Choosing the Correct AFR

Hi.

If using dyno, you can see which lambda (AFR) target is best, but how can you tell without dyno? How to select correct lambda target?

There isn't a "best" AFR or, more correctly, lambda - each engine is going to have a unique fuelling curve.

As a rough rule, for best power/torque, you're probably looking around 13-13.5: for gasoline/petrol, or around 0.9 lambda. For turbo-charging, you're usually going to be looking a bit richer.

Hi Gord,

I understand that. I didn't specify my question exactlly, sory. I am wondering how will i know the difference, for example if changing lambda @2300rpm and full throttle from 0.88 to 0.87. Change is visable in dyno, but how can you tell if this change was better or worse from 0.88 without dyno? The difference probably isn't noticable that much while driving? If you know what i mean

About the only options you have are a stop watch, or an "ap'" that measures acc'n.

Doing back to back testing on the same piece of road, as close as possible to each other and under the same conditions will give a comparitive base to work from.

As has been mentioned some sort of repeatable measurement with known quantities such a stretch of road and a Draggy or some other sort of data Acq device with GPS and/or accelerometers integrated to contrast and compare would be the 'best' way. That said if you're chasing power numbers with a fuel delta of only .01 lambda I think you're going to be pretty disappointed with the veracity of your results.

The other way to get an idea on what lambda is better for getting more power is to log ignition timing and compare pulls on the same road. Let's say you have ignition timing of 18 degrees at 7000 RPM and 1 bar of boost using lambda 0.8. But if you'll change lambda to 0.75 and it will allow you to increase ignition timing to 20-21 degrees in the same map cell (and the rest of them) without knock - that's indication of making more power which should be noticeable by Draggy.