Air Fuel Ratios

I have seen so many posts on AFR, but sadly I’m not sure which way it goes or what is dangerous?
So is 11 lean or rich? and what is the suggest max in each direction?

11 is rich

14.7 is Lambda 1 and rich and lean is based around that figure. The lower the number, the richer the mixture.

There is no hard and fast number for what is right and what is wrong. At part throttle cruising you would want to see about 14.5, which would make a nice fuel efficient cruiser. However at full hammer my turbo charged car goes down to 11 at high revs, as it just needs loads of fuel.

If it is an NA car, at full chat I wouldn’t want to see higher than 13.5. But I am no expert, so don’t take my advice. lol

Thanks Sean that is a load more than I knew before your post so I get a good idea what is good or bad

Hi Ade when mapping the sc honda we didnt want an afr of less than 11.5. It starts at aropund 14 and drops there as you rise through the revs. Are you using a wideband to monitor it? Also have you got your ecu back yet? Im desperate to hear about the results!!

I have no monitor at the moment but I now plan on installing one, my ECU is not back yet as soon as I have more information I will post it

I’ve been having the same dilemma with my camper van. I bought an Innovate LC1 which I was going to plug into the DTA S60 ECU but it appears that the Innovate is a bit pants. It appears to be reading too rich at higher power outputs compared with the ETAS system which is on the dyno so I’m binning the LC1. Instead I’m getting an NGK AFX system from Apparently they are very robust and accurate.

Badnis, I’ve had the NGK in my car from the start, good choise…

The 2ZZ runs it’s best with a 12.5/1 A/F for power…

Thanks for the advice guys


Is there a UK supplier of these or did you import it?


I’m getting mine from my engine builder John Maher Racing. He’s got 2 on order at the moment but I’d imagine it would be much easier to just import one.