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Old 04-11-2010, 02:44 PM   #1
68Cadillac
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Default AFR theory: Maximizing Torque (and thereby Power)

I read Jeff Hartman's book
<i>How to Tune and Modify Engine Management Systems</i>How to Tune and Modify Engine Management Systems
. He's a chapter on Air to Fuel Ratio (AFR) theory that speaks directly to boosted engine that are knock-limited.

Lets have a discussion as to what is the best AFR for our engines when we want to make the most power without blowing up. Lets limit ourselves to one fuel: gasoline. 91/93 octane. Since that's what the vast majority of us use.

First some Ratio's:
14.68:1 (~14.7:1) Stoichiometric mix
12.8:1 - Lean best torque
12.2:1 - Mean best torque
11.76:1 - Rich best torque
11.01:1 - Fastest flame speed in cylinder

All five ratios are directly from Hartman's book.

He argues that for boosted engine that are knock-limited, "at a very minimum you are aiming for mean best torque" or 12.2 AFR, "if not rich best torque" at 11.76 AFR. 11.76 AFR has a side benefit of higher cylinder flame speed.

Torque starts dropping off the moment you start to go richer than Mean Best Torque and begins to drop off dramatically after Rich Best Torque. Counter-intuitively the Fastest Flame Speed at 11.01:1 AFR does not produce the most torque, but there is a cliff-like drop off in torque when you start to go richer than that point.

To sum up, Hartman states that 11.76 AFR is the richest one should shoot for. You may have to tune back the boost to get there but you'll get the same torque with better fuel usage than if you turned the boost up and went crazy rich (e.g. 10.8:1).
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Last edited by 68Cadillac; 04-11-2010 at 06:45 PM. Reason: Power <> Torque
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Old 04-11-2010, 03:00 PM   #2
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There is some decent power to be had between 10.0 and 11.0. Most engines that I have worked on pick up 10-15 hp going from 11.0 to 12.0. What happens in that book isn't going to be the gospel. I have tuned a lot of engines and even at 1400whp running it lean isn't the way to go. The general target of 11.3 to 11.5 is fine for 90% of what is out there. If you run them too rich you run the chance of getting fuel down in the ring land and that can cause piston failure. Don't spend to much time looking at it. Tune the engine to a reasonable AFR and don't get greedy with timing.
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Old 04-11-2010, 06:05 PM   #3
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You should give this thread a read. http://forums.nasioc.com/forums/showthread.php?t=673369

The short answer seems to be, there is no magic AFR. But you can find a fuel curve that gives the best combination of power and safety for your combination of engine, turbo, and other parts.
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Old 04-12-2010, 10:38 PM   #4
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The problem with these guides and rules of thumb is that they don't account for differences in engine geometry and the vicissitudes of running a modified production engine on a daily basis. You're also at the mercy of the knock sensor unless you change its monitoring range. So even if x AFR "should" work it may make the knock sensor go off, whether knock occured or not. And most people don't have the balls/wallet to turn off the knock correction.

Over time the cars that last are often the ones with the biggest safety margin in the tune or the ones that have a consistently working knock suppressant (race gas or methanol injection). I don't follow the "best torque" tuning strategy. It's too aggressive and leaves too much to chance when the weather changes.
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Old 09-11-2012, 04:25 PM   #5
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i applaud your quest for information via research. i have that book, and it's solid.

however, years of empirical data on this forum collected through thousands of hours of dyno and street tuning time have shown that subarus tend to prefer a richer afr, and slightly more advanced timing.

on 93 octane, mid 11 afrs are good. lower octane demands afrs in the high 10s for best torque output.

10.8 is not "crazy rich" on a subaru. what works on a 4g63 or an sr20 does not work on an ej2xx. there are myriad theories as to why this is the case (bore/stroke, rod ratio, manifold lengths, head design, etc) but regardless of "why" the fact remains.
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Old 09-11-2012, 04:38 PM   #6
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Quote:
Originally Posted by ride5000 View Post
i applaud your quest for information via research. i have that book, and it's solid.

however, years of empirical data on this forum collected through thousands of hours of dyno and street tuning time have shown that subarus tend to prefer a richer afr, and slightly more advanced timing.
Thanks.

