Welcome to the North American Subaru Impreza Owners Club Monday March 18, 2019
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC Technical > Engine Management & Tuning

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 10-05-2018, 12:46 PM   #801
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Quote:
Originally Posted by NSFW View Post
What do you think the factory ECU uses?

Has anyone actually measured the mechanism with a protractor? What did you / they find?

I have a partially disassembled exhaust AVCS mechanism, but no protractor.

If I understand how the AVCS solenoid and mechanism work, oil pressure fluctuations wouldn't matter much unless it drops WAY down. If oil pressure goes up or down (and the solenoid doesn't vary the split) the oil pressure goes up or down the same amount on both sides of the lobes, so there shouldn't be much movement. Unless the oil pressure drops so low that it can't overcome the return spring on the exhaust side or the... opposition (for lack of a better word) from the valvetrain on the intake side.

My LGT runs 30 degrees of intake advance in cruise, with BC 272 cams, and it's very stable. Unless you really want max advance/retard below 1500 RPM I'd be surprised if you had trouble getting it. And if you do want max at such low RPM, I gotta ask, why?
Since you have one in-hand - post your picture of the mechanism with the inner lobes installed and pressed against one stop (take a straight-on view photo for me).

I have measured this before in the past, and I believe this thread actually has the info... but I'm just too busy to dig at the moment.

Oil pressure fluctuations DO matter, and oil temperature matters even more. Achieving 45 deg advance at idle, for example... well you can get 50 easily, because that slams up against the physical stop. Anything about about 30 deg @ idle or a little above and you'll have a decent amount of jitter. As this affects VE strongly, this is a very bad thing for stability. Using my 2006 EJ257 motor as an example as I've logged more data on that than anything else - the 35-49 degree range is the no-go zone.

You hit the nail on the head though - 30 degrees at cruise is fine. It's the 35-49 degree range you'll likely have issues with. Again, 50 is easy - the way the PWM works on these is by having a center value that holds advance at a stable position. Move the PWM % up 1 point and the advance will climb slowly, 2 points and it will climb extremely fast, and 3 points and you'll slam into a stop. I've had to program the control from scratch for my MoTeC M800 and it was eye-opening to realize the PWM control range used is like 7% out of the full 100% range.

EDIT: Read my comments here - https://forums.nasioc.com/forums/sho....php?t=2809286

These were posted closer to when I was performing the PWM programming of my motor and now I remember what it was! The EJ207 motors have a center PWM value that targets about 25 degrees advance allowing for full tuning within the 0-50 degree advance range (the factory used 0-45 deg on single AVCS EJ207 motors). The 04-06 EJ257 motors had a center PWM value that targets about 10-15 degrees advance. What happens with this, is that the 0-30 (maybe 35) degree range is stable, but the 35-49 degree range is unstable due to the necessary PWM values to achieve this advance being too far from the center value (causing hunting).

EDIT 2: Took a look at an older AVCS mechanism picture I found online - cam advance max = 25 degrees equating to 50 degrees @ crank. The 'tooth' with the 2 side bumps at the bottom is the physical stop 'tooth'. If I had to guess, those raised stops are probably manufactured long and machined to accurate size during the manufacturing process. Factory ECU tables are in crank degrees.

* Registered users of the site do not see these ads.

Last edited by mrsaturn7085; 10-05-2018 at 01:10 PM.
mrsaturn7085 is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 10-05-2018, 09:30 PM   #802
NSFW
Scooby Guru
 
Member#: 140444
Join Date: Feb 2007
Chapter/Region: NWIC
Location: Near Seattle, WA
Vehicle:
05 Stage Free LGT
ATP 3076, 6MT, AVO FMIC

Default

As far as I can tell, the "center" PWM value doesn't target any particular amount of advance, but rather it targets zero change of advance. Small deviations from that center will cause the amount of advance to increase or decrease, and the ECU returns to the "center" value when the desired advance is achieved. (Or desired retard, for the exhaust cams.)

I will confess to not logging it enough to be absolutely certain of that, but I made a standalone exhaust AVCS controller for my single-AVCS car based on that assumption, and it works. I got the idea from looking at an exhaust AVCS log from an 08 STI. The "center" values moves around over time but it doesn't seem to correlate with anything obvious like RPM.

The factory tune for my wife's 2009 LGT has an island of 40 degrees of intake advance.

