How do you know if an engine is running rich / lean ?

[Rob Clark]

I'm curious to know how tuners have played with ait intakes etc and have said because of the increased airflow the engine runs lean and the car was remapped to allow more fuelling ?

How do you know. I can guess that via the combination of sensors the 'burn' will be ideal and have littel waste ot 'dirty' and the sensors (can only gues lamda on exhaust) can detect a change ?

Discuss pls

 

[stan*]

Typically you use a wide-band lambda sensor which gives real-time exhaust gas composition changes, and so set fueling that way, as obviously oxygen content changes as a function of fuel input.

You can also use exhaust gas temperature as an indicator of efficiency of burn, but this is also influenced by ignition timing, so this is always used on a rolling road for e.g, but maybe on an engine dyno where its being calibrated to the Nth degree.

 

[Rob Clark]

so the lamda will show certain conditions for optimal, lean and rich mixtures which can then be tweaked via altering timing and/or mixture

 

[cat171]

Look at the exhaust, if it's running rich the end of it will be sooty.

 

[stan*]

well...if your mapping a car on the rolling road, sticking your head out the back to take a visual on exhaust gas isnt really going to get you far!

typically an engine will require an air-fuel-ratio of around 13:1 to give optimum torque, so thats your target when mapping at full load. then under cruise areas, you may go for 15:1 to bring back a bit of fuel economy.

 

[Dan@SJM]

is that optimum torque and power? or just torque, stoich is 14.7:1 isnt it?

 

[stan*]

optimum torque GIVES optimum power, since power=torquexspeed.

yes, stoichiometric is 14.7 (lambda=1). Though you can go leaner than this for cruising/part throttle.

 

[Dan@SJM]

I did think it equalled both.

EDIT: I rmember what i was taught in college now about stoich, that its the ideal burn, not for optimum power

 

[bmh.01]

Stoich is your perfect chemical burn I think, but in the real world its not what you go for.

 

[stan*]

its a theoretical value for complete burn..in reality its never achieved.

like i said earlier, depending on what condition the engine is running at determines what AFR you aim for.