Are you sure you're not mistaking "years of empirical data" for "we've always done it this way"?
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Old 09-11-2012, 06:09 PM   #7
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translation of "years of empiricial data":
after years of tuning subarus and "ACTUALLY" finding the afr that makes
subarus more power and longevity.

yes reading theory is good for a base of knowledge.
but sometimes theory does not actually work in REALITY..

go ahead and tune YOUR subaru to the afrs that the book said
that you should make max torque and see how long your motor last.
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Old 09-11-2012, 07:11 PM   #8
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Originally Posted by 68Cadillac View Post
Thanks.

Are you sure you're not mistaking "years of empirical data" for "we've always done it this way"?
wait.

you mean we can actually tune to different afrs?

and those different afrs might make more or less power, as the case may be?

man, consider my mind blown. nobody in the 38 million posts on this forum has ever suggested that!

a true pioneer.
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Old 09-12-2012, 04:03 AM   #9
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It's a legitimate question, IMO.

My car runs about 11:1 at WOT so I'm not saying that's the wrong approach... but I see no problem with questioning assumptions and investigating alternatives.

One of the guys who mentored me when I was getting started with tuning swears that 12:1 is perfectly reasonable in Subarus. He tunes with less timing than those of us who run 11:1, of course. He just doesn't talk much about this on NASIOC because NASIOC isn't friendly to people who don't adhere to conventions.

Personally, I'm just too chicken. I'm satisfied with my power, and running a 30R on a stock longblock is already tempting fate quite enough, thanks.
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Old 09-12-2012, 05:55 AM   #10
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One of the guys who mentored me when I was getting started with tuning swears that 12:1 is perfectly reasonable in Subarus. He tunes with less timing than those of us who run 11:1, of course. He just doesn't talk much about this on NASIOC because NASIOC isn't friendly to people who don't adhere to conventions.
i think that's bull****.

if you have the data to back something up, then you have the data to back something up. have the intestinal fortitude to share what you have and give back to the community, and take the potshots from the naysayers.

how many folks stood with me when i took on full race's ridiculously inflated claims of how much power their magic headers were going to make?

how many folks were running 20+ psi on a td04 in 2004? or pulled a 4.4 mafv?

how many folks told me a 0.040 gap was going to blow my coils?

how many folks thought the egt "limit" of 1600*f was arbitrary?

how many folks tried running 15 or 16:1 at cruise to test fuel economy benefits?

you can tune a car to run any combustible afr you want. some will have definite advantages over others. the fact remains that the majority of "best results" on subaru FI boxers cluster around 11:1 on 93 octane for best torque. do a little searching on this forum and that fact would present itself, and tell you far more than a number out of a general tuning book. to dismiss the collective wisdom here, and to insinuate that no one else has the balls to try things out themselves and share their results, is disrespectful and myopic.
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Old 09-12-2012, 04:04 PM   #11
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Your browbeating, grandstanding, sarcasm, and bluster do not prove your point. While you demand data from us, why can you get away with "search the forums" and "I did 20+psi on a td04 first" as data?

My evidence comes from books. I should write hypothesis instead of evidence. Technical books. Greg Banish's Engine Management:
Advanced Tuning
; Jeff Hartman's How to Tune and Modify Engine Management Systems. But If you like forums here's a thread on TurboBricks, one from EvolutionM, a thread from AEMPower

The meat of what Banish and Hartman write is that there is an AFR that produces a maximized torque curve a particular forced induction engine can produce on a particular fuel (e.g. 91 octane gasoline). This can vary a bit from engine to engine. But it is somewhere between 12.8:1 and 11.5:1. With forced induction this leans toward the richer side, because it's safer. Naturally Aspirated can be leaner. But both are within that 12.8:1 and 11.5:1 range. Now with your AFR target locked, tune your timing and up your boost til it's not safe anymore.

