Flyinkiwi... My whole point is that the MAP can NOT be relied upon as an indicator of power.
Lets say that we loose one magneto during T/O roll. The MAP would still indicate ambient pressure (if full Throttle and normal aspirated) and we would still have max rpm. But we would have less power and the prop would be in a finer pitch in order to maintain rpm. We would notice the power drop only when power has decreased to the value where rpm goes in full fine and not able to maintain rpm. Remember that MAP shows about 30" even with engine stopped!