1.00 load between 1600-2400 rpm.

 

I have never tried that.

 

I am curious what led you to try it, any logic behind it, and what benefits did you notice?

 

 

 

I knew you would be back tuning again.;)

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I see you run 30 degrees below 1.00 load between 1600-2400 rpm.

 

I have never tried that.

 

I am curious what led you to try it, any logic behind it, and what benefits did you notice?

 

 

 

I knew you would be back tuning again.;)

 

Hi Ben :D You know how it is.

 

The map there is basically what came on the car, modified somewhat by input from the great NASIOC AVCS thread, and influenced by the "Tuned by STI" 07 WRX's table. As I've said, up until lately I've been taking my time with other tables, AVCS has come last. Other than the jump from stg1 to stg2, no other tuning change has been as noticeable from the driver's seat.

 

Knock sums are very low, compared to pre-AVCS changes, and balanced now unlike before when #4 was at least double #2. After a twenty five mile ride in urban traffic today #2 knock sum was 38 and #4 36. Previous normal counts would be 200+ #4 and 100+ #2. You could watch it increment as you drove along normally.

 

Add that to the ability to let the clutch out smoothly and I'm happy. No more slipping, blipping, lurching. I thought it was me, or the clutch, that made driving the car smoothly almost impossible. But it wasn't, it was the tune... the AVCS tune.

 

In "spirited" driving I don't really notice anything. It still rips, accelerating faster than I'm able to analyze. Nothing stands out as having changed, and understandably so since as mentioned at WOT the car is basically using the last load column, all the fancy cell work ignored. All the rest is for driveability... and for Subaru, of course, emissions. I'm not as green now, but I'm much happier with my car, and I was really happy before. :)

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Its funny that knock sum has come up, I was looking at that specifically on a stock LGT, and I couldn't believe how high it was! It rest at least 3 times on a relatvely short run, but with mine the way it is, was still on its first set(like in the 20's)
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This is my current table. I see no improvements running more than 30* at any rpm/load site. I see only less torque if I run over 0* past 5,200rpm. Running more than 10* before 0.80 load does me no favors for torque.. fuel economy is increased but so is vibration and bucking / hesitation.

 

I thought it would make good sense for the cruising areas (2200-3000 and .3 to .8 or so load) to all be around 10* to keep the avcs from having to do a whole lot in the normal driving ranges. This mostly worked out well, but I noticed a lack of smooth acceleration starting around .7 load at 2600 or so rpm and going to 1.3 or so at 2800 only in 6th gear. Mainly moving from 65-75 on the highway.

 

I started ramping up AVCS a bit earlier as you can see in my previous screenshot and it seemed to help though I was still getting some of that mild stumbling/bucking. I believe it is more of a timing issue, as my timing really starts to drop off at 2800 and 1.1 load due to tons of knock sum incrementing there. I'm not sure if I should let it or not but removing timing seems to reduce the knock though I believe it begins to effect drivability. I'm not sure if trying to make up for it with AVCS tuning is right or not.

 

This makes me wonder if I should go back to using the cruise/non cruise timing logic and also makes me wonder if you are using curise/non cruise logic for your timing and/or AVCS tables. If so, how does your cruise AVCS table differ?

 

At this point I've gone back to mostly 10* in the cruise region and have tweaked the CL Fuel Target comps A/B to run a bit richer than 14.7 in the whole cruise region, and going richer at 1.1 load than what I see most people running. I'm at about 14.2 in the whole cruise region, down to 13.8 at 1.3 load and this seems to have made the most difference in smoothing out the cruise region (other than removing the 30-40* areas of AVCS in the cruise range) though there is still some barely noticeable stumble at times.

Edited by rtbrjason
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I thought it would make good sense for the cruising areas (2200-3000 and .3 to .8 or so load) to all be around 10* to keep the avcs from having to do a whole lot in the normal driving ranges. This mostly worked out well, but I noticed a lack of smooth acceleration starting around .7 load at 2600 or so rpm and going to 1.3 or so at 2800 only in 6th gear. Mainly moving from 65-75 on the highway.

