Into the weeds engine design for fuel efficiency discussion.

So back in 79-81 I drove a Datsun 1200 sport coupe. I LOVED the car and wish I had never sold it. Anyways, I used to carry a timing light and tools with me and would advance the timing on foggy or humid days and I got phenomenal mileage. I would then have to retard the timing on dryer days as I heard the knock or pinging. Interesting how variable timing does just that these days.