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Old 04-04-2005, 09:48 PM   #1
PDXTuning
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Default Some tuning notes (from PPB)

Green tune AFR and Timing AnalyisÖ.

Some time ago during a discussion about AFRs and Timing the topic of more/less boost, effect of AFR, and effect of ignition timing came up. While I was on the dyno last week working on one of our project STIs, I did some playing around with a few of these variables. I was primarily interested to see the direct effect of AFR on the resulting torque, and how that played into both EGTs and ignition advance.

The tune was done on Timís STI, 92 octane pump gas, FP green, the usual Perrin goodies (TMIC, Injectors, BigMaf, etc). I wanted to focus on changes in wheel torque with the same boost level.

I started off with a few baselines, which all netted about the same peak hp and torque (about 340hp, and 285 trq). The map I started was pretty conservative on timing and fuel, with AFRs in the low mid 11s.

As expected, taking a degree of timing away, and taking off about .5 AFR of fuel netted a noticeable change:

Red is baseline, blue is fuel removed and timing removed.



You can see in this graph that midrange torque was improved, especially above 5000 rpm.



Here you can see how the AFR was leaned out a bit, averaging around 11.7 or so, up from about 11.3.



Timing was decreased about a degree, a bit less in a few spots.



Boost was the same for these runs.

Those changes resulted in a good gain, so letís see where it goes If I add a bit more timing back in.



In these, Blue is baseline, Red is timing added.



You can see in this graph that midrange torque jumped up a bit, but the upper end lost some, and most places are nearly the same.



Here you can see how the AFR was about the same.



Here you can see Timing added. The timing at 5000 netted the most gain, while the rest of the timing didnít help much.



Last but not leastÖboost was the same for these runs.

Sure enough, in this case, the slightly leaner and less advanced map made more torque then the more advanced map with more fueling. As I continued the tuning, I pushed both the fuel and timing more. As AFRs got passed 12.0, there were no gains and power, and knock was eaiser to get. The timing was already pretty well dialed, and adding more timing added no more power, and eventually knocked. Even at the highest advance, adding fuel back in (down to about 10.9:1) resulted in now more power. EGTs were almost identical in all of the runs as well, except at the very lean side(12.5:1), where they grew to almost 1700. Most of the runs were right at 1600F after a 4th gear pull. (even at 12:1)

The next task was to work at a lower boost, and see if additional timing combined with the right pressure would yield more power. Unfortunately, this particular Green has the wastegate door turned a few times to keep it shut at high boost, so less boost then about 20psi isnít possible. Once I get another Green based car up on the dyno, Iíll collect and post some more data. As it is, I have 47 pulls, complete with UTEC logs for each to go thru.

Cheers,

Jeff Sponaugle

Last edited by PDXTuning; 04-04-2005 at 10:48 PM.
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Old 04-04-2005, 10:20 PM   #2
T3RMIN4L
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12:1 and 1700F whoa! When are the WI results due in? =]
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Old 04-04-2005, 11:47 PM   #3
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Great, thank you for sharing.
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Old 04-04-2005, 11:53 PM   #4
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awesome, jeff. now i gotta go play around with my car...
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Old 04-05-2005, 12:54 AM   #5
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This was something that we discovered at Turbo-Tunes in Greensboro NC. but I was not entirely sure of at the time. Mark, who runs that place, is a Grand-National genious and can build a heck of a turbo'd mustang... but he's not as familiar with the Subaru platform. So we were learning.

But we did some late-night UTEC road tuning and the bang-for-the-buck seemed to come from lean fuel and conservative timing. Timing advances didn't make a lot of difference, but the leaner condidtions were well felt even with the butt-dyno. And the bad knock results were a lot worse when adding timing than when pulling fuel.

I've been working on a 22 psi setup for my STi ( I have a very safe 20 psi map so far to work with) and trying to maintain richer than 10.9 under WOT. But I think I might pull timing and go for a bit leaner setup to see what happens.

Of course the weather is getting super warm in a hurry here to throw that monkey wrench into the works.
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Old 04-05-2005, 02:47 AM   #6
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The best documented tuning lesson I've seen with something so simple as half an AFR unit and one degree of timing.

I've been mucking around alot with leaner AFR on my dinky VF39, and while I save a bit on gas, I'm not getting much more power going from a general AFR of 10.9 to 11.4, the same 0.5 AFR gain you are talking about. I have found that I can maintain about 3-4 degrees more timing with an AFR of 10.9 than with 11.4. And my super high tech dyno (timing acceleration in 4 gear with the Hydra data logger) says I'm getting a little more power.

I could split the difference, but for now the richer AFR seems safest and I'm sure there's little to be gained from a 0.25 AFR enleanment, a 1-2 degree more of advance, but I'll check it out.

