[tirebird]

Here is an answer from a Mobil 1 tech to the same question I asked of the company about a year ago.

"Mobil1 MX4T 10W40 and Mobil1 V-TWIN 20W50 motorcycle motor oils, Mobil1

15W50 Extended performance and Mobil1 5W40 diesel motor oils contains
the higher levels of zinc and phosphorous for your cams. The new energy

conserving motor oils do have reduced levels of zinc/phos however, they

typically do not have any adverse effects on cams unless you are
running
higher valve spring pressures. I would suggest you stick with the
product listed above if you are concerned about the phos/zinc issues."

-Matt