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Old 06-15-2005, 08:43 AM   #1 (permalink)
 
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Turbolarry - more S-AFC questions w/mods

Ok, turbolarry, just when I thought I had this stuff mastered, I've gone and hit a snag. Back when I had JUST the S-AFC, I was able to tune my car to .91-.93v 02s with a beautiful timing curve that went up to 20-22 by 7500rpm. At the low end, my timing was dipping like it's supposed to at the point of peak torque (~3500-3600), then it would bottom out around 2-3, and finally it would immediately start climbing back up quickly en route to a final of 20-22 like I said before.

But now, I have a 3" cat-back, [email protected], and MR BOV, and I can't seem to get it all right anymore. I also am dealing with quite a significant shift in temp/humidity, so that's another variable that I'm not sure about...I believe it is affecting things, of course, but I don't know which direction it sends my readings.

Anyway, since my logger is in the car, I'll have to give a rough estimate, but it should illustrate the problem:

RPM O2 Tim
2500 .83 16
3000 .89 7
3500 .93 -2 ??
4000 .91 -2 ??
4500 .91 0
5000 .91 4
5500 .91 8
6000 .91 11
6500 .91 14
7000 .91 17
7500 .93 17

As you can see, I have pretty smooth O2 and timing curves, but I have _NO_ idea why my timing is dropping into the negatives and then taking a good 1000rpm to start climbing again. I used to dip to only 2-3 timing, and then start to climb right away, which gave me time to reach 20 by ~7000rpm. Now, since I'm still at 0 near 4500rpm, my timing isn't able to advance far enough...plus, it's lower at each rpm than in the past, which means I'm probably making less power throughout. The problem is that I'm not rich OR lean from 3500-4500, so I don't know how to fix the timing. I could richen everything up to get it at 93, but if you notice 3500, it's already at 93, but still drops to -2 and stays there through 4000rpm.

Any ideas on how to improve this? I'm actually all the way to +3 at 4k and +2 at 4500 as far as the S-AFC goes. I don't start to go negative until 5k on the S-AFC, and then it gradually increases every 500 rpm.

Oh, the one good thing out of all this is that I hit a peak of 1870hz on the Karman readings, so either I'm getting faulty readings, or I'm making 300 or more whp.



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Old 06-15-2005, 11:37 AM   #2 (permalink)
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It's just my $.02;
Well there's good news and bad news... The good news is you mods allow more air in and you can make more power. The bad news is it hot air.
Log at night when it's a little cooler because temperature is a factor. When it goes up, everything goes up, intake temp, IC cooling medium temp., knock... it sucks.
Try adding a little at; 3K, 4K. 4.5K, 5K, 5.5K, 6K, 6.5K, and 7K. Get the O2's to be stable again at .93v across and slowly work a little leaner if you can.
Log it and post it when you can.
Since your already in the positives on the AFC, the ECU is going to give you less timing. To avoid this, and give me more room to play, I threw in 650's, but that's just me.



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Old 06-15-2005, 11:46 AM   #3 (permalink)
 
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Quote:
Originally Posted by turbolarry
It's just my $.02;
Well there's good news and bad news... The good news is you mods allow more air in and you can make more power. The bad news is it hot air.
Log at night when it's a little cooler because temperature is a factor. When it goes up, everything goes up, intake temp, IC cooling medium temp., knock... it sucks.
Try adding a little at; 3K, 4K. 4.5K, 5K, 5.5K, 6K, 6.5K, and 7K. Get the O2's to be stable again at .93v across and slowly work a little leaner if you can.
Log it and post it when you can.
Since your already in the positives on the AFC, the ECU is going to give you less timing. To avoid this, and give me more room to play, I threw in 650's, but that's just me.
Ok, I'll reset everything back to a .93v baseline and see how it goes.

Why do you say the ECU is going to give less timing due to being positive below 5k? Back when I was stock, I had +% below 5k, 0 at 5k, then -% above 5k. The result was less lean conditions before 5k, a quick dip to the timing trough at peak tq, then a quick increase in timing as the rpms increased. Now, I get a slow decrease to a much lower trough in the negatives, and then a very slow response back into the positive. I do have injectors and a fuel pump in mind for maximizing the utility of my S-AFC, but those will be my only additional mods as I try to stay stock-appearing and emissions legal.



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Old 06-15-2005, 12:13 PM   #4 (permalink)
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Quote:
Originally Posted by Warrtalon
Why do you say the ECU is going to give less timing due to being positive below 5k? Back when I was stock, I had +% below 5k, 0 at 5k, then -% above 5k. The result was less lean conditions before 5k, a quick dip to the timing trough at peak tq, then a quick increase in timing as the rpms increased. Now, I get a slow decrease to a much lower trough in the negatives, and then a very slow response back into the positive. I do have injectors and a fuel pump in mind for maximizing the utility of my S-AFC, but those will be my only additional mods as I try to stay stock-appearing and emissions legal.
When it was stock there was a lot less air the ECU saw as compared to now with a turbo-back and MBC. The less air then, even with some positive correction equaled good timing. Now, with more air, it's hot, and the positive correction, it equals less timing. Bigger injectors (with their negative correction) will staighten things right out.



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Old 06-15-2005, 12:42 PM   #5 (permalink)
 
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Quote:
Originally Posted by turbolarry
When it was stock there was a lot less air the ECU saw as compared to now with a turbo-back and MBC. The less air then, even with some positive correction equaled good timing. Now, with more air, it's hot, and the positive correction, it equals less timing. Bigger injectors (with their negative correction) will staighten things right out.
Ok.

I went out and richened everything up significantly from 5-7.5k while leaning out 4-4.5k by 1%. This resulted in .95v from 4-7.5k on every reading and a pretty smooth timing advance that maxed out at 17. I didn't go negative in the low end, and the timing advance began a little earlier. I then leaned out each setting by only 1 and was suddenly back down to .91 in most with a few .93s, but with a nice timing curve still. There was 1 flat spot, but I'm confused as to how i went from .95v to .91v almost across the board with only a 1% change at each level. My guess is that my first run was not long after starting the car while the second run was after everything was heated up fully. When I say "not long after starting up," I don't mean it was cold...my water and oil temps were up to normal operating condition, but I hadn't done any boosting or highway speeds yet, so my IC system wasn't heated up from the hot air yet (probably). I think I'll add 1% from 6-7.5k for now in the effort to keep the lower rpms at .91 and the higher ones at .93 when at full operating condition...or I can go back out tonight when it's cooler (maybe) and see what happens.



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Old 06-15-2005, 09:55 PM   #6 (permalink)
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O2's do fall a little as it heats up;
"When the O2 sensor heats up after several runs, the voltage out put will drop off a little. What was .94v will drop to .92v. This is normal."
From http://www.roadraceengineering.com/i.../autotimer.htm



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