The exhaust AVCS pulley that I mentioned is a paperweight on my desk at work, but I'll get a picture of it on Monday.
NSFW is offline   Reply With Quote
Old 11-19-2018, 01:24 AM   #803
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

so im about half way through reading this whole thread so im not sure if this has been talked about a whole lot...

im trying to get my AVCS dialed on my ej205. im running it on speed density... so, my plan to tune the WOT part of my map is to tune my VE to a flat AFR of 11:1 on my current map which runs fairly well (has some advance then tapers to 0) then advance my AVCS a few degrees and log my AFR and and keep parts of the map that make it run leaner. repeat until i run out of AVCS or it starts going richer again (tuning each cell to leanest AFR) or in other words tune AVCS to give me the highest values in my VE table to maintain AFR. then adjust my OL fuel/ignition to finalize the power portion of the tune. does this sound reasonable?

for highway cruise region i think i should adjust my timing and AVCS to get lowest possible injector cycle indicating most efficiency. reasonable approach?
once i tune those arias there is not a whole lot left of a MAP based AVCS table so it would then be up to smoothing and adjusting for torque and smooth drive?

it seems like SD might be easier since i dont have to fart around with g/rev and MAFv just look at when things lean out...
or am i totally off on my approach to this?
CarmelValleyWRX is offline   Reply With Quote
Old 11-19-2018, 01:22 PM   #804
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Quote:
Originally Posted by NSFW View Post
As far as I can tell, the "center" PWM value doesn't target any particular amount of advance, but rather it targets zero change of advance. Small deviations from that center will cause the amount of advance to increase or decrease, and the ECU returns to the "center" value when the desired advance is achieved. (Or desired retard, for the exhaust cams.)

I will confess to not logging it enough to be absolutely certain of that, but I made a standalone exhaust AVCS controller for my single-AVCS car based on that assumption, and it works. I got the idea from looking at an exhaust AVCS log from an 08 STI. The "center" values moves around over time but it doesn't seem to correlate with anything obvious like RPM.

The factory tune for my wife's 2009 LGT has an island of 40 degrees of intake advance.

The exhaust AVCS pulley that I mentioned is a paperweight on my desk at work, but I'll get a picture of it on Monday.
I missed this reply but you are almost entirely correct. The center value targets zero change of advance AND a return to a zero position on the cam. I've had to log this to tune cam control on a MoTeC system and confirm this is how it works.

If you set duty for 100% then return to the center PWM value, you will see a slow creep from max advance back to the center advance value (i.e. zero position). On the 04-06 EJ257, this zero position is below the half-way point of the advance range. On the pre-2008 EJ207, this is almost right @ 25 deg (the halfway point).

To reduce advance, the ECU doesn't just return to the center value because that would pull the advance back down very slowly. It will undershoot, going below center PWM value, respecting PID parameters within the ECU itself. Boost control and cam control are very similar in the Subaru ECU.

Quote:
Originally Posted by CarmelValleyWRX View Post
im trying to get my AVCS dialed on my ej205 ... does this sound reasonable?

for highway cruise region i think i should adjust my timing and AVCS to get lowest possible injector cycle indicating most efficiency. reasonable approach?
once i tune those arias there is not a whole lot left of a MAP based AVCS table so it would then be up to smoothing and adjusting for torque and smooth drive?
I'm going to jump around a bit here:

You're definitely highlighting why OEMs use an engine dyno and hundreds (or thousands) of tuning hours in the development of an OEM map. If you were just tuning fuel and spark, it's pretty easy to make changes and see results. Add cam control into the mix and you've changed the entire VE of the motor itself in the affected area of the AVCS map. Throw a second adjustable cam into the mix and you've compounded your options yet again. Then on top of all that, you have injection timing.

Every tuner will have their own system, but first and foremost, you need to do a few things:

1. Have your injector data locked-in, accurate, and do not change it.
2. Have your speed density compensations set reasonably well.
3. Set a best-guess AVCS table and DON'T change it until you have a well dialed-in tune.

Change any of those three things, or any mechanical aspects of the motor in a speed density tune, and you might as well start with a base map again. Once you have this tune pretty well refined, you can then play with certain elements (compensations or cam advance - don't touch the injectors... period) and see how the engine responds on the dyno (or as logged data). Changing AVCS 'islands' at this point is reasonable, but you need to remember that fuel/timing (and maybe injector timing) will need to be optimized again.

