That's the tricky part.
I use my wideband O2 controller (JAW) and bosch WBO2 sensor to actively monitor. My caravan's 2.2L like to slurp gas too easily because I'm not finished with tuning the carb and need to order more jets. When I accelerate, I have to keep easy on gas or else I hit 14.7:1 and richer too easily.
(Weber jets I need to get: idle jet of 47.5 and 45), fuel jet: 127.5 and 125.)
I'm currently on 130 fuel and is too rich at low end of rpm (around the max torque 2.2's is 3200) just after throttle is past transition slot.
I did see that mythbuster's episode on drafting behind trailers, up to 80% less on fuel consumpation is seen.
Cheers, Wizard