I know, here at Nabisco, the groupthink has everyone picking the boost target first then dumping loads of fuel in to to prevent knock and backing off the timing. The extra fuel at that level (10.0:1 - 11.5:1) doesn't make more power, it slows the in-piston burn (flame speed) thus preventing knock that you get from picking a ridiculously high boost goal beyond the efficient range of the turbo. The extra fuel is just slowing the flame front and reducing cylinder pressure, keeping knock at bay. Reduced cylinder pressure = less torque. But bragging, "I'm boosting 22.5 psi!" sounds cooler than, "I'm max'n' torque at 11.8 A/F!"

Here's a video from Innovate Motorsports, maker of the LM-1 wideband, o2 product about A/F Ratios and why too rich costs power and wastes fuel. Caution: heavy product promotion.

From Hartman's book page 132:
Quote:
At high loading and wide-open throttle. richer mixtures give better power by making sure that all air molecules in the combustion chamber have fuel present to burn. At wide-open throttle, where the objective is maximum power, all four-cycle gasoline engines require mixtures that fall between lean and rich best torque, in the 11.5 to 13.3 gasoline range. Since this best torque mixture spread narrows at higher speeds, a good goal for naturally aspirated engines is 12.0 to 12.5, perhaps richer if fuel is being used for combustion cooling in a turbo/supercharger engine.
The tuning philosophy I subscribe to goes:
1. Dial In MAF Table
2. Pick AFR (11:76:1 for me).
3. Pick target boost based on the turbo's compressor flow map (19 psi, vf-35 UK STi turbo)
4. Tune Waste Gate Duty Cycle to maximize spool up/prevent surge/prevent over boost
5. Timing Table Tuning Time
6. Tune Waste Gate Duty Cycle part II
7. Timing Table part II
8. Brag on Internet
9. Install new part
10. Repeat

Here's the main problem with our argument. Neither you, nor I, and probably no one here, has the data to prove which tuning philosophy produces more torque. That requires two different tuning maps and dyno sessions on the same car with the same parts on the same dyno under similar atmospheric conditions. That's some coin we'd both have to shell out to get that data. Which one of us will pay a tuner to finalize one map, then tell them to bin it and do it again but another way 'round?

But until you or I do that we can't prove which makes more torque and therefore more power. Right now you've got "Nabisco says" and I've got "Books read". No data for either point.

We can agree about one thing: We both want to maximize torque from our setups.

Last edited by 68Cadillac; 09-16-2012 at 11:49 AM. Reason: engrish be hard, yo
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Old 09-12-2012, 11:44 PM   #12
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Quote:
Originally Posted by 68Cadillac View Post
Your browbeating, grandstanding, and bluster do not prove your point. While you demand data from us, why can you get away with "search the forums" and "I did 20+psi on a td04 first" as data?

My evidence comes from books. I should write hypothesis instead of evidence. Technical books. Greg Banish's Engine Management:
Advanced Tuning
; Jeff Hartman's How to Tune and Modify Engine Management Systems. But If you like forums here's a thread on TurboBricks, one from EvolutionM, a thread from AEMPower

The meat of what Banish and Hartman write is that there is an AFR that produces a maximized torque curve a particular forced induction engine can produce on a particular fuel (e.g. 91 octane gasoline). This can vary a bit from engine to engine. But it is somewhere between 12.8:1 and 11.5:1. With forced induction this leans toward the richer side, because it's safer. Naturally Aspirated can be leaner. But both are within that 12.8:1 and 11.5:1 range. Now with your AFR target locked, tune your timing and up your boost til it's not safe anymore.

I know, here at Nabisco, the groupthink has everyone picking the boost target first then dumping loads of fuel in to to prevent knock and backing off the timing. The extra fuel at that level (10.0:1 - 11.5:1) doesn't make more power, it slows the in-piston burn (flame speed) thus preventing knock that you get from picking a ridiculously high boost goal beyond the efficient range of the turbo. The extra fuel is just slowing the flame front and reducing cylinder pressure, keeping knock at bay. Reduced cylinder pressure = less torque. But bragging, "I'm boosting 22.5 psi!" sounds cooler than, "I'm max'n' torque at 11.8 A/F!"

Here's a video from Innovate Motorsports, maker of the LM-1 wideband, o2 product about A/F Ratios and why too rich costs power and wastes fuel. Caution: heavy product promotion.

