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Old 12-16-2009, 11:55 PM   #251
JSarv
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Ken is going to bust your balls for that.

Dwell will not increase airflow in no way shape or form. Howerver it can and will make the combustion more complete and efficiency will be increased until the limit of the pack is reached. However if the combustion process is very complete to begin with, dwell increase will only be a waste of energy.

There are limits to everything, if you have a 100% combust in cylinder in less than 15* of crank rotation nothing will add more power other than a higher cylinder pressure (boost/cfm) - so if your combustion was already to the point where adding dwell had no benifit to the combustion, well you get the point.

Odds are you ran more boost up top. In an fi car boost/turbo creates given flow - nothing else.

Having a more efficient engine produces more power at the same airflow (given a higher efficiency can be obtained) such as a better spark resulting in a more complete combustion.

Andy - you mean the per gear timing comp???
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Old 12-17-2009, 12:17 AM   #252
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Doh! You're probably right about the 4.81V as a result of running more boost. I wasn't paying attention to that because I didn't touch boost so disregard that last post.

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Old 12-17-2009, 09:09 AM   #253
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Quote:
Originally Posted by JSarv View Post
Ken I'm going to put you on the spot (for arguments sake)

Sxenario: 11.5-1 target ratio - ipw is @ 16ms at 6000.rpms.

Dwell is changed and read fuel is near 13-1 afr stiill at 16ms at 6000 rpms.
well, first i'd have to say that this is DEFINITELY a theoretical scenario, since i'm going to stick my neck out and say you'll NEVER see such a huge shift in wideband afr from a dwell change.

i base that the utec's method of knock control--rudimentary but effective: yank a user-configurable amount of advance for a user-configurable # of revs. so in a typical knock event you might see 15* suddenly drop down to 9*. then a few log lines later you'll see it go back to 15. despite these large swings in timing i've NEVER seen a repeatable change in AFR. it just doesn't manifest itself in the logs.

now, i think part of the reason for this is due to the fact that our boxers have such a long distance between exhaust valves and turbo. wideband o2 sensors are always post turbo, so that means we have a pretty long distance between the chamber and the meter. in my experience this results in a latency of ~100ms, sometimes more (obviously depending on MAF rate).

i arrived at this figure via logs of the utec's flat foot shifting in action: we can see where the injectors get cut, and we can see how many logs lines later the wideband goes full lean. this typically happens under full load and between 7k and 5k rpms.

let's look at the time differential of a handful of degrees of advance at 5k rpms... 5k rpms is 83 rps, 1 rev (360*) takes .012s, 1* = 0.000033s

so a whopping 10* difference in advance only nets us +/- 0.0003s... that's 0.3ms! compared to the latency involved with TRANSPORTING the spent charge from the chamber to the o2 sensor, it is meaningless (around 0.3%).

i think we'd agree that 10* is a substantial amount of timing, too. although there are CERTAINLY gains to be had by tweaking dwell, i don't think they would be on par with a 10* timing change.

Quote:
Now what is going on? We measure a "guessed" afr based on contents in exhaust. What happens when the burn is pour (good but still not perfect) and dwell is increased to coils limits and ignition quality is increased enough to make the combustion process more efficient.

Are you lean now? or rich then?
again it really gets to the heart of the matter: why do i target a given afr?

we know max power is around 12.5:1. at that point there's enough of a surplus of fuel to make sure that as much oxygen is consumed as possible.

we also know that max flame front speed is around 11:1. this is handy because it will minimize the amount of time it takes to light off the charge. the richer mixture also has more cooling capacity and thus detonation will be comparatively harder to invoke.

somewhere between the two is probably where we'll end up for best torque.

when speaking about afrs i don't find much point in going more exact than +/- 0.2:1 drift. ie, 11.5:1 is substantially the same as 11.7:1 and 11.3:1. there are so many other factors contributing to scatter that trying to dial it down more than that is futile.

far more important is the effect of oxygenates in the fuel or in the ADI, but that's another discussion.

Quote:
Originally Posted by elevenpoint7five View Post
This is the part I was overthinking, how'd you know? Haha!

After reading the thread on IWSTI I have a SLIGHTLY different view of things. Measured AFR will change,
as i've shown above, this depends highly on WHERE you measure the afr change. in the case of the FI subaru with its long exhaust tract, it seems like the combustion, no matter how incomplete in the chamber, has plenty of time to continue in the manifold.

Quote:
however, the true AFR in the cylinder would appear to remain the same. For the sake of technical discussion, you are correct IMO Ken. However, as a rule of thumb for everyone that doesn't care to do the required research, I would say that saying these things can change AFR would be a valid statement.
christian and i both disagree. it just doesn't happen, at least not on these boxers.

