Ideal air fuel ratio

[1WheelWonder]

Hopefully my plx m300 will arrive shortly so I can start tuning. My question is what is the ideal air fuel ratio for cruising, boost, etc. Any help will be appreciated.

[virus77]

Idle: 14.7 (o2 should take care of it if but some tinkering might be needed for solid idle)

Cruising: 14.7 ish (your o2 sensor and factory ecu should take care of that)

WOT: 11.5 - 12.0 is a good place to aim for

Part throttle boost: should be around 11.5 - high 12's. this is what i have seen from factory turbo cars when they get into boost in part throttle/boosting situations.

[1WheelWonder]

Thanks Virus

[fiznat]

The thing to remember about AFRs is that 14.7:1 is ALWAYS stoich (the point where every fuel molecule has the correct amount of oxygen molecules available for complete combustion). The reason we change the fuel RATIO in boost is because the extra fuel is needed to cool the combustion chamber. This fuel is not burnt, it is simply used as a cooling agent. In order to effectivly cool a boosted engine, you should be running ratios in the 11's or low 12's at least while in boost. Off boosting you will be perfectly fine right around stoich.. idle you can even go a little leaner (I've seen idles at 16:1 and higher). For accelerating and light boost applications, simply split the difference between your off boost 14.7:1 and your full boost 11:1 or so. Err on the rich side always, and you will be perfectly fine.

[virus77]

To add to that, I coast at around 15.4 or so and idle around there too, it gets you better gas millage. 14.7 is actually the AFR that gives the least emmissions, thats why stock cars aim for that on idle and cruising.

[1WheelWonder]

Thanks guys, now i know where to be at during tuning, I appreciate it.

[Florida240sx]

Thanx, me too.

[Florida240sx]

Is 11.5-12.5 safe for boost? While I'm in boost at WOT?

[Craving4Boost]

Is 11.5-12.5 safe for boost? While I'm in boost at WOT?

12.5 is the IDEAL AFR for boost yet we all want to stay on the rich side to be safe. unless you have water injection or alky injection then i wouldnt recommend having 12.5 on full boost.

[1WheelWonder]

When at idle are you all afr's rock solid or do they bounce around a little.

[Craving4Boost]

should bounce around a bit. ive never seen rock solid before haha..

i know sometimes mines get rich so i have to lean it out

[mirra32]

MY CAR IS TILL N/A SO...... when i let go of the gas and coast the car, the display throws LEAN for about a second or two....is that normal.....what about in a turbo application...if not normal....is it ok for now...and with a SAFC i would be able to fix that, if not normal that is.

eric

[Craving4Boost]

in turbo you wouldnt want it to be rich because that means your BOV is letting out all the air. so it should lean up a bit when your letting off the GAS. i think thats right, right? should be the same for NA

[DRIFTEADOR]

also, over a certain rpm, 3000 iirc, fuel is cut off altogether on deceleration.

[virus77]

When you lay off the gas and decel in gear the car is going to run lean, either turbo or non turbo its the same, right around 19 or 20:1 AFR. There is always fuel being put in even on deceleration. Under 3 grand I get 1% duty cycle and over 3 grand on decel I get 2% duty cycle, so the the ecu does in fact put fuel in to achieve around a 20:1 AFR on decel.

Oh and at idle it usually bouces from a 14.5:1 to about a 15:1, but sometimes it stays amazingly stable at right around 14.7:1

[crzycav86]

My idle stays at around 10.8:1 with the ac off. I'm pretty sure it's the walbro fuel pump gives too much pressure at idle. With the ac on, it idles at about 14.0-14.7:1.

I haven't finished tuning for part/wo throttle... pending clutch break-in