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Old 08-12-2008, 04:02 AM   #1
williillii
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air/fuel ratio + tuning question

I recently installed a wideband in my car, and started playing around with tuning it. It seems that alot of people here agree that 11.5:1 is a good afr to run on pump gas at WOT. My car runs kind of lean, and I'm wondering if it is safe or not.

The car is a 95 GST, relevent mods are cone filter,fp intake, 14b turbo w/hard pipe smic +1g BOV, hallman pro mbc, stock 450cc with an SAFC2 and PLX m300 wideband to make adjustments. 93 octane fuel

During a third gear pull, turbo hits full boost by the late 3000rpm range and the car wants to run at 12.0:1 at first, then may lean out to 12.3:1 by redline. This is at 9ish psi (wastegate spring), it does roughly the same thing at 15psi, it might get .1 leaner. I can't log knock since I have a 2g, but the timing advance drops to 10 when I step on it, then steadily rises to 18 or 19 by 7000rpm. I also checked the plugs for any signs of damage and found none after several pulls at 15psi.

If I add fuel with the SAFC to bring it down into the 11.5:1 range, the car bogs and gets flat spots in the timing, which maxes out at 15* by 7k. Also to add enough fuel at 6500+ I have to set the SAFC to +19 or so, which seems to induce fuel cut.

cliffs : Car runs like crap at 11.5:1 afr, much better at 12-12.4:1, is this safe with 93 pump gas?

Any input is appreciated, thanks!
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Old 08-12-2008, 04:31 AM   #2
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Re: air/fuel ratio + tuning question

On pump gas i would try and keep it around 11.0-1 just to be safe. Anything above 11.0-1 on pump gas is just asking for trouble.
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Old 08-12-2008, 04:43 AM   #3
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Re: air/fuel ratio + tuning question

Woah, 12-12.4 for wot is too lean...
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Old 08-12-2008, 10:39 AM   #4
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Re: air/fuel ratio + tuning question

You need a fuel pump and/or a set of injectors.

You are compensating for the AFR by having to turn up the AFC. So the ECU thinks you are seeing much more airflow than you are and is not advancing the timing to where you need it. If you run a larger injector then you'll be able to dial back the AFC, get the AFR in the right spot, but the timing will stay up better.
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Old 08-12-2008, 12:21 PM   #5
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Re: air/fuel ratio + tuning question

You will make more power with a 12 something AFR so of course it wont feel as good when you richen up the ratio, but anything leaner than 11.5 is too lean on straight pump gas....11.2- 11.4 is the best safest AFR that still gives good power from my findings with 93octane. 11.0 and richer starts robbing too much power progressively worse the richer you go imo.
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Old 08-12-2008, 12:29 PM   #6
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Re: air/fuel ratio + tuning question

When I got my car tuned in with the dyno, the person who tuned it actually found the most power at around 9.5-9.8 on pump gas. We tried a bunch of different AFR's, and the 9 range seemed to work best because of timing, knock and all that jazz.
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Old 08-12-2008, 03:45 PM   #7
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Re: air/fuel ratio + tuning question

It's not that it doesn't feel good at 11:1, it feels downright awful. The car surges like crazy, and feels like it has 75% of the power. When I zero out the AFC it runs so much smoother and give me 5* more timing..

I guess what Mike 99GSX is saying sounds about right, I plan on installing both a fuel pump and some 660s as soon as get my FMIC piping run.

I'm still wondering why I'm getting almost 20* of timing at redline with the 12.4:1 ratio though, I was under the impression that if the motor is knocking it will not advance/pull timing, which doesn't really seem to be happening? And am I really pushing the stock fuel system to its limits at 10PSI on a 14b turbo?
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Old 08-12-2008, 05:06 PM   #8
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Re: air/fuel ratio + tuning question

No, you shouldn't be maxing out your fuel system. If what you are saying is true, you basically have a stock setup, with stock-ish boost pressure.
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Old 08-12-2008, 05:09 PM   #9
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Re: air/fuel ratio + tuning question

Quote:
Originally Posted by aworldsdeath
When I got my car tuned in with the dyno, the person who tuned it actually found the most power at around 9.5-9.8 on pump gas. We tried a bunch of different AFR's, and the 9 range seemed to work best because of timing, knock and all that jazz.
It probably only made more power because being that rich allowed more timing and or boost on your particular setup under whatever conditions the tune was in during the time the test was being performed.

Nobody should run around that rich, actually most cars will being knocking just because of being that rich. I know thats around factory level of richness, but 90% of us keep our pump gas tunes in the High 10, low 11 AFR range.

