Discussion and questions related to the course Understanding AFR
if a lean afr makes for less torque, does a fat afr give better torque? maybe something like a .90 or .95 lambda would give better torque than what the oem typically uses?
A dyno will allow you to conduct this experiment. Not every engine is the same. USUALLY .088 - 0.90 Lambda will produce the peak power, but I've seen some engines that make more power with 0.92 Lambda and a different ignition timing.
Here is a common picture used to show this:
As David said, different engines will respond differently - the better the fuel-air mixing, the closer to stoich' it will usually be. For example, some older, especially V8, engines have poor air distribution between cylinders, some carburettors have poor atomisation, some combustion chamber designs have poor turblence, etc - all these things will affect the specific fuel mixing and sometimes a compromise has to be made.
Also, as David said, you may find adding, or subtracting, a little fuel and adjusting the ignition timing may give better results than using a specific xxx:1 AFR for all applications.
OEM mapping has to take into account many things, not least emissions like CO, so there is a good chance you can make a small gain in torque/power by enriching the fuelling a little, but it is by no means guaranteed as some engine managements will just pull fuel to correct it back.
Thanks everyone, I suspect that VW left a little torque in favor of emissions. Since the 2.5l 5 cylinder was their last non turbo engine used in their cars. But their computer systems in 2011 were pretty good. Probably won't get a lot of torque by richening up the mixture but it will be interesting to find out.