 

I started ramping up AVCS a bit earlier as you can see in my previous screenshot and it seemed to help though I was still getting some of that mild stumbling/bucking. I believe it is more of a timing issue, as my timing really starts to drop off at 2800 and 1.1 load due to tons of knock sum incrementing there. I'm not sure if I should let it or not but removing timing seems to reduce the knock though I believe it begins to effect drivability. I'm not sure if trying to make up for it with AVCS tuning is right or not.

 

This makes me wonder if I should go back to using the cruise/non cruise timing logic and also makes me wonder if you are using curise/non cruise logic for your timing and/or AVCS tables. If so, how does your cruise AVCS table differ?

 

At this point I've gone back to mostly 10* in the cruise region and have tweaked the CL Fuel Target comps A/B to run a bit richer than 14.7 in the whole cruise region, and going richer at 1.1 load than what I see most people running. I'm at about 14.2 in the whole cruise region, down to 13.8 at 1.3 load and this seems to have made the most difference in smoothing out the cruise region (other than removing the 30-40* areas of AVCS in the cruise range) though there is still some barely noticeable stumble at times.

I started out by using the same map for cruise and non-cruise but found the same roughness you did. After a while I tried a less aggressive non-cruise map and that helped. I honestly don't know what conditions trigger the shift between cruise and non-cruise maps so I don't like to use them for timing. I think it's better to have slightly wrong ignition timing than to have sudden shifts up and down as maps are swapped. Since I don't fully understand this switch I am reluctant to play with it too much. For this same reason I tried to make the values in the AVCS maps similar where the changeover seems to occur, in order to smooth it out.

 

My cruise AVCS table attached. This is developed out of a Stage 1 map from Eric Minehart, though I increased cam advance in the range of 0.80 to 1.40g/rev, ramp back to zero much earlier, and of course it's rescaled. Improving VE doesn't always get more torque, if you have to reduce timing to compensate. It's very easy to get into a tail-chasing situation when three variables affect each other this closely... VE, boost and ignition timing. I just feel that more VE and less timing in this 1.00g/rev +/- transition area gives decent torque while being reasonably smooth, and not sacrificing much in spool. I don't believe there is a perfect map... it's all down to what you are looking for.

avcs_cruise.png.30910e404d00268597547b4aa30faf0a.png

Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs.
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Hey you guys seem to know this stuff. Quick run down. Im at stage two and have been for awhile. Never had any problems, was tuned by infamous. Out of nowhere now Im getting a CEL of Cam Overtiming. Do any of you have any ideas y or what to do. Thanx in advance?
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Its funny that knock sum has come up, I was looking at that specifically on a stock LGT, and I couldn't believe how high it was! It rest at least 3 times on a relatvely short run, but with mine the way it is, was still on its first set(like in the 20's)

 

knock sum will fluctuate a lot especially after an ecu reset, what is noteworthy is the FLKC and the FBKC. Knock sum can fluctuate but the FLKC and FBKC still be zero (normal)

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Hey you guys seem to know this stuff. Quick run down. Im at stage two and have been for awhile. Never had any problems, was tuned by infamous. Out of nowhere now Im getting a CEL of Cam Overtiming. Do any of you have any ideas y or what to do. Thanx in advance?

 

 

cam timing over advance will pop up with a CEL when the heads are starved of oil. This can happen if the AVCS lines get clogged and no oil enters the head at the top.

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knock sum will fluctuate a lot especially after an ecu reset, what is noteworthy is the FLKC and the FBKC. Knock sum can fluctuate but the FLKC and FBKC still be zero (normal)

that was the funny thing, He had the factory tune, never reflashed it, He had an exhaust leak that he thought sounded like a boost leak(hogzawsted, 3 washers) It ended upbeing just air hitting the bumper

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  • 2 weeks later...
Wanted to share what I ended up with after playing around with AVCS most of the weekend. This was really the last piece for me and having tried many different types of AVCS mappings with a variety of timing strategies, the attached image is what works best on my car. The WOT region isn't largely different than what most others are running. The cruise region is tuned to run as smooth as possible as this is where I spend most of my drive time. The adding of some advance at 2400rpm over the rest of the cruise region seemed to solve the low rpm acceleration stumble I was getting.