E-tuners and one-and-done tuners tend to just keep a few variables in mind (which is why a 'protune' is just a base map and an e-tune is almost always a waste of money). When you move into this level of tune refinement, you need to consider quite a bit more. For example - lean cruise:

1. Do emissions matter to you? No? Good, that eliminates a large variable.
2. Injector duty is a good measure of fuel consumption, but...
3. ...go too lean and you could have detonation (uncommon at low load)...
4. ...or cylinder heating could also become an issue leading BACK to #3 or pre-ignition due to hot spots.

Many professional and well respected aftermarket tuners know very little about efficiency tuning and zero about emissions tuning. Keep that in mind - YOU will probably be the expert for your own car in this regard, should you decide to pursue this goal on your tune.

Injection timing (if you can alter it) makes a HUGE difference on boxer motors for fuel consumption, primarily at idle.

Tuning to a flat AFR rather than dyno tuning to torque output is not a great idea - it's a shortcut and much less than optimal.

Last edited by mrsaturn7085; 11-19-2018 at 01:44 PM.
mrsaturn7085 is offline   Reply With Quote
Old 11-19-2018, 02:29 PM   #805
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

ok... sounds like its down to experimentation on the side of cruise and light throttle.

but you are saying maximum VE is not what we want at WOT? luckily i only have intake AVCS bit its still a PITA. i can adjust injector timing but was planing on messing with it once i get a nice AVCS map in there. it seems like the AVCS is the keystone map of the whole tune and everything revolves around it.
i guess for now i will just base my injector map on my AVCS advance. right now its running the group-n injector time event though i have changed the AVCS. i wonder what issues its causing me...?

i have noticed alot of tuners and enthusiasts focus on the WOT which is only one column of each map. hardly a full tune. i spent countless hours dicking around with idle/vacuum arias and my car now pulls pretty hard before even making 2psi of boost. i have never had good luck tuning my maps for "spool". i have gotten 20psi by 2500rpm but my car did not move so i though that wasnt a good idea

Last edited by CarmelValleyWRX; 11-19-2018 at 02:49 PM.
CarmelValleyWRX is offline   Reply With Quote
Old 11-19-2018, 05:41 PM   #806
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Quote:
Originally Posted by CarmelValleyWRX View Post
ok... sounds like its down to experimentation on the side of cruise and light throttle.

but you are saying maximum VE is not what we want at WOT? luckily i only have intake AVCS bit its still a PITA. i can adjust injector timing but was planing on messing with it once i get a nice AVCS map in there. it seems like the AVCS is the keystone map of the whole tune and everything revolves around it.
i guess for now i will just base my injector map on my AVCS advance. right now its running the group-n injector time event though i have changed the AVCS. i wonder what issues its causing me...?

i have noticed alot of tuners and enthusiasts focus on the WOT which is only one column of each map. hardly a full tune. i spent countless hours dicking around with idle/vacuum arias and my car now pulls pretty hard before even making 2psi of boost. i have never had good luck tuning my maps for "spool". i have gotten 20psi by 2500rpm but my car did not move so i though that wasnt a good idea
VE at a given load cell (usually RPM vs. MAP on speed density) changes with cam advance. The primary two open loop tables using these load cells are fuel and spark. Let's say you limit cam advance to a discrete 0, 5, 10, and 15 degrees - you might as well be tuning 4 motors now as you've got a fuel and spark table that is 100% unique for ALL 4 cam advance values (8 total tables).

Now lets say you also have exhaust cams and you have 4 discrete values - 0, 5, 10, and 15 degrees. You've now got 16 motors worth of tuning (32 tables, only considering fuel and spark).

NOTE: some OEMs actually DO tune this way... and the ECU literally has fuel/timing maps for a handful of discrete cam advance values - this is called 4D tuning (the fuel and timing tables reference 3 variables for lookup, rather than 2). Subaru has chosen another method - there is only one or two valid AVCS tables in these ECUs and then there are only a few spark/fuel tables to go along with it. This is 3D table tuning (with table switching, in some cases). Adding table switching (cold vs. warm motor, cruise vs. normal driving, etc.) does not make this into true 4D tuning, in my opinion.

This is why the AVCS table is a cornerstone for tuning that should not be messed with before the implications of changing things are realized - it affects the VE across the entire fuel/spark tables (among others).

WOT throttle tuning is good for establishing safe limits on a tune, but it really only gives you a base map. A better base map uses WOT throttle tuning with clamped throttle stripes:

cruise (you probably will not be able to reach redline until 10-15% throttle):
5% throttle at 100% pedal
8% throttle at 100% pedal
10% throttle at 100% pedal
15% throttle at 100% pedal

transitional:
20% throttle at 100% pedal
30% throttle at 100% pedal
40% throttle at 100% pedal
60% throttle at 100% pedal

wide open:
80% throttle at 100% pedal
100% throttle at 100% pedal

Filling in these stripes then interpolating will give you a solid base map in a very efficient way. By starting with wastegate spring pressure and raising boost (tuning boost control) along each throttle stripe, you can fill in an absurd number of load cell data in a short amount of time.

