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Old 12-06-2008, 12:22 AM   #1
williaty
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Default What's Your Target AFR?

If you have an NA engine (no turbos, supers, N2O, etc) and have tuned it yourself or had it tuned, what is your target AFR at WOT?

Just seeing how other people are handling this.
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Old 12-06-2008, 12:28 AM   #2
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im going for low-mid 13ish in the WOT lower RPM cells and getting to 12.4 @ WOT 4400RPM to redline . Honestly, i am shooting for that because it the MBT in theory. But i think i got that info from you, or someone on here/RR forum. So I might be in the same boat as you as far as fueling strategy. I meant to ask you, what was your factory O2 sensor reading compared to your WB at high load (WOT) above 4k RPM? Mine wasnt as far off as i expected. far enough to make a difference, though.

Last edited by GrundleJuice; 12-06-2008 at 12:33 AM.
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Old 12-06-2008, 11:16 AM   #3
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12.56 in high load / high RPM, tapered all the way to high 13's in low load/RPM.
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Old 12-06-2008, 09:48 PM   #4
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wikipedia is claiming , In Naturally Aspirated engines powered by octane, maximum power is frequently reached at AFRs ranging from 12.5 - 13.3:1 or λ of 0.85 - 0.901.
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Old 12-08-2008, 12:29 AM   #5
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I find it hard to believe we've got only 4 tuned RSes on here...
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Old 12-08-2008, 07:22 PM   #6
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Ty, have you asked over at RR forum?
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Old 12-08-2008, 07:24 PM   #7
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What percent of the people with CAIs would you say actually know what MBT stands for?
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Old 12-08-2008, 07:30 PM   #8
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Quote:
Originally Posted by LetItSnow View Post
What percent of the people with CAIs would you say actually know what MBT stands for?
Not nearly enough.
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Old 12-08-2008, 08:07 PM   #9
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Which MBT? There are two relating to tuning, you know.
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Old 12-08-2008, 08:17 PM   #10
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i am only familiar with minimum best timing pertaining to ignition. ? whats the other?
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Old 12-08-2008, 08:19 PM   #11
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Maximum Best Timing

Mean Best Torque
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Old 12-08-2008, 09:04 PM   #12
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u mean MINIMUM best timing right?
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Old 12-08-2008, 09:21 PM   #13
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my AFR getting a reading from 14.1 ~ 14.7 is it okie with it?
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Old 12-08-2008, 09:36 PM   #14
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Well now, that's an interesting question. The internet has about the same support for Maximum as it does for Minimum. The only textbook I have in the house that refers directly to MBT in relation to timing defines it as "Maximum Brake Torque". So I don't think we're going to resolve this one easily.
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Old 12-08-2008, 09:46 PM   #15
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im looking it up in my ase text now , but ive allways known it as minimum best timing , refering to advancing the timing only so far as would provide maximum power output.
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Old 12-08-2008, 09:50 PM   #16
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ahh it seems we are both correct.

and to all those that didnt weigh in its cool

(13) MBT:

minimum best timing, the industry-recognized expression for the ignition
timing (spark occurence as degrees in advance of top dead center, or
"spark advance") that yields best torque (maximum brake torque) for the
engine.
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Old 12-08-2008, 09:55 PM   #17
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well accually i think i was more right but whatever
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Old 12-08-2008, 10:09 PM   #18
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I was specifically referring to "mean best torque" but i think max best timing, min best timing and mean best torque are different names for the same thing.
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Old 12-08-2008, 10:13 PM   #19
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i think they are different . look at the definition , they define minimum best timing , just read the definition. maximum best timing is like what you would think it would be called and alot of people call it that. but as far as ase certification goes its minimum best timing , and mean best torque is a result of minimum best timing
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Old 12-09-2008, 12:55 AM   #20
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Quote:
Originally Posted by watchunglava View Post
i think they are different . look at the definition , they define minimum best timing , just read the definition. maximum best timing is like what you would think it would be called and alot of people call it that. but as far as ase certification goes its minimum best timing , and mean best torque is a result of minimum best timing