Quote:
I suppose we could use measured AFR as an indicator of how well we are doing as far as tuning timing and dwell then. If we see a leaner AFR on the wideband, we have created a more complete burn. Would you agree?
no, i would say that something else has changed between runs to net a leaner afr. looking at the wideband to determine how complete the burn is not going to yield valid results.

in this case, a far better metric would be EGT. lower EGT = more burn in the chamber. however, getting an egt probe with quick enough response is the first challenge. the second challenge is capturing a log of that egt so that you can make informed decisions based on it.

Quote:
Thanks for putting me on the spot seconds before I went to retract/change my previous statement! It's good to learn new things though!


Quote:
Originally Posted by JSarv View Post
Ken is going to bust your balls for that.
awww i missed it!
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Old 12-17-2009, 10:18 AM   #254
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Originally Posted by ride5000
awww i missed it!
I checked myself. So, too bad!
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Old 12-17-2009, 10:48 AM   #255
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To be honest I was having some issues aftewr changing dwell - completely unreleated.

@11.1-1 I'm at 104% idc at 7000 rpms and 23psi...... Lol I'm going to lean it out to around 12-1 after 6k as I typically run in excess of 26psi at redline.

Haha ken I figured you would be razzin his ass. Anyway thanks for the explanation.
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Old 12-17-2009, 12:16 PM   #256
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Lean it out, You dont need the extra enrichment past the trq peak

C
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Old 12-17-2009, 12:39 PM   #257
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Quote:
Originally Posted by Clark Turner View Post
Lean it out, You dont need the extra enrichment past the trq peak

C
I had it around 11.8 at peak and 12.1 by redline but I swapped iat sensors for the gm sensor and had it scaled wrong and tuned for the poor scaling. Once scaled my sd iat comp was way way way low. Then I fixed it and I'm stupid rich. Time for a tuning session.
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Old 12-17-2009, 05:30 PM   #258
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Quote:
Originally Posted by Clark Turner View Post
Lean it out, You dont need the extra enrichment past the trq peak

C
I dont get the reasoning behind this.

At peak tq and low timing cant you run really lean? You know, just like our cars are setup stock holding 14.7 into peak boost. Since your starting the the combustion later and the MAF is comparatively low, doesnt that mean you need less fuel?

Then as you go up in rpm and MAF and increased timing, dont you need more fuel to accomodate the extra oxygen earlier combustion?

Theres probably something im thinking about wrong. just curious what it is.

I use to have my car at 12.5-13:1 at peak tq tapering to 11.5-11.8 at redline.

I guess im thinking more about the volume of fuel, which is already taken car of by the increased IDC's, and not really what Ken asked "why we target a specific AFR".

It makes sense based on everything in the fueling & timing maps. When the timing increases you go leaner, when timing decreases you go richer......

why is it still not making sense to me though?
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Old 12-17-2009, 05:33 PM   #259
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Quote:
Originally Posted by Phatron View Post
I dont get the reasoning behind this.

At peak tq and low timing cant you run really lean? You know, just like our cars are setup stock holding 14.7 into peak boost. Since your starting the the combustion later and the MAF is comparatively low, doesnt that mean you need less fuel?

Then as you go up in rpm and MAF and increased timing, dont you need more fuel to accomodate the extra oxygen earlier combustion?

Theres probably something im thinking about wrong. just curious what it is.

I use to have my car at 12.5-13:1 at peak tq tapering to 11.5-11.8 at redline.

I guess im thinking more about the volume of fuel, which is already taken car of by the increased IDC's, and not really what Ken asked "why we target a specific AFR".

It makes sense based on everything in the fueling & timing maps. When the timing increases you go leaner, when timing decreases you go richer......

why is it still not making sense to me though?
I would think about it in a load aspect as well as flame front speed. At peak torque with the piston moving slower, timing closer to your det threshold and one of the higher calculated loads, you need more fuel per combustion event.
As rpms increase, leaning out the mixture helps speed up the burn, you have extra margin to detonation and your calculated load goes down.

Obviously your fuel flow goes up at rpms increase, but your fuel per combustion event goes down (as is evident in your injector pulse widths). Also, if you look at a VE curve, you'll see that the VE is dropping heavily above 5700-6200 rpm.
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Old 12-17-2009, 08:58 PM   #260
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The TRQ curve is the fuel curve. You need the enrichment during high trq loads. You dont need it before or after this peak. Unless:

1 .You are trying to control EGT with enrichment because the motor will not accept the timing advance that it needs. Advancing timing will reduce egt.

2. You have ****ty octane fuel in which case you have no choice but to run excesivly rich. IE, turn up the boost and tune around it.

3. Your timing curve is so over advanced that your need the enrichment to stop the motor from detonating itself to death.