From Hartman's book page 132:


The tuning philosophy I subscribe to goes:
1. Dial In MAF Table
2. Pick AFR (11:76:1 for me).
3. Pick target boost based on the turbo's compressor flow map (19 psi, vf-35 UK STi turbo)
4. Tune Waste Gate Duty Cycle to maximize spool up/prevent surge/prevent over boost
5. Timing Table Tuning Time. As much advance one can get with the ECU only rarely dipping into Feedback Knock Correction (FBKC) and never dropping Rough Correction (IAM). Small adjustments in the Fine learning knock correction (FLKC) are okay. Just as long as it's not Max Value (positive or negative).
6. Tune Waste Gate Duty Cycle part II
7. Timing Table part II
8. Brag on Internet
9. Install new part
10. Repeat

Here's the main problem with our argument. Neither you, nor I, and probably no one here, has the data to prove which tuning philosophy produces more torque. That requires two different tuning maps and dyno sessions on the same car with the same parts on the same dyno under similar atmospheric conditions. That's some coin we'd both have to shell out to get that data. Which one of us will pay a tuner to finalize one map, then tell them to bin it and do it again but another way 'round?

But until you or I do that we can't prove which makes more torque and therefore more power. Right now you've got "Nabisco says" and I've got "Books read". No data for either point.

We can agree about one thing: We both want to maximize torque from our setups.
A self tuner should be able to try the two methods. I did. But I calibrated by butt dyno on an NA car.

Problem with the the Internet is they will ask for proof while submitting none. And they'll berate and throw out arbitrary facts and ignore simple questions. Been through it so many times. Brick walls show more intelligence.

And no, I'm not agreeing with you or anybody else here.
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Old 09-13-2012, 12:13 AM   #13
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Quote:
Originally Posted by NSFW View Post
He just doesn't talk much about this on NASIOC because NASIOC isn't friendly to people who don't adhere to conventions.
For example:

Quote:
Originally Posted by ride5000 View Post
i think that's bull****.


Quote:
Originally Posted by ride5000 View Post
if you have the data to back something up, then you have the data to back something up. have the intestinal fortitude to share what you have and give back to the community, and take the potshots from the naysayers.
I hope that means you can show us a couple of your own dyno sheets, showing how much more power you were able to get with 11:1 vs 12:1. Because that would be awesome.

Quote:
Originally Posted by ride5000 View Post
if you have the data to back something up, then you have the data to back something up. have the intestinal fortitude to share what you have and give back to the community, and take the potshots from the naysayers.
I've seen a couple of his dyno sheets (via email) showing 12:1 on pump gas and totally reasonable power. And I've seen other tuners post dyno sheets showing 11.5:1 or leaner, here on NASIOC, and get raked over the coals for allegedly making time bombs out of their customers' cars. We all know exactly what would happen if he posted in PPB.

There are people in the world who crave the respect and admiration of the pseudonymous masses of NASIOC, and there are people who don't. Why would you expect someone in the latter group to even thing about posting something contentious here? It's not going to happen, and frankly it makes me wonder how much interesting, useful stuff doesn't get posted here because of the way NASIOC reacts to anything out of the ordinary.

Quote:
Originally Posted by ride5000 View Post
the fact remains that the majority of "best results" on subaru FI boxers cluster around 11:1 on 93 octane for best torque. do a little searching on this forum and that fact would present itself, and tell you far more than a number out of a general tuning book. to dismiss the collective wisdom here, and to insinuate that no one else has the balls to try things out themselves and share their results, is disrespectful and myopic.
Nobody is questioning that fact. Least of all me. I heartily agree that a search of the dyno sheets posted here will show damn near all of them right around 11:1. And that's why I tuned my own car to 11:1.

But that fact only indicates that 11:1 is popular. And that only tells me that its probably pretty safe.

I do remember seeing one post where a tuner with one of the bigger companies (Cobb or Perrin, I think) said that there was no measurable loss of power until the mixture got down into the mid 10s, or something in that range. But that is the only thing I've seen here (or at RomRaider) where someone described trying multiple AFRs and studying the results.

