[oil pan 4]

There was some one on here years ago that had a DOHC engine and tried retarding the exhaust cam all by its self in one test. If I remember correctly it made almost no measureable difference.

If you have a single over head cam you are more closely related to an old school in block cam push rod engine then you think.
Since the beginning of gasoline engines people have advanced the cam timing to increase fuel economy and low end response and torque of a daily driver car. But advancing the cam makes it harder for the engine to breath on the big end.
Retarding the cam is good for high speed, high horsepower and at the expense of low end performance. Retarding the cam may provide a fuel economy improvement only on the high RPM end of things as far as I can see.
As far as I know the only people I know of who run retarded cam timing don't care about fuel economy (drag race engines and circle track racers) or the people who don't understand engines read something to the effect of "retarding the cam timing will produce more horsepower" and put any and all considerations aside and go for it.

I advanced the cam timing one tooth on my Toyota 1.8L DOHC that I had when I lived in japan when I was replacing the timing belt. I wanted more low end response since japan was all city driving and the highest speed limit in the country is about 50mph.
It worked for that reason, but I was not measuring fuel economy at the time. So I don't know what effect it had there.