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Thats a good question.
I tried to find a good explanation that I could just copy and paste, but none of them really explained what was going on.
The cams duration, lobe centerline, and lobe phasing (advanced/retarded) all work together to determine a number of things. Among them is the cylinder pressure, or cranking pressure (compression), and RPM range of the motor.
There are number of ways that you can acheive your desired results, whether its high RPM power, or MPG.
Altering the phasing will alter the point relative to crank rotation, (piston position) and increase (advanced), or decrease (retarded) cylinder pressure, and to a similar degree, RPM range, with advancing the cam dropping the RPM band
If you want to consider a cam to be advanced, or retarded, you need first to have a baseline from which to start.
The Metro is timed really late, at 114.
Most street cars are around 110, with most performance cams being setup near 106.
A nimber of Porsches are setup as low 98.
So what is advanced, and what is retarded? Good question.
You have to look at what you have now, what you want to acheive, and how you can do it with what you've got.
The small motor in a big car scenario will always favour less duration, with a lower intake caenterline (advanced).
Since you can achieve similar results by tweaking the individual parameters, you may learn from experience what works beast. In my race motors, I like to run a little too much duration, then pull it back down a bit by running a lower intake centerline. It seems to give the bottom end grunt that I like.
Consider cam phasing as a tuning tool.
For the street metro, wanting MPG, you would think a little less duration, and a little tighter centerline would be about right.
With a typical centerline being around 110, I would think that with a short duration cam, and stock compression, 106-110 would likely give a pretty strong bottom end, and good efficiency in the cruising range.
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I`d be greatfull if you could e-mail me those 4 grinds timimgs and valve lifting on PM or post them here, as not only me may be looking for your cams 
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