Let me be clear about something - if I thought 12:1 had a very high probability of making more power with no more risk, I would have at least tried it by now. By my guess is that if there are gains, they're small. And i have no idea what the risks are. And I'm too chicken to experiment with my own motor, so I'm following the crowd on this one, and I'm OK with that.

I know that there are plenty of people who say it's horribly dangerous to run 12:1 at WOT with pump gas, but there are also plenty of people who think that PTFB makes your motor lean out because there's "too much air." Or, you need a tune to safely run a TBE on any Subaru other than the STI. And so on. You know as well as I do that there's a ton of misinformation in this echo chamber. I believe nothing I read here, until/unless I've seen it tested, or better yet tested it myself.

"Everybody does it" is not particularly persuasive, especially in an environment where people are routinely ridiculed for doing unusual things, and more especially when I know a guy who looks an awful lot like a counterexample to the conventional wisdom.

I know you're one of the few who thinks outside of the box around here (I'm running your MBC+BCS setup, for example), so your reaction to this question really caught me by surprise.
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Old 09-13-2012, 01:19 AM   #14
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If safe power could be made at leaner AFRs why would the factory roms run fueling below 11-1? Take the JDM 207 rom from the v8, they have better fuel than we do but they choose to run ~10.4/1 AFR with 17psi of peak boost. Their timing never goes below 27 so you can pretty clearly see they chose timing vs AFR as the preferred method to increase cylinder pressures and make torque.


Here is a log from a JDM motor and you can see it knocking a bit at high RPM since it is running on 91 here in AZ


The extra fuel should drop EGTs while the advanced timing increases cylinder pressures so you can still make good torque without overheating your heads from high EGTs. Leaner AFRs push EGTs up quickly, going from a 11-1 AFR to a 12-1 AFR is a 200-300C increase in flame temperature and that is heat your heads, valves , cooling system has to deal with. Retarding the timing to prevent detonation at these leaner AFRs also pushes up EGTs since the burn spills over into the exhaust ports.





Its your car, do as you like. If the goal is high cylinder pressures to increase torque you can do it with AFR, boost and timing. AFR increases EGTs significantly so using boost and timing to increase cylinder pressures has become a more preferred approach for durable power. I tend to think the engineers at subaru that picked richer AFRs had some good reasons so I just follow their lead when I tune my car.

I like desert track days and non broken motors so I run on the richer side to keep EGTs down. Gas is cheap compared to a new motor.
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Old 09-13-2012, 02:13 AM   #15
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Quote:
Originally Posted by lukeskywrx
If safe power could be made at leaner AFRs why would the factory roms run fueling below 11-1? Take the JDM 207 rom from the v8, they have better fuel than we do but they choose to run ~10.4/1 AFR with 17psi of peak boost. Their timing never goes below 27 so you can pretty clearly see they chose timing vs AFR as the preferred method to increase cylinder pressures and make torque.

Here is a log from a JDM motor and you can see it knocking a bit at high RPM since it is running on 91 here in AZ

The extra fuel should drop EGTs while the advanced timing increases cylinder pressures so you can still make good torque without overheating your heads from high EGTs. Leaner AFRs push EGTs up quickly, going from a 11-1 AFR to a 12-1 AFR is a 200-300C increase in flame temperature and that is heat your heads, valves , cooling system has to deal with. Retarding the timing to prevent detonation at these leaner AFRs also pushes up EGTs since the burn spills over into the exhaust ports.

Its your car, do as you like. If the goal is high cylinder pressures to increase torque you can do it with AFR, boost and timing. AFR increases EGTs significantly so using boost and timing to increase cylinder pressures has become a more preferred approach for durable power. I tend to think the engineers at subaru that picked richer AFRs had some good reasons so I just follow their lead when I tune my car.

I like desert track days and non broken motors so I run on the richer side to keep EGTs down. Gas is cheap compared to a new motor.
A problem with your manufacturer comment is that they never tune cars for optimum power.
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Old 09-13-2012, 05:24 AM   #16
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If safe power could be made at leaner AFRs why would the factory roms run fueling below 11-1?
I give up. Why?