I'vw been told that are no general rule when it come to tuning. I just never believe anybody. I've been trying to experimentally try to figure out the relative contributions of leaner AFR vs. more spark advance. The power peak for gasoline is leveling out as you approach the 12-13:1 AFR mark. How sharp is that peak. Jblaine had a great thread on this awhile back. My sense is that it's still pretty steep in the high 10s to mid 11s of AFR. Once you at or above 11.5:1 your gains in HP/TRQ by raising AFR are not that great--that's when timing is your best friend.

In my range of high 10s to mid 11s AFR, timing and fuel are really flipping back and forth as to which is going to give you more power.

What really throws a wrench into my tuning is what I think is VE. In the peak torque area around 4-5000, the engine is very sensitive to almost any change. A little less fuel here, a little more advance hear, and boom boom I can hear the det start. You graph is convincing me to try leaning out the upper RPM range little more and calling it a day on in the 4-5000 range.

Another beautiful post Jeff, thanks. I'll have to post my $27 detonation listening device on the boards soon and get my web site up so I can post pics and graphs too. I bow to your greatness, some day I'll get down to PDX to meet you.
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Old 04-05-2005, 03:36 AM   #7
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Learned more from this example than all of the pontifications from all of threads put together. Wouldn't mind seeing a graph of the timing too! I see it, just y axis is labeled incorrectly.
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Old 04-05-2005, 06:39 AM   #8
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Quote:
Originally Posted by mnavarro
Learned more from this example than all of the pontifications from all of threads put together. Wouldn't mind seeing a graph of the timing too! I see it, just y axis is labeled incorrectly.
AFR label = ignition advance in that graph...
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Old 04-05-2005, 10:01 AM   #9
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Very good visual example Jeff!

The other thing to add onto Jeff's post, as well as bboy's followup:

As you guys realized, the higher VE is, the less you need to push the car. More importantly, the cars temperment increases dramatically to increases in cylinder pressure due to that VE (I.E. you knock much easier).

It goes to show, while you're tuning, that you'll have relatively "conservative" timing and/or fuel values while VE is high, and you may have a sudden ramp in timing, near the top, while enrichening AFR (for a road race setup it's ideal as it promotes MUCH better egt control.. a very critical thing since you don't want to over work the cooling system on longer track sessions), or a leanout with not so much of a sharp rise in timing (promoting a flatter torque curve with a more gradual drop off) ultimately improving the power band.

Another thing is a rather large increase in transitional torque response running >11:1. Maybe it's just me, but I've always noticed a more "sluggish" feel to a car in the 10's vs a car even at 11.1:1. All good things here folks, keep the conversation going!

Jorge (RiftsWRX)
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Old 04-05-2005, 11:14 AM   #10
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For those curious to read the other thread bboy mentioned, it is here.

Thanks for the post, Jeff.
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Old 04-05-2005, 11:39 AM   #11
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Quote:
Originally Posted by jblaine
For those curious to read the other thread bboy mentioned, it is here.

Thanks for the post, Jeff.
Ahhh yes....

Jorge (RiftsWRX)
www.ProjectWRX.com
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Old 04-05-2005, 12:45 PM   #12
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Kinda puts a fine point on my argument against the www.efi101.com data, eh? But of course, we knew that. Good info, Jeff.

S.

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You don't have to believe me, I'm happy with my tune... But sometime when your on the dyno and ya wanna prove it right or wrong give it a shot and see what ya get, I'll bet you'l be surprised. I know I was... -Alstare

Last edited by n2xlr8n; 04-05-2005 at 12:54 PM.
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Old 04-05-2005, 02:34 PM   #13
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Old 04-05-2005, 03:50 PM   #14
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Quote:
Originally Posted by n2xlr8n
Kinda puts a fine point on my argument against the www.efi101.com data, eh? But of course, we knew that. Good info, Jeff.

S.
was that the one about the guy who said he changed the AFRs in realtime from 9:1 to 16:1 and saw no differences?
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Old 04-05-2005, 04:13 PM   #15
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Quote:
Originally Posted by happasaiyan
was that the one about the guy who said he changed the AFRs in realtime from 9:1 to 16:1 and saw no differences?
Something like that...
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Old 04-05-2005, 12:38 PM   #16
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Post's like these really help me out. Perhaps you can archive them on pdxtunning.com under technical reference?
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Old 04-05-2005, 04:17 PM   #17
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ST with the realtime modifications should make proving/disproving that old thread awfully simple. I read that old thread when it was new and re-read it again now for kicks. It still boils down to a simple, every car is different and tuning isn't getting one point where you want it. It's balancing all factors as best as possible when each one affects the other.
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Old 04-05-2005, 11:25 PM   #18
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Great thread, this is the info I've been looking for!

Steve.
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Old 04-20-2005, 02:48 PM   #19
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bump?
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