Wha??? Mean Best Torque is a reference for the AFR that should achieve the most torque. Min/Max best timing dont refer to AFR's, do they? I thought they were in reference to actual spark advance before TDC. Now im thouroghly confused and tired.
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Old 12-09-2008, 01:03 AM   #21
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ohh true lol !!! i dont know some random guy was like does anyone know what mbt is lol . and wility was like which one , talking about tuning , i guess it went off topic. god darn cold air intake havin freaks!
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Old 12-09-2008, 11:00 AM   #22
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Quote:
Originally Posted by williaty View Post
If you have an NA engine (no turbos, supers, N2O, etc) and have tuned it yourself or had it tuned, what is your target AFR at WOT?

Just seeing how other people are handling this.

13:0.1

That has always been my target for N/A performance with basic mods (Intake, exhaust, header). Once you mod to the point of having to go with a different octane, I would no longer go by air/fuel ratio as a primary tuning measure but exhaust gas temperature (Along with air/fuel ratio).
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Old 12-09-2008, 07:30 PM   #23
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Quote:
Originally Posted by Kevin Thomas View Post
13:0.1

That has always been my target for N/A performance with basic mods (Intake, exhaust, header). Once you mod to the point of having to go with a different octane, I would no longer go by air/fuel ratio as a primary tuning measure but exhaust gas temperature (Along with air/fuel ratio).
That's interesting. What octanes do you suggest using a pyro reading along w/ AFR for tuning and why? are you targeting just rich of peak for most torque? If not, what do you target in terms of EGT?
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Old 12-09-2008, 08:55 PM   #24
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Quote:
Originally Posted by RaceFaceXC View Post
That's interesting. What octanes do you suggest using a pyro reading along w/ AFR for tuning and why? are you targeting just rich of peak for most torque? If not, what do you target in terms of EGT?
The EGT is just a poor man's O2 sensor. It's in no way any better than a WBO2, regardless of octane. The reason an EGT gauge can be useful is that EGTs peak at stoich. So you find the fueling that returns peak EGT, then lean out or enrich the mixture until the EGT drops the amount the engine manufacturer recommends. The amount of EGT drop per lambda change varies from engine to engine, so without a published spec from Subaru, or without having both a WBO2 and a EGT to calibrate the EGT results, EGT change has no meaning.

Wait a minute, you're an airplane mechanic, right? Adjusting fueling based on EGTs was developed initially with piston aircraft engines. Google "Wright Aeronautical Division Recommended Leaning Procedure".
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Old 12-09-2008, 09:56 PM   #25
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Quote:
Originally Posted by williaty View Post
The EGT is just a poor man's O2 sensor. It's in no way any better than a WBO2, regardless of octane. The reason an EGT gauge can be useful is that EGTs peak at stoich. So you find the fueling that returns peak EGT, then lean out or enrich the mixture until the EGT drops the amount the engine manufacturer recommends. The amount of EGT drop per lambda change varies from engine to engine, so without a published spec from Subaru, or without having both a WBO2 and a EGT to calibrate the EGT results, EGT change has no meaning.

Wait a minute, you're an airplane mechanic, right? Adjusting fueling based on EGTs was developed initially with piston aircraft engines. Google "Wright Aeronautical Division Recommended Leaning Procedure".
Yes I am. Thats why i asked what his theory and strategy for using EGT was. I use EGT all the time to adjust fuel mixture for all kinds of reasons. Economy, peak power output, peak cruise speed, burning some crap off a dirty plug, etc etc. But its not a sceintific technique when we do it, its just a use of fuel mixture to "get close" to what were going for. I was curious how Kevin uses it to tune. I had doubts about how accurate and precise it could be but i was giving him the benefit until i knew otherwise.
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