AFR

[marT350T]

Just looking at my graphs from a pastrolling road day and I hope some could tell me if readings are ok.

At tick over mr car was 19 and at full chat it was just over 10.

[stevieturbo]

Can you post a graph ?

19.0:1 at tickover sounds far far too lean, and if it was that lean, it would be running like a dog.

And what numbers does "over 10" mean ? 10.1 ? 10.2 ? or 11, 12, 13 ?

[marT350T]

can't post a graph as I have no scanner but at max power it was 10.2

[BB-Q]

You're losing a lot of power running that rich. You should aim to have your AFR's at 12-12.5:1 at WOT. You'll be very pleasantly suprised at how much free power you'll make.

At idle you should be aiming for stoichometric- 14.7:1

At cruise you can head towards 16-17:1

Edited by BB-Q on Monday 15th October 20:06

[CanAm Dave]

Hi Martyn

That's too lean at idle and too rich at full power. I don't run that rich with my supercharged engine and that needs to be richer than a normally aspirated engine.

Regards Dave

[marT350T]

Sorry I should of said the AFR I metion is for my 1.8 20v turbo polo.

Does all of the above still apply ?

[BB-Q]

marT350T said:

Sorry I should of said the AFR I metion is for my 1.8 20v turbo polo.

Does all of the above still apply ?

Yeah, I knew what car we were talking about!

[stevieturbo]

Still too rich.

Aim for mid 11's at WOT.

[BB-Q]

stevieturbo said:

Still too rich.

Aim for mid 11's at WOT.

I disagree- all the dyno evidence I've seen shows that a turbo motor likes it best @ around 12.5:1. You'll still lose power @11:1

[stevieturbo]

It will lose a minimal amount of power.

Theory does state, that 12.5 or maybe slightly higher can be better for power.


but unless you were monitoring AFR's and EGT's on an individual cylinder basis to ensure each cylinder was exactly where you wanted it, I would never consider running 12.5:1

I dont know too many other fast runners, that would tune their cars to 12.5:1 either.

[ringram]

19:1 at idle is too lean if its true, but consider that you may have an air leak, or your wideband is Ill, or you have done mods to the engine like cam, intake etc which means its not fueling it enough in open loop.
It depends on how your ECM works? Do you know if idle is open loop or closed loop? Whats the commanded fueling at idle? How does it determine airflow? MAF, Speed Density or basic TPS? etc, etc.
So you know the symptom, but not the cause

[marT350T]

ringram said:

19:1 at idle is too lean if its true, but consider that you may have an air leak, or your wideband is Ill, or you have done mods to the engine like cam, intake etc which means its not fueling it enough in open loop.
It depends on how your ECM works? Do you know if idle is open loop or closed loop? Whats the commanded fueling at idle? How does it determine airflow? MAF, Speed Density or basic TPS? etc, etc.
So you know the symptom, but not the cause

All the mods you mention have been done to the engine.
Sorry but I havent got a clue if my idle is open or closed loop how can I tell ?