The P2 cars in ALMS can't really compete with P1.
The ACO clearly states that a 1,5% time gap will be enforced (with required modifications at the end of the year if not upheald) between P1 and P2 classes. Although IMSA hold the right to implement their own performance equalizing, up till now they have only implemented performance equalizing rules for cars within the same class. The IMSA regulations however, state that if there are no IMSA specific rules passed, then the ACO rules apply. The ACO rules are the basis for all "Le Mans" type championships.
Given the above, I'm interesated to see what happens if the P2 cars give the Audi's a hard time. (not likely...but on tight tracks, you never know)