I have a stock 09 LGT ROM in front of me that calls for 9.65:1 at 6000 RPM and up, and I'd love to know WTF the OEM tuners were thinking.

If that's what it takes to be safe, then those of us running 11:1 must be living on borrowed time.
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Old 09-13-2012, 07:51 AM   #17
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Originally Posted by 68Cadillac View Post
Your browbeating, grandstanding, sarcasm, and bluster do not prove your point. While you demand data from us, why can you get away with "search the forums" and "I did 20+psi on a td04 first" as data?
no, see, i'm not the one asking questions. i asked MYSELF these questions, years ago, and then went out and found them out--myself. via 400+ different tunes and thousands of datalogs. i'm not demanding anything. i've made my decisions--not solely because "someone said so," but because i saw it backed up in the data. MY data.

Quote:
But both are within that 12.8:1 and 11.5:1 range. Now with your AFR target locked, tune your timing and up your boost til it's not safe anymore.
do you really feel this is a novel way of tuning?

Quote:
I know, here at Nabisco, the groupthink has everyone picking the boost target first then dumping loads of fuel in to to prevent knock and backing off the timing.
that may be your impression of what everyone does. it is an overgeneralization, and like most overgeneralizations, not correct.

Quote:
Here's the main problem with our argument. Neither you, nor I, and probably no one here, has the data to prove which tuning philosophy produces more torque. That requires two different tuning maps and dyno sessions on the same car with the same parts on the same dyno under similar atmospheric conditions. That's some coin we'd both have to shell out to get that data. Which one of us will pay a tuner to finalize one map, then tell them to bin it and do it again but another way 'round?
why do you insist that no one has collected the data necessary to draw conclusions? this is exactly what i'm talking about when i say "myopic and disrespectful." it is absolutely possible to datalog with sufficiently controlled variables to determine whether or not something makes the car accelerate faster. collecting this data on the street is tedious, but some of us have actually done it.

this doesn't even mention the professional tuners--ones with constant access to dynos--who have given so much of their experience back to this board. you probably have no idea know who jeff sponaugle, or john banks, duncan graham, paul blamire, tim bailey, phil grabow, clark tuner, shiv pathak, lance lucas, nathan from txs, jorge carrillo, jamie from TRP, jermaine at txs, junior from the shop, quirt crawford, or stephen clark, are.

... and that is the problem.

claiming that all they've EVER done is act like ignorant lemmings without ever attempting a (let's be honest here) VERY SLIGHT change in tuning philosophy is utterly absurd, and insulting to their intelligence and ethic.

Quote:
But until you or I do that we can't prove which makes more torque and therefore more power. Right now you've got "Nabisco says" and I've got "Books read". No data for either point.
if i feel sufficiently energetic by the end of the day, i'll fire up the tuning laptop and dump a few thousand logs and a few hundred maps and tuning notes on my website. i'll also post up the logs i've collected from others during private conversations of tuning strategies.

your conclusions can be your own.

Quote:
We can agree about one thing: We both want to maximize torque from our setups.
actually, for me, torque comes secondary to longevity: that's the reason i still have high compression after 95k miles. tuning for 1/4 mile blasts is a different animal. i need my car to get to work every day.
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Old 09-13-2012, 10:36 AM   #18
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I give up. Why?

I have a stock 09 LGT ROM in front of me that calls for 9.65:1 at 6000 RPM and up, and I'd love to know WTF the OEM tuners were thinking.

If that's what it takes to be safe, then those of us running 11:1 must be living on borrowed time.
They put a decent factor of safety on that AFR to protect people from themselves (Derp, 87 is premium right?), if you are careful with putting good fuel in then there is no reason to run that rich.

I have noticed that cars running smaller more restrictive turbines from the factory tend to run excessively rich while cars that came with larger turbos run a touch leaner. Perhaps it has something to do with higher back pressures?

Running leaner also increases the NOx count significantly so the rich AFR could be related to that as well. On my car I target ~11-1 at peak torque then taper down to 10.5-1 at peak RPM, with peak RPM at >8K I feel safer being on the rich side.

