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Old 12-30-2007, 08:54 PM   #1
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Default how do you determine which AFR's to run?

I've heard so many different schools of thought on this that I don't really know what's right or wrong anymore. A well known miata shop owner told me today that 13.4 was too lean for 100kpa full throttle and told me to go 11.0:1 or richer from 6psi+.

if someone has a target ego table, that would be great too, but please explain what ratios at rpm and load, and why.
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Old 12-30-2007, 09:03 PM   #2
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11.0:1 or richer?! no.



there's no reason to ever get close to 11.0:1. boost or not. its a waste of gas and does nothing. its doesnt cool the charge, slow the burn or anything but waste gas.

the point of the extra fuel is to slow the burn and to add some additional cooling to prevent detonation. Between 12-12.5:1 is perfectly safe, fool around with what gives you the best torque that you are happy with.

From what I've seen on the dyno the stock AFR gets to 12.5:1 at WOT N/A, which I don't see a problem with being between 13-13.5:1 to give you more power. The same car at 11:1 or richer would most likely be down 10hp.

detonation can be dealt with by your spark tuning.
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Old 12-30-2007, 09:05 PM   #3
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this is what i currently run
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Old 12-30-2007, 09:08 PM   #4
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Thanks a ton for that, imma use it when I get my MS running.



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Originally Posted by Braineack View Post
11.0:1 or richer?! no.



there's no reason to ever get close to 11.0:1. boost or not. its a waste of gas and does nothing. its doesnt cool the charge, slow the burn or anything but waste gas.

the point of the as fuel is to slow the burn and to add some additional cooling. between 12-12.5:1 is perfectly safe, fool around with what gives you the best torque that you are happy with.

IIRC the stock AFR gets close to 12:1 at WOT N/A, which I don't see a problem with being between 13-13.5:1 to give you more power.

detonation can be dealt with by your spark tuning.
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Old 12-30-2007, 09:08 PM   #5
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I've read several different numbers as well so I'd start with an AFR around 12 like brain and adjust only for knock (assuming your timing is okay and probably making it a bit richer if you get knock since you'll be tracking it) or even better, for max power on the dyno (within reason). As long as you don't have detonation and are running a reasonable afr, I don't think there is one number that is perfect for all setups.
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Old 12-30-2007, 09:23 PM   #6
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i like to be richer, like 11.8 in boost. from my own observations 12.5 doesn't gain you anything but more fuel effiecency in boost. look at an oem a/f chart, i'd rather lean towards safer than try to get couple more horses
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Old 12-30-2007, 09:30 PM   #7
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Braineack, do you have your ego correction enabled up too 100kpa?

Btw, I like how you scaled your table, you just gave me a whole new insight on how to make mine better.
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Old 12-30-2007, 09:43 PM   #8
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I'm pretty sure my ego limit is 255kPa

10% authority with 1% step, starts at 1500RPM.


that was an old targets table....i'm using this one now:

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Old 12-30-2007, 09:44 PM   #9
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Quote:
Originally Posted by Mach929 View Post
i like to be richer, like 11.8 in boost. from my own observations 12.5 doesn't gain you anything but more fuel effiecency in boost. look at an oem a/f chart, i'd rather lean towards safer than try to get couple more horses
That's why my GReddy setup made ~20-ft-lbs more torque.

In all seriousness, going too rich doesn't gain all that much safety either. There was a good article on Innovate's site about how adding more fuel beyond a certain point really doesn't do anything for you. Edit: I found it.
http://www.innovatemotorsports.com/resources/rich.php
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Old 12-30-2007, 09:46 PM   #10
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i was running my other 94 which is stock with my AEM WB and the AFRs dipped into the high 10's & 11's at WOT above 4k
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Old 12-30-2007, 09:51 PM   #11
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Quote:
Originally Posted by paul View Post
i was running my other 94 which is stock with my AEM WB and the AFRs dipped into the high 10's & 11's at WOT above 4k
B/c it goes into open loop and runs rich for safety to take into account different ambient temps, elevations, etc... My stock 91 did the same on the dyno. That's where DIY picked up power with their MS PNP by tuning this area better.
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Old 12-30-2007, 10:57 PM   #12
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Quote:
Originally Posted by brgracer View Post
That's why my GReddy setup made ~20-ft-lbs more torque.

In all seriousness, going too rich doesn't gain all that much safety either. There was a good article on Innovate's site about how adding more fuel beyond a certain point really doesn't do anything for you. Edit: I found it.
http://www.innovatemotorsports.com/resources/rich.php
could also be why you needed a new motor
i looked at some logs and i'm losing boost in that range, it spikes up, then dips and creeps back up later. i've also talked to a couple tuners and they say to load up with fuel around peak torque and little before to spool the turbo faster.
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Old 12-30-2007, 10:57 PM   #13
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Quote:
Originally Posted by Braineack View Post
I'm pretty sure my ego limit is 255kPa

10% authority with 1% step, starts at 1500RPM.


that was an old targets table....i'm using this one now:

[img]http://boostedmiata.com/MS/afrtargets1.JPG[/i]
So you have open loop disabled entirely?
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Old 12-30-2007, 11:18 PM   #14
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whoops no, looks like i hit open loop at 110kPa.
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Old 12-30-2007, 11:48 PM   #15
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Why dont you have it tweak while in boost as well? I mean your afr table is setup for it.

I know I have read somewhere, some people say its not good, but I wonder why not. If its setup right, it should only be a benefit. If you think it will have to much authority, you can tweak the sensativity with the ego limit.

In my mind right now. I figure ill have it run correction up to 200kpa. But ill set the "change ego limit above" in Lamda AFR settings to 101. Then the Ego limit to 5. That should change the authority from 10 to 5 when in boost.

What is open loop 02 correction(found in open loop settings)? I thought that o2 correction only happens in closed loop and if the car is in open loop no correction is made.
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Old 12-30-2007, 11:57 PM   #16
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boost is easy to tune. If you watch your logs, the fueling just needs one row to read across. The rest of the rows (below 3000RPM) is just to smoothly increase the AFR to 12:1.

for example, I typically see this line while WOT:

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Old 12-31-2007, 12:10 AM   #17
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I edited my post, added more questions.

I also understand your VE table, but still dont understand why you wouldnt want the megasquirt to tweak the fuel while in boost to reach your afr targets.
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Old 12-31-2007, 12:18 AM   #18
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i see a flat AFR in boost, no reason to have the computer make corrections. while cruising, the smallest change in vacuum can dramatically change the fuel.
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Old 12-31-2007, 12:35 AM   #19
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So why do they call it open loop o2 correction, if it disable correction above that number?

Some of the things are pretty confusing in the megasquirt.
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Old 12-31-2007, 01:22 AM   #20
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its just open loop mode, which means no o2 corrections, and just fueling based off the map.
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