348195358_finalavcs.thumb.jpg.dc9085336569f01498707ea08e424882.jpg

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  • 2 years later...

Bumping an old thread here...

 

I was looking at my AccessPort readout for "AVCS in" on both the L & R sides. It seems like my left side is responding a fraction of a second more slowly. The values are almost always identical, but the left side gets there a fraction of a second later. Sometimes the left side will have a slightly higher peak value (ex: 46 vs 45).

 

Do I need to replace my OCVs? Or is this variance normal?

LW's spec. B / YT / IG
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Awesome thread! I'm about to start playing with the AVCS map myself. Do we know what the valve overlap is at 0* advance? Thing to watch out for here is reversion, especially with non equal length headers and stock turbos.

 

In Nissan SR20 world we turbo stock motors with great results, but that's because Nissan built the SR20DE's to be turbo motors. SR20DE stock cams generally have under 10* of overlap, thus reversion is kept to a minimum. I once built a turbo SR20VE (like v-tech, not oem turbo) with a log manifold and a big T3 turbo. Low lobes had 0* of overlap thus it made good power until I would switch to high lobes which had 48* of overlap. I would actually loose power and have detonation when switching to the high lobes due to reversion. When Nissan decided to OEM boost the SR20VE motor, they made new cams for it, low lobes at 0*, and high lobes at 13* of overlap. After I installed these cams into my motor, the car stopped knocking as much and gained more power.

 

Moral of the story, if your going to have a bad flowing manifold with cylinders that contaminate each other, too much overlap will hurt your power. The more boost you run the more back pressure you have, which leads to reversion and powerloss. This is why you guys saw knock count reduction after removing the emission spikes.

 

Now you might ask, why bother with having any overlap at all then. Scavenging, which only really benefits NA motors but can benefit big turbo motors.

Edited by covertrussian

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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  • 4 years later...
Awesome thread! I'm about to start playing with the AVCS map myself. Do we know what the valve overlap is at 0* advance? Thing to watch out for here is reversion, especially with non equal length headers and stock turbos.

 

As best I can tell, the overlap at 0.006" ranges from 0 (with 0 AVCS advance) to 40 degrees (with 40 degrees AVCS).

 

At 0.050" it ranges from -34 degrees (no advance) to +6 degrees (40 degrees advance). And the intake valve closing angle ranges from 47 to 7 degrees after BDC.

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Been a long time since I looked at this thread, since then I've switched turbos (VF46 to EVO 3 16G w/8cm^2 housing), tried a couple different headers (Tomei ELH and GS Ported UEL). Tested my manifold backpressure (19.75psi of pre-turbo back pressure at about 12psi manifold pressure with Tomei ELH).

 

In the end I found my car absolutely hates any AVCS above 3k RPM, especially on Stock style UEL headers, it becomes very knock prone and requires a lot of timing to be pulled, without any power gains. This is my current GS Ported UEL header AVCS map that reflects that:

attachment.php?attachmentid=270537&stc=1&d=1541694307

 

 

What about equal length headers? While they were less knock prone (read: allowed me to run more timing then even MBT), more AVCS did increase the MAF voltage, back to back road pulls showed no power increase, even after fine tuning the timing. Thus my optimal AVCS map was fairly close to the GS UEL one above.

 

 

 

As best I can tell, the overlap at 0.006" ranges from 0 (with 0 AVCS advance) to 40 degrees (with 40 degrees AVCS).

 

At 0.050" it ranges from -34 degrees (no advance) to +6 degrees (40 degrees advance). And the intake valve closing angle ranges from 47 to 7 degrees after BDC.

 

I actually mapped these out in this thread: AVCS Timing And Overlap (2005-06 vs 2007-09)

 

I found that 2005/06 FSM has a typo for exhaust camp durations, thus 2007+ FSM seems to be more accurate, which gives us this:

attachment.php?attachmentid=239738&stc=1&d=1477486376

 

Based on this we can see that 0* AVCS is 0* overlap, but you are right it will vary at different lifts.

attachment.php?attachmentid=239744&stc=1&d=1477488132

126630323_CRAVCS10-5Map.PNG.2d29a7735239361f47d25ce1557b51a4.PNG

Edited by covertrussian

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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