Continuing my fuel economy sermon ...
Let me emphasize -- Driving style is usually the single most significant factor affecting fuel economy.
Case in point: My '77 Dodge B200 van, with a 318 engine, averaged 18 mpg during typical driving and load, if I kept it down to 50-60 mph. This was in the mountainous area around Anchorage, Alaska, including frequent trips over Turnagain Pass. It probably would have gotten 20 mpg or better in the Midwest flatlands.
I often drove at 70 mph or more. So, actual average fuel mileage was 14-16 mpg. It would have been even worse but my acceleration and brake usage favored better mileage.
Yes, the engine was tuned for good (not maximum) fuel economy, to match my driving style and use.
My '69/70 Explorer Class A motorhome got 14-16 mpg, if I behaved myself. Usually, I got 10-12 mpg and it dropped into the single digits if I was in a hurry.
The speedometer was broken so I never knew just how fast I was going. A friend once followed me from Anchorage to Homer, Alaska. When asked how fast I was going, he said, "Well, you occasionally slowed down to 65." (He also mentioned I tended to ignore lane markings ... I replied, "The state laid down all that pavement so I might as well make full use of it.")
The old timer I quoted in my previous post taught me to "tune by ear." I now use a timing light for initial timing but tweak it by ear afterwards. Process is rotate distributor back and forth a bit until I find fastest idle RPM, adjust idle back down to 550-650 RPM, and repeat until I find the 'sweet' spot.
It's worth noting I once used this technique to tune two identical OEM engines. When I was done, the timing light indicated two degrees difference between the engines. Both had a roughly equal improvement in fuel mileage. (One of the owners complained he suffered a 2 MPG decrease in fuel economy when a shop re-tuned his engine to factory specifications.)
The 318 engines in both the '77 van and '69/70 motorhome had advanced timing (more degrees BTDC) than factory specifications. This produces earlier ignition, leading to a more complete burn and more power out of a given fuel-air charge.
However, doing this requires a light foot on the accelerator to avoid engine ping and knock. Advancing the timing too far can result in the expanding combustion pushing piston and connecting rod against the crankshaft rotation. In extreme cases, this can lead to engine damage.
While my experience is limited to the two 318 engines and non-Mopar engines, I believe advancing the timing in all non-computer-controlled engines can improve fuel economy ... provided you don't go heavy on the accelerator.
Process is to advance the timing a few degrees, until the engine starts knocking or pinging during normal driving. Then back off (******) the timing a few degrees. (Going up a steep hill is the best indication you've advanced the timing too far.) Be careful, a few degrees at a time to ensure you don't damage the engine.
Next up is other inexpensive things you can do improve engine efficiency.
Addendum after posting: RV.NET's nanny routines 'starred out' the standard term I used for the opposite of advancing the timing. This is because it is also a derogatory term for people suffering diminished mental capacity and/or learning disadvantage/disabilities. (i.e., "advance the timing" versus "****** the timing.")