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Old 12-18-2009, 07:54 AM   #261
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the best thing about leaning it out up top is that it buys you some IDC when you need it most...
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Old 12-18-2009, 10:43 AM   #262
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Technically you can have true maxed injectors under 100% idc.

I leaned mine out up top and kept ipw below 20ms still over 100% idc at 7k though
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Old 12-18-2009, 01:31 PM   #263
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why are the dwell tables and the injector scalar tables based off battery voltage?

does the voltage really swing that much? i've never really looked at it.
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Old 12-18-2009, 01:35 PM   #264
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Ken will explain it - with injectors it is related to time necessary for the coil to operate at a given voltage. Easily desribed it takes longer with less voltage for the coil to operate

With dwell its a voltage drop current increase situation, when voltage drops current increases, ken is way better at explaining the whole induced voltage thing.

I'm not good at explaining and I didn't proof read what I said before lol.

So ignore what I said before.

Last edited by JSarv; 12-18-2009 at 03:58 PM.
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Old 12-18-2009, 01:38 PM   #265
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Quote:
Originally Posted by Phatron View Post
why are the dwell tables and the injector scalar tables based off battery voltage?

does the voltage really swing that much? i've never really looked at it.
Not really, but if the V were to change then the table would no longer be accurate because of what Jerod said. So the best bet was to use a 3D table I would imagine. To be 100% certain you'd have to ask the Subaru engineers though.

Andy
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Old 12-18-2009, 10:43 PM   #266
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Is anyone running this on a big 16g or simalar without utec? (vf39?) I have seen a base map for a vf39, but it was utec specific.

I had a major data loss on my pc and I lost most of my roms. If I can find a good base though I may well just start over on the groupe-n rom.

Anyone?
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Old 12-19-2009, 01:25 PM   #267
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considering its relatively new - your probably going to have to start from scratch.

I started over on my fueling this AM and it took me 2 hours and my STFT's are within -8% to +3% which never ever happened on maf based.

If you don't understand how the fueling works go to RR and read my little confusing writeup about exactly how the ecu determines load.

For anyone that is interested there is going to be a new table release - which may be helpfull for E85 guys and cold start.

Basically before startup it looks at rpms and determines to either use this table or SD load comp table including IAT comp.

If below 500 rpms it uses this table to set load (base fueling before compensations) if above 500 rpms it uses SD load.

So if you are having cold start issues raising the base load value for cranking does help (played with it today)

it is coolant based set load for cranking below 500 rpms

-jerod
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Old 12-19-2009, 02:19 PM   #268
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^Cool that will help many people!
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Old 12-19-2009, 02:46 PM   #269
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hope so!

Will have a SD tune for 02-03 - 100% stock minus TGV deletes. And then will have a stage 2 w/ tgv deletes as well in about a month.

planned on doing it before but now time allows and I have a donor car for this, so should be interesting to see how stage 2 compares as far as driveability.

Stock will be just that, more or less a 100% stock tune minus some timing adjustments.

Stage 2 will be 15psi on stock solenoid and 17.5psi on GM BCS.
Fuel will be 93 mandatory and a custom tune for 91 or Grimmspeed will be available eventually.



Anyway a little OT - This car is a 03 wagon and my friend brought it to me to look at (bought it 2 days ago) 100% stock OTHER than a K&N short ram - Here are the results of a 93 octane 100% stock car with a **** maf based short ram intake JPG is attached.

-Jerod
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File Type: jpg LearningView_SS_12-19-2009 1 30 36 PM.jpg (87.4 KB, 75 views)
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Old 12-19-2009, 02:55 PM   #270
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^Yeah that looks not so nice... Maxxed out at 14.99 system lean codes , has a compression test been done....?...?
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Old 12-19-2009, 03:44 PM   #271
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Simple result of a maf based rom and junk aftermarket intake
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Old 12-19-2009, 03:58 PM   #272
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^yeah the person who put it on probably couldn't figure out why they kept getting a cel...Its funny people think you can change something like the intake and its going to give better hp/tq without any tuning...Poor car
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Old 12-19-2009, 04:28 PM   #273
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yup but it didn't have a ton of miles on the intake (maybe less than 2000) and he just bought it 2 days ago.

-jerod

All fixed now I threw in my stock intake and good as gold.

IAM was solid at 16 though lol.
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Old 12-19-2009, 06:01 PM   #274
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didn't pull too much timing for knock though, when a buddy and I flashed my car over, we ran a log before the reflash and in LV, we saw -3.14 degrees of timing in the higher RPM range... kinda scary.
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Old 12-19-2009, 06:55 PM   #275
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Thanks again Jerod oh and the intake is for sale 25 bucks hahaha
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