I came across this post while searching for the ideal AFR values for a tuned IX on 93 octane:Is that accurate? 11.5 until 6000rpm, then declining to 11 or 10.5 at redline?

My wideband is on its way, just want to know what I'm up against. Thanks, in advance.

 

Ideal AFR's will vary widely depending what area of the map that your car is in at the given moment. Cruise, idle, low boost and high boost should all have different target AFRS. It is not as simple as justing shooting for 11.5 across the board.

 

Optimal power is more like 12.5 but folks feel that is too dangerous for our turbo'd cars and recommend 11.5 for WOT, high load, or high rpm runs....It will vary based upon your timing and boost and you may need to run even richer, but 11.5 seems to be a general guideline.

 

So what's good for idle? 14.5 ?
Cruise? 12.5 ?
Low boost? 11.5 ?
High boost? 11.0 ?

 

Forget the idle can't change that, most tuners will aim for 11.2 WOT.

 

Of course you can tune the idle. What do you base such a statement on?

 

Idle - 14.7:1
Cruise - 14.7:1

In closed loop mode (when your car is warmed up and not at wide open throttle) the ECM reads O2 sensor voltage and adjusts for a target 14.7:1 AFR.

When you let off the throttle under low loads you'll see the AFR go totally lean, which is for emissions. Doesn't hurt anything.

Low boost or high boost.. there are all types of schools of thought that depend on how much boost and what type of fuel you're running. A lot of tuners lean things out at spool up because a "lean" spool is believed to be faster. On pump gas most tuners aim for 11.5:1 which is a relatively conservative number that still yields good power. With meth or race gas you can go leaner.

Target AFR in open loop (wide open throttle, when the computer is reading from tables rather than monitoring live O2 sensor voltage) depends on what load cell you're in at a given RPM. Generally speaking, the higher the load cell the more fuel you'll need. But how much timing and boost you're running at a given point matter a lot, too. That's why a good tuner is able to look at things like load, boost, timing, knock counts, EGT, and AFRs and come up with suitable fuel and timing maps.

 

i think injector size also determins afr at idell.

 

There is no answer, because AFRs are only one piece of the tuning puzzle. You don't try to tune your AFRs for idle or cruising, because the ECU handles that in closed loop mode by shooting for 14.7 as already mentioned. The high-throttle map will be made for high boost and 11.xx AFRs, but where those AFRs fall will depend on timing, boost, octane, altitude, and load.

 

What he said.^^^^

EvoTech if you have a way to change AFR's at idle please enlighten us.

 

afr depend on too many things to just pick an ideal one, with the cars i tune in most cases they wind up around 11.8-11.4 tapering down to 11.4-11.0 but it really varies a lot...

 

Not everyone uses the stock ECU. AEMs and other standalones allow you run whatever you want for idle and cruise. Alternatively, you could use the narrowband output from WBO2s that have this option and are adjustable if you remain on a stock type ECU.

 

Also, you can simply flash your stock ECU to run in open loop at all times. Then you would have complete control over AFRs, even at idle.

I'm not suggesting that you do this, but this is one way.


Eric

 

11:5 steady for WOT on pump is ideal ... 12:1 steady on race is good ..both will keep you safe ..get water injection and you will have additional buffer ..