Thank you for all of this, Rob. REALLY grateful to have you as a contributor to this forum.
This, specifically has the potential to change the economics of running our gas guzzlers significantly. But it seems we're in our infancy of understanding it well enough as DIYers to make it happen reliably without messing something expensive up. There would likely be a big market out there for a reliable lean burn "kit" for these trucks.
Back in the mid 90s there was a group of pilots and engineers out of Oklahoma
who figured out that running aircraft piston engines lean not only worked well, it had huge benefits to engine cleanliness and longevity. Conventional wisdom to that point had been that you needed to run them rich because the extra fuel would help cool the valves, etc etc. But those guys proved that that was totally false.
They figured it out by using some new (at the time) technology to directly measure internal cylinder pressures throughout the combustion event in a Continental aircraft engine (8.6:1 compression ratio, so detonation wasn't as much of a risk as it is on our engines) on a test stand.
Background information needed: In aircraft piston engines, pilots use exhaust gas temperature (EGT) to determine the optimal mixture setting because it must be periodically adjusted as the aircraft climbs and the air gets thinner. As the pilot adjusts the mixture they look for the EGT to peak (around 1500ºF) and then adjust the mixture accordingly. Well, conventional wisdom had pilots running the mixture at around 50ºF rich of peak (ROP). Turns out that that's very close to where the peak internal cylinder pressures occurred in the test stand engine. Laws of thermodynamics say that more pressure = more heat. So, not only were pilots burning more fuel than necessary, they were actually putting more heat into the cylinders, valves, etc leading to higher failure rates because these engines are air-cooled. Failure in an aircraft engine can have some undesirable consequences. So, instead running them around 100ºF lean of peak EGT kept them running much cooler, on much less fuel, with only a very small penalty in power output.
It gets better. What they also learned is that the engineers back at Pratt & Whitney in the 1920s and 30s knew this already and large piston-engined aircraft like the DC-6 and Lockheed Constellation used lean-of-peak (LOP) operation to make transoceanic flights possible. But that knowledge had been mostly lost by the 1990's.
Anyway, all of this is to say that running a piston engine lean for better fuel economy has a long and glorious history. I don't know why car companies don't do it more today but my guess is it has something to do with the inherent conflicts between fuel economy and emissions regulations in the US and EU. The Aussies apparently took a more pragmatic approach.