And yes, you want maximum VE under WOT.

Subaru motors unfortunately need quite a bit of added fuel for cooling under load so it's not quite as easy as just looking for lean/mean best torque w/o knock and then calling it a day. Tunes like that are the type that perform wonderfully on the dyno or an occasional street pull, but as soon as you put the car on a race track with a sustained load, it melts a cylinder.

Last edited by mrsaturn7085; 11-19-2018 at 05:54 PM.
mrsaturn7085 is offline   Reply With Quote
Old 11-19-2018, 06:17 PM   #807
Hyper
Scooby Guru
 
Member#: 15822
Join Date: Feb 2002
Location: MOCKBA
Vehicle:
1999 WRB GM6
2.34 LR destroker

Default

you want maximum VE everywhere

we should make a thread on injection timing, I've been playing with it, but my brain starts malfunctioning when AVCS comes in play, since you want it dialed in not only at idle but also at cruising for better burning/fuel consumption. basically anywhere under 4000 RPM since anything above that and it already make no difference based on my recordings
Hyper is offline   Reply With Quote
Old 11-19-2018, 07:49 PM   #808
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Quote:
Originally Posted by Hyper View Post
you want maximum VE everywhere

we should make a thread on injection timing, I've been playing with it, but my brain starts malfunctioning when AVCS comes in play, since you want it dialed in not only at idle but also at cruising for better burning/fuel consumption. basically anywhere under 4000 RPM since anything above that and it already make no difference based on my recordings
Good call.

A good read on injection timing with some Subaru specific notes:

https://www.motec.com.au/forum/viewtopic.php?t=769

To summarize:

1. As you adjust injection timing, the ideal value is the value that gives the richest reading.
2. Subaru motor with the TGVs gutted will benefit from injection timing tuning (from 0-3250 RPM on the EJ207 and likely other EJ motors).

MoTeC base maps for Subaru motors only have a non-linear region between 800-3250 RPM and 0-100 kPa (absolute). This would agree with your findings that above cruise RPM (or under boost), it doesn't matter much.


Last edited by mrsaturn7085; 11-19-2018 at 07:55 PM.
mrsaturn7085 is offline   Reply With Quote
Old 11-19-2018, 09:02 PM   #809
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

im still confused... your saying AFR is not a good way to tune but since im using a speed density MAp/rpm table it seems like wideband AFR reading comparing one AVCS setting to the next would be a good way to judge VE.!? i have carberry so that means i have dual maps controlled by a switch. plan is run it with one AVCS setting and VE table, log AFR of WB. then switch maps to a slightly advanced or retarded AVCS setting using the SAME VE table and log WB again. then look at logs and use values that caused leanest AFR to build a new map... retune VE to get back to safe AFR if it leans too much. repeat until i find AVCS that has the highest VE. i would set all of my maps to be the same other than AVCS. only reason i would run 11:1 in my OL table so its easy to see how far off my VE values are using my WB. i would run timing that i feel is safe and listen through det cans. once i find the highest VE at WOT then i would worry about finding optimal fuel/spark setting. it seems like this would work?

BTW i also have an EGT on #4 that streams into RR logger if i could use that to tune in any way? it responds semi fast.

my main issue im having is that my setup is not too common (2.1 stroked JDM forester motor + 9.5:1CR + AVCS + vf48/EWG + speed density)so im having to build all my tables from scratch basically. my ignition is pretty good now and my VE is fairly accurate for my current AVCS settings. but i know my AVCS is not set up right. the "stock" carberry AVCS setting ran horribly and there are not many (any?) people who have made an AVCS map using MAP/rpm table for the engine i have.
once i can settle on an AVCS setting the rest of the tune is rather simple.

Last edited by CarmelValleyWRX; 11-19-2018 at 09:16 PM.
CarmelValleyWRX is offline   Reply With Quote
Old 11-20-2018, 04:33 AM   #810
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

I was referring to injection timing when I said to tune for richest value possible.

