Although the 1m engine is a bit underrated, it is not as underrated as many like to think. Anyone who has played around with 1m's vs m3's on the streets in rolling races, will know that the m3 consistently pulls away at any speed or any roll start in a linear fashion in the way a car with about 30-40hp more horsepower would.
But you need to take into account the weight and the 1m weighs 400 pounds less which is roughly a 40hp equivelent advantage to the 1m
So for equivelence the 1m's 330hp plus 40hp gives it 370 hp equivelent hp compared to an m3.
370 is about 40 hp less and exactly how much hp is needed for a car to pull away like the m3 does on the 1m.
So while maybe underrated, it probably is within a variance of a true 330 to 350 crank at the most.
Dyno turbo cars have such drastic variance compared to a NA motor you can't compare the two