Best air/fuel ratio for NA A20

[mushroom_toy]

Alright so this past weekend I installed a PLX M300 wideband in the car and ran the narrowband output for ecu signal as well. Its gonna stay in the car so I went ahead and took advantage of it. Now while im cruising from around 1700-2500 rpm I get a pretty constant reading in the 14:1 area. It fluctuates of course from 14.1:1-15:1. Yall think that is best for daily driving or should I richen it up some. Ive heard a flat ratio of about 13:1 accross the board is the safest and generally what a lot of people tune for, but its not always correct, and will not always get the most out of an engine. On the other hand at idle my a/f r is about 10-11:1 with -1% fuel. If i lean it out too much though of course it wont barely run. What would be the best ratios for daily driving? What would be the best from a performance aspect. Im gonna be taking a look at my last dyno...but tail sniffers arent as accurate as precat sensors so Im not sure what the best route on tuning is at the moment. I want to do it myself though and not spend time/money on the dyno. A street tune that is safe/dependable is fine with me.

Btw just using a piggyback Safc, and working with this engine for now. Of course I have another one Im building and will start all over again with it.

[2drSE-i]

Well 14.7:1 is stoich. It is the most effecient A/F ratio you can run. That being said, you can always lean it out some for fuel economy, and richen it up for more power. Its really all about what you want. The leaner you go, the closer to detonation you get, and the richer you go, the lower your MPG's are gonna go (fouling, etc) Just make sure you adjust your timing as well.

[Tdurr]

^^ he said pretty much as much as i knew on this subject. if ur just DD'in the car then u can lean it out a good bit.

[2ndGenGuy]

You should surf around and look at some example AFR maps from various cars. You'll see that at cruise, you might be able to get away with up 17:1 and even higher sometimes. For the most power, yes tuning near 14.7 is the best, but generally that's for WOT tuning. You want to keep your WOT tune probably somewhere just shy of 14 to prevent any accidental lean detonation. You'll see some tuning guides that say something like 12:1, but I think that's generally for turbo applications. You're safer to go a bit leaner up in the higher RPMs. I think Cygnus might have some AFR maps around for his Megasquirtted A20 setup you could look at. Remember when you see a dyno, that's always for WOT.

Lean it out for low-rpm, low load situations, and richen it up towards the top end just for safety.

EDIT: Here I found one of Cy's maps. kPa being how much load you're putting on the engine, basically how much gas you're giving it...

[mushroom_toy]

You should surf around and look at some example AFR maps from various cars. You'll see that at cruise, you might be able to get away with up 17:1 and even higher sometimes. For the most power, yes tuning near 14.7 is the best, but generally that's for WOT tuning. You want to keep your WOT tune probably somewhere just shy of 14 to prevent any accidental lean detonation. You'll see some tuning guides that say something like 12:1, but I think that's generally for turbo applications. You're safer to go a bit leaner up in the higher RPMs. I think Cygnus might have some AFR maps around for his Megasquirtted A20 setup you could look at. Remember when you see a dyno, that's always for WOT.

Lean it out for low-rpm, low load situations, and richen it up towards the top end just for safety.

EDIT: Here I found one of Cy's maps. kPa being how much load you're putting on the engine, basically how much gas you're giving it...

Yeah thats what Im prob gonna do. Since most of my driving is low rpm (70%) im gonna leave it about where its at between 14-15:1 as for WOT at the moment Ive got it set from 12-13.4:1 which I think is pretty fair. Still gotta set every rpm range up the same way, but I need someone driving for me so I can tune it. XD

[cygnus x-1]

The ideal AFR varies depending on where in the engines operation you are, plus about 273945798457 other variables. But for a typical medium to low compression NA engine:

Idle AFR doesn't much matter. I would try to lean it out until idle RPM starts dropping, then richen it back up a little. 11:1 sounds too rich, but anything close to 13:1 or leaner is just fine.