Quote:
Originally Posted by williillii
I'm still wondering why I'm getting almost 20* of timing at redline with the 12.4:1 ratio though, I was under the impression that if the motor is knocking it will not advance/pull timing, which doesn't really seem to be happening? And am I really pushing the stock fuel system to its limits at 10PSI on a 14b turbo?
I dont know why your car is doing what it is doing, you do need to make sure your fuel system is up to par though, But 12.4 AFR on pump gas is simply too lean. Theres nothing else to say about it than that.

How do you know the motor is not pulling timing, are you logging it correctly? It doesnt appear you have dsmlink, and you know that 2gs dont display knock on the logger, you have to look for any dips in the timing curve.

SAFCs have been known to increase timing advance and/or cause other wierd problems about a tune especially when you use them to hide airflow to run bigger injectors... I dont know if you have bigger injectors but what I do know is something is off with your settings, and you are way too lean with increased timing advance over what the stock map should give.
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Old 08-12-2008, 05:12 PM   #10
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Re: air/fuel ratio + tuning question

At only 15psi you can get away with 12:1, once you start to push the envelope is when you need to be a little richer.
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Old 08-12-2008, 05:38 PM   #11
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Re: air/fuel ratio + tuning question

Quote:
Originally Posted by Black_ bullet
How do you know the motor is not pulling timing, are you logging it correctly? It doesnt appear you have dsmlink, and you know that 2gs dont display knock on the logger, you have to look for any dips in the timing curve.
Im logging with Evoscan. I would post a log, but Evoscan is utter trash for the EPROM ECU and only gives me like 5-6 samples a second, so it is useless for anything other than one parameter at a time. I'm watching the timing in real time on a graph, like I said it drops to 10 when I punch it, then steadily climbs to 19 degrees by redline.

Quote:
Originally Posted by Black_ bullet
SAFCs have been known to increase timing advance and/or cause other wierd problems about a tune especially when you use them to hide airflow to run bigger injectors... ...with increased timing advance over what the stock map should give.
I have stock 450cc injectors. The SAFC is zero'ed out in the aformentioned situation. What should the stock timing maps look like? 19 degrees is too much you say?

Quote:
Originally Posted by 93_GSX
No, you shouldn't be maxing out your fuel system. If what you are saying is true, you basically have a stock setup, with stock-ish boost pressure.
Yep, it's basically stock. Which is why I'm wondering why its so lean.

Thanks for all the help guys!
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Old 08-12-2008, 06:13 PM   #12
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Re: air/fuel ratio + tuning question

You should definitely pick up a fuel pump soon, and look for a decent deal on some evo 560s. Check out evolutionm.net, I'm sure you won't have to drop more than $125, and it may be worth tossing them in before your fmic. Just a thought.
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Old 08-12-2008, 07:02 PM   #13
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Re: air/fuel ratio + tuning question

Quote:
Originally Posted by williillii

I'm still wondering why I'm getting almost 20* of timing at redline with the 12.4:1 ratio though, I was under the impression that if the motor is knocking it will not advance/pull timing, which doesn't really seem to be happening? And am I really pushing the stock fuel system to its limits at 10PSI on a 14b turbo?
The reason you're getting so much timing is because you are dialing back the airflow signal on the AFC (making the knob more negative) when it runs 12.4:1. The less airflow the ECU then the more it will advance the timing as long as the engine doesn't knock. You're getting away with running the car that lean and not knocking due to the low boost level.
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Old 08-12-2008, 07:29 PM   #14
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Re: air/fuel ratio + tuning question

Maintenance

Please check off the following if you have completed them:
  1. Boost leak test
  2. Checked your spark plugs/wires
  3. Checked/replaced fuel filter
  4. You are hitting right about 20 inches of vacuum at idle
  5. Perform a compression tesy
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Old 08-12-2008, 07:47 PM   #15
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Re: air/fuel ratio + tuning question

At WOT I run 22psi tapering to 16psi by redline on my 14b, My afr is 11.5:1 and my timing is set at 17 degrees, I have no knock anywhere and plan to try to reach 12:1. I have a FMIC and FRH intake manifold. I have found that the leaner I go with as much boost as the 14b is delivering, the more power I make. Timing and too much boost is a greatway to fuck your car up. Lean is mean, find your max acceptable boost level, dial-in your afr, and add timing until you knock. Or go fuel, boost, then timing. Timing is always dead last on my list.
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