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Old 09-13-2012, 11:24 AM   #19
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So good of you to be offended for other people. If it makes you feel any better, your insults and belittling got me right in the feels.

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if i feel sufficiently energetic by the end of the day, i'll fire up the tuning laptop and dump a few thousand logs and a few hundred maps and tuning notes on my website. i'll also post up the logs i've collected from others during private conversations of tuning strategies.
Let us know when you find that energy and dump your few thousand logs, a few hundred maps, and tuning notes to your website. Could you please help us by pointing out the specific maps, logs, and notes that came from the same cars with the same parts where you tuned to different AFR's and achieved a torque difference?
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Old 09-13-2012, 12:35 PM   #20
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Thanks.

Are you sure you're not mistaking "years of empirical data" for "we've always done it this way"?
Absolutely no professional tuners have ever posted significant data or engaged in conversations about tuning strategies on this site in the last decade. Nor have said tuners ever tuned any car other than a Subaru..... There is obviously more than one way to skin a cat. Most ways have been explored years and years ago....

Last edited by quazimoto; 09-13-2012 at 01:08 PM.
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Old 09-13-2012, 01:39 PM   #21
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Could you please help us by pointing out the specific maps, logs, and notes that came from the same cars with the same parts where you tuned to different AFR's and achieved a torque difference?


yeah.
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Old 09-13-2012, 04:12 PM   #22
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Here's a quote from article from AutoSpeed Magazine. The last sentence in the quote is interesting.

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A naturally aspirated engine should run an air/fuel ratio of around 12 - 13:1 at peak torque. The exact air/fuel ratio can be determined by dyno testing, with the ratio selected on the basis of the one that gives best torque. Rich air/fuel ratios can be used to control detonation, and this is a strategy normally employed in forced induction engines. Thus, on a forced induction engine, the mixture should be substantially richer: 11.6 - 12.3:1 on a boosted turbo car and as rich as 11:1 on an engine converted to forced aspiration without being decompressed. As is also the case for ignition timing, the air/fuel ratio should vary with torque, rather than with power.
Click for larger image

Most factory forced induction cars run very rich full load mixtures, with 10:1 being common. This is done for engine and cat converter safety reasons - in case an injector becomes slightly blocked, or the intake air temperature rises to very high levels. These cars will normally develop more power if leaned out. Note that emissions testing does not normally take place at full throttle, so full load emissions can be high without legal problems.

In the engine operating range from peak torque to peak power, a naturally aspirated engine should be slightly leaner at about 13:1, with the forced induction factory engine about 12:1 and an aftermarket supercharged engine staying at about 11:1.
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Old 09-13-2012, 04:20 PM   #23
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Here's a FAQ from High Performance Products out of Australia about their superchargers.

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An engine must have the ideal air / fuel ratio to produce maximum power.
Again every engine is different, but generally the best power is produced at around 12 - 12.5 : 1.
Additional fuel does not usually control detonation nor produce more power. One of the best methods of controlling detonation is octane.
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Old 09-13-2012, 04:24 PM   #24
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What your ROM cells say and what the ACTUAL AFR is....is a different story. The oem tuners may have had to command a 9.5 AFR to get a 11.3 AFR at the o2 sensor location. At least thats how my rom is. Ive got a 10.5 afr commanded at full boost 5000 rpms and up. Its running about 11.3-11.7 actual afr tho.
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Old 09-13-2012, 04:26 PM   #25
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Here's one from ImportTuner Magazine.

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Tuning the fuel boils down to setting some targets for your AFRs and doing your best to hit those targets. For naturally-aspirated cars, AFR's should usually range from 14.7:1 at idle and very light throttle, 14:1 to 13:1 at part throttle, and around 12.5:1 at wide-open throttle.

The AFR targets for a forced-induction car are a little different. Normally, the off-boost targets will be the same as naturally aspirated engines, but under boost they usually are tuned to run rich, which leaves extra fuel in the chamber for cooling and reduces the chances of detonation. On crappy pump gas (91 octane), most tuners we know tune using conservative AFR targets under boost (around 11:1 to 12:1).
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