Under cruising, engines are factory tuned to 14.7:1 to keep the catalytic converter happy and minimize emissions. If you can run leaner at cruise then you can save some fuel. You might not be able to go much leaner at cruise though without also advancing the timing in those areas. Leaner mixtures burn slower so they require more timing advance. I find that 15.5:1 works ok. Any leaner and it starts getting wheezy and kind of nervous feeling due to lean misfires.

At WOT, leaner will tend to burn hotter and produce more power but only up to a point. Go leaner than stoich and power starts going down (as does temperature) because you aren't burning as much fuel as you could be. Unless you have high compression (or really low octane fuel) you aren't going to burn any valves or run into detonation. 13.5:1 is a good target for WOT.

Under hard deceleration I wouldn't bother trying to change the AFR. The engine is using so little fuel it's not worth worrying about.


The map above is not bad but I've altered it a little since then. WOT is a little leaner now and low throttle cruise areas are richer. For whatever reason my engine just doesn't like anything leaner than 15.5:1.


C|

[Tdurr]

good info in here. keep it flowing/sticky this.

[mushroom_toy]

The ideal AFR varies depending on where in the engines operation you are, plus about 273945798457 other variables. But for a typical medium to low compression NA engine:

Idle AFR doesn't much matter. I would try to lean it out until idle RPM starts dropping, then richen it back up a little. 11:1 sounds too rich, but anything close to 13:1 or leaner is just fine.

Under cruising, engines are factory tuned to 14.7:1 to keep the catalytic converter happy and minimize emissions. If you can run leaner at cruise then you can save some fuel. You might not be able to go much leaner at cruise though without also advancing the timing in those areas. Leaner mixtures burn slower so they require more timing advance. I find that 15.5:1 works ok. Any leaner and it starts getting wheezy and kind of nervous feeling due to lean misfires.

At WOT, leaner will tend to burn hotter and produce more power but only up to a point. Go leaner than stoich and power starts going down (as does temperature) because you aren't burning as much fuel as you could be. Unless you have high compression (or really low octane fuel) you aren't going to burn any valves or run into detonation. 13.5:1 is a good target for WOT.

Under hard deceleration I wouldn't bother trying to change the AFR. The engine is using so little fuel it's not worth worrying about.


The map above is not bad but I've altered it a little since then. WOT is a little leaner now and low throttle cruise areas are richer. For whatever reason my engine just doesn't like anything leaner than 15.5:1.


C|

Yeah at idle, I cant seem to get any leaner. If I turn the fuel down on the safc, eventually the afr is right but it bogs so bad its about to die. Im at -3% fuel at 1000rpm, and I get about a 11-12:1 afr right there, so ill prob leave it there for the time being.

[cygnus x-1]

Yeah at idle, I cant seem to get any leaner. If I turn the fuel down on the safc, eventually the afr is right but it bogs so bad its about to die. Im at -3% fuel at 1000rpm, and I get about a 11-12:1 afr right there, so ill prob leave it there for the time being.

I think it's a characteristic of these engines. Mine likes a rich idle too; usually around 12.5-13:1. At 13.5:1 it gets grumpy.

One other thing I was going to mention is that wide bands need to be calibrated periodically. I know the PLX is supposed to be self calibrating but I would still do the calibration in open air every once in awhile.


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[mushroom_toy]

^Yeah I actually did that when I tested it before I bought it, so it should be reading pretty accurately. Plenty accurate enough for me anyway.

[Hauntd ca3]

you would prob find that most motors idle at around 12:1, especially our old ones.
as for power, thats the touchy one.
you actually make more power by running slightly lean than rich.
15 to 15.5:1 or therebouts.
most cars are tuned from factory to be rich as hell at WOT at high revs coz its safer and far less likely to melt a piston coz its burning cooler.
the closer you run to detonating the better the power is a rule of thumb. you can do that with advancing the timing but you end up with a car that a pig to start unless you have the dist regraphed by a pro.
since WOT is something that most of us dont spend much time at( well me anyway) rejetting so its a bit lean in the top end wont hurt , just dont go to lean and melt a piston, burn a valve etc