Mixture adjustment on the fly

[Justinp551]

So I have been thinking of enabling a small "controlled leak" around the AFM in my L28E when freeway cruising. My thought is the AFM door would have less air opening it which would tell the computers to inject less fuel. Hence on a low load on the engine it would be in super lean cruise mode. We operate aircraft engines to lean of peak egt temps when in cruise flight. Why not a car? Now I have done a bit of research on here and have come across some high egt numbers for turbo applications which should never be seen in a NA application so I am not worried about burning anything up. Also planning on installing a egt gauge and wideband to keep a eye on things. I came across some info on Atlantic z techt board that the AFM gives a voltage to the ecu depending on airflow. Instead of a "adjustable leak" around the AFM could a adjustable resistor be placed somewhere between the computer and pins 6-9 of the AFM to lean the mixture out in 5th gear during cruise conditions? Looking forward to the input.

[Tony D]

It will only work below 30% throttle opening, and around 3000 rpms.

 

Anything more and you are on pre-programmed fueling curve equating to WOT.

 

Using a Megasquirt with a WBO2 having adjustable narrow-band output to allow correction to 17 or 18:1 AFR during low load conditions would be a bit more reliable and FAR more tuneable than playing around with 2nd Generation Bosch AFC Licensed 70's technology! (Or using more advanced AFR-Target Software for the MS, simply program direct AFR's for the cruise conditions.)

 

Pulling fuel past peak torque is something few people ever do on the L-Engine, but it's what you need to do to get that last little bit of HP, and it doesn't affect EGT much at all. Under low load, it's not uncommon to run at 17, or 18:1 without any issues whatsoever. You can go leaner, but you want to start integrating EGR to the equation for best performance.

[Leon]

Under low load, it's not uncommon to run at 17, or 18:1 without any issues whatsoever. You can go leaner, but you want to start integrating EGR to the equation for best performance.

I'm not understanding the basis of this statement. Do you suggest that you need/want EGR in order to have best performance at a leaner mixture?

 

To the contrary, the more EGR you introduce into the cylinder, the less tolerant the engine will be of lean running. EGR not only increases burn duration (this is why spark timing must be advanced with EGR) but also has a diluting effect, similar to leaning out the mixture. This has a destabilizing effect on combustion. Really, the leaner you go, the less EGR you want (or need!). NO_x emissions drop off after they peak slightly lean of stoichiometric.