Changing cam advance alone is not going to tell you much - the ignition timing (definitely) and target AFR (maybe) will need to be adjusted to determine if the AVCS change was a good or bad one - and it still needs to be done on a dyno to tell you the net torque change. That's the slow part... you have to re-optimize the cell every time VE is modified.
mrsaturn7085 is offline   Reply With Quote
Old 11-20-2018, 05:35 AM   #811
Hyper
Scooby Guru
 
Member#: 15822
Join Date: Feb 2002
Location: MOCKBA
Vehicle:
1999 WRB GM6
2.34 LR destroker

Default

when road tuning the cams, I usually set the table flat with different values, log the runs and then compare VE and use virtual dyno tool
its really a half-ass way of doing it, but is the only tool you have on the road
I wish I had a dyno, I would fine tune the crap out of my motor
Hyper is offline   Reply With Quote
Old 11-20-2018, 12:51 PM   #812
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

i guess i will have to tune for VE at the top end/WOT. i dont think road dyno would be accurate enough (on my roads) to detect small torque change.
yes tuning injectors for rich AFR makes sense. that would give the injector the lowest duty cycle to maintain 14.7 cruising/idling.
CarmelValleyWRX is offline   Reply With Quote
Old 11-20-2018, 06:55 PM   #813
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Doing blanket table changes is a good way to tune the loaded parts of the table... but part throttle and efficiency tuning would be a nightmare without an engine dyno that could do load holding or pattern runs.
mrsaturn7085 is offline   Reply With Quote
Old 11-21-2018, 06:42 PM   #814
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

can anyone tell me if this AVCS looks reasonable/logical or am i way off? im pretty sure i need to tone down the advance though because i can feel the car pull harder once the AVCS turns off. also do you guys think an EWG will make a big difference in the AVCS required since back pressure should be alot less than a regular VF turbo/stock cat back?


Last edited by CarmelValleyWRX; 11-21-2018 at 06:49 PM.
CarmelValleyWRX is offline   Reply With Quote
Old 11-21-2018, 08:54 PM   #815
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Your rollback to 0 advance might be taking place a little early in the RPM band and you take a fairly sudden dive between 4200-4600... I would stretch this out over 800 RPM to go from 17 to 6 to 0 or so.

Your advance near atmospheric might be a little low, too. Usually by 14.7 psia you'll be 20-30 deg advanced already at lower RPM.

Lastly, you'll probably never see these values, but low RPM, high boost usually doesn't drop like that.

Here's STI's in-house GpN map for the single AVCS EJ207:



Won't match yours perfectly, but it's probably a good direction to head from where you're at. Clean up the 5300+ RPM area for sure - the GpN cars all shifted here so they didn't tune AVCS above this point.
mrsaturn7085 is offline   Reply With Quote
Old 11-21-2018, 09:59 PM   #816
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

i mostly smoothed it (lowrpm high load) out for OCD sake. my engine seems to not like much AVCS at low rpm. but i never get past 1 bar until 2000+ rpm. i wish i had measured my cams. i have a feeling the forester ej205 has quite different settings than the ej207 or wrx ej205. it seems to not like lots of advance even though the cams go to 45'.
CarmelValleyWRX is offline   Reply With Quote
Old 11-21-2018, 10:31 PM   #817
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

here is my map. i have not flashed it or tried it... we will see how it reacts to more timing at lower MAPs.

CarmelValleyWRX is offline   Reply With Quote
Old 11-27-2018, 02:55 AM   #818
Pssyboost
Scooby Newbie
 
Member#: 481715
Join Date: Feb 2018
Default

Does AVCS really make that much difference?
I haven't heard many people here talk about tuning it...
Pssyboost is offline   Reply With Quote
Old 11-27-2018, 10:19 AM   #819
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Quote:
Originally Posted by Pssyboost View Post
Does AVCS really make that much difference?
I haven't heard many people here talk about tuning it...
Yes - though it is a difficult tuning topic without a good deal of time (and money, if renting dyno time). Read my posts earlier on this page and you can quickly see why.

If you are ONLY tuning for a race car, AVCS becomes far less important as the main benefit is low-end drivability and fuel economy while still retaining the mid- to high-end power.

I have a theory that dual (intake + exhaust cam) AVCS also has some added utility in twin-scroll applications for maximizing high-end power but the second part of this theory is that no one in the aftermarket (especially in the USA) has really explored this enough to realize these benefits - generally speaking, by the time a builder/tuner is looking for this last bit of power, they've already abandoned small twin-scroll turbos for a large single scroll unit.

