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Ideal afr's under load?

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boost97gst

10+ Year Contributor
3,036
134
Apr 2, 2012
st jacob, Illinois
I was under the impression that about 11:1 for 93 oct was good. Is this too lean? I ask cause i have my knock cel set a 2 degrees. I have a 5858(brand new) and see no cel and logged very little knock at 11psi at 10.9 to 11.2:1 afrs.
When i turn up the boost to 15, i got knock cel around there. Havent logged it yet. I have evo8 mod1 tables loaded as a base point. Should i be pulling timing or going more rich on my afrs like 10:1??
I have to get this afr thing down so i can get one then go after the other ya know. Just want a good afr thatll work and i can pull timing as needed to stave off knock.

All mods up to date
 
The most ideal air to fuel ratio on pump gas is 11.1. Unfortuneatly though, every car is different for what they like. I would honestly start tuning around 10.6 and start from there. This isnt to rich, but leaner then the stock fuel maps. Then you can make your necassary adjustments from there.
 
I have to disagree with you on that. I would turn down the air to fuel ratio so you can make more timing advance. Our 2gs cars are all about timing advance. If he can make his air to fuel ratio lower with higer boost and higher timing advance, that would be ideal. Oppose to higher air to fuel high boost with lower timing advance.
 
Conflicting ideas. Interesting. I see the point of each. I think ill try lowering to 10.6 or 10.8 and evaluate from there. I may still have to pull timing, probably will. Then maybe ill bump it to 11 and pull an extra degree and compare. Dont think the difference will be too much but when i start tuning at full capacity(around 25+psi) these differences will matter alot. I have a setup that i think will do 400whp, its just going to be tricky getting there LOL.
 
I prefer to go for a target a/f ratio when tuning (depending on octane of fuel) than from there adjust the timing.
 
Well bryan, i have to admit from your posts ive read in the past, you know whats up. Thats for sure. Ok, then, ill keep it at 11:1 and pull a couple degrees and see what she looks like. I dont have an egt but i wouldnt think 11:1 is lean at all, probably wont cause a problem with egtemps.
The goal for me is to get one table static and have the other be the variable. It makes alot of sense to adjust timing vs adjusting afrs.
thank you both
 
Start with timing. Different cars like different AFR's, that is true, but that is more of a max power thing, not a safety thing. A given car may like 10.6 better than 11.0, but both are safe on gasoline. You can run a car really lean before you get any knock. You can start melting things before you see knock from a lean condition. Too much timing, or really big jumps from cell to cell will cause knock everytime.
 
Shouldn't be knocking with 15psi and 11/1 AFR.
I find the dsm knock sensor too sensitive when used for knock counts.
I used the link to ignore knocks below 4000 rpm.
I believe 6 counts of knock is the safety region for our cars.

My final solution for the knock sensor was AEM EMS
No more false knocks.
 
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