[The Radium King]

variocam+ would account for some of the hp on the table vs the cayman.

but if we are not comparing to caymans but rather looking at 10:1 afrs using stock tune, then why? if the maf was consistently over-metering the air (resulting in more fuel than required) then the o2 sensors would pick up on it and adjust the fuel trims. similarily if you had leaky injectors or an over-performing fuel pump producing more fuel than expected then the 02 sensors would notice and adjust trims.

so, perhaps new o2 sensors? a quick trip to auto atlanta shows that the 986 02 sensor has a different part number that the 996; most likely due to lead length, but perhaps they are different beasts in other ways?

otherwise, the ecu will add more fuel to keep the heads cool if it is nervous about something - timing, octane, etc. - what gas are you running and is it a row or na 996 tune?