The basic idea behind what I'm talking about is that twin-scroll applications reduce manifold back-pressure, you can run more overlap giving approximately 5% better power in the upper range of the RPM band. The limiting factor is whether or not the OEM AVCS system has the advance/retard range to accommodate this.
mrsaturn7085 is offline   Reply With Quote
Old 11-27-2018, 10:40 PM   #820
NSFW
Scooby Guru
 
Member#: 140444
Join Date: Feb 2007
Chapter/Region: NWIC
Location: Near Seattle, WA
Vehicle:
05 Stage Free LGT
ATP 3076, 6MT, AVO FMIC

Default

The other thing about AVCS, and especially dual AVCS, is that it allows running bigger cams without the drawbacks that are typically associated with big cams. I think I said earlier that if I'd known more about cams and AVCS a couple years ago I would have skipped 272s and gone straight to 280s. With dual AVCS and 272s my engine idles and cruises just like stock.

AVCS by default moves the lobe centers away from each other, which reduces overlap, which makes a big cam behave more like a small cam in terms of idle stability and low-RPM drivability. Then you can move the lobes toward each other as much or as little as you want.
NSFW is offline   Reply With Quote
Old 11-28-2018, 01:35 PM   #821
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

NSFW hit the nail on the head for why OEMs tend to use adjustable VE on motors this way. The difficulty usually arises when an individual user wants to try to do the same thing. As I mentioned above, it takes a TON of development time to get to near-OEM levels of refinement on anything beyond a max torque pull.

This stuff was pretty simple stuff back when you had binary low and high cam maps (Honda VTEC), but when variable cam advance came into play, the amount of work involved in fine tuning a motor exponentially increased. Even on VTEC motors, in motorsport, everything is generally distilled down to a simpler system - most early Honda race cars based on production models locked the cams into high lift only whenever the rules allowed for it (and sometimes ran a hollow cam with the low-lift lobes removed entirely).

The biggest opportunity we have as individuals is to cut emissions considerations entirely. When you distill it to only torque output and fuel economy, you've got an easier job (even though it's still a mountain of work).
mrsaturn7085 is offline   Reply With Quote
Old 12-01-2018, 12:30 AM   #822
NSFW
Scooby Guru
 
Member#: 140444
Join Date: Feb 2007
Chapter/Region: NWIC
Location: Near Seattle, WA
Vehicle:
05 Stage Free LGT
ATP 3076, 6MT, AVO FMIC

Default

Quote:
Originally Posted by NSFW View Post
The exhaust AVCS pulley that I mentioned is a paperweight on my desk at work, but I'll get a picture of it on Monday.
I'd almost forgotten, but here it is:

https://imgur.com/a/X2NMUde
NSFW is offline   Reply With Quote
Old 12-02-2018, 04:08 PM   #823
mrsaturn7085
Scooby Specialist
 
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2006 Impreza WRX STI
WR Blue

Default

Looks identical to the one I posted - I'll check the angle this Monday when I've got a real PC to use.
mrsaturn7085 is offline   Reply With Quote
Old 12-09-2018, 06:00 PM   #824
CarmelValleyWRX
Scooby Specialist
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

can someone critique my AVCS timing curve? this is VD power and torque. im wondering if my AVCS bump should move closer to my peak torque bump?





not bad for 2.1l + VF48


hers a graph of my AVCS, MAP, and ignition timing. my timing could use some smoothing.


Last edited by CarmelValleyWRX; 12-09-2018 at 06:05 PM.
CarmelValleyWRX is offline   Reply With Quote
Old 01-07-2019, 04:10 AM   #825
NSFW
Scooby Guru
 
Member#: 140444
Join Date: Feb 2007
Chapter/Region: NWIC
Location: Near Seattle, WA
Vehicle:
05 Stage Free LGT
ATP 3076, 6MT, AVO FMIC

Default

Ran across this and thought it would be of interest to anyone following this thread...



Originally posted here: https://www.lotustalk.com/forums/f17...ontrol-464730/
NSFW is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Let's talk hybrid economy / performance tuning Bad Noodle Open Source Reflashes 17 04-29-2012 09:30 PM
Let's talk flywheels WRXThis Transmission (AT/MT) & Driveline 9 04-17-2002 02:04 PM
Let's talk about when to change out the rods. Andrew Normally Aspirated with bolt-on Forced Induction Powertrain 10 03-04-2002 11:44 AM
Let's talk amps.... Teh Legacy Car Audio, Video & Security 15 10-19-2001 02:09 AM
Let's talk about the Rimmer Supercharger rao General Forum Archive 88 09-21-2000 07:56 AM

All times are GMT -4. The time now is 10:42 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2019 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.