Just to correct that last post, the STC upgrade of the AA5 still results in a (on paper) 150hp engine. To save the costs of having to amend the performance figures with a new series of flight tests the engine is derated to 150hp by reducing the red line, to I believe 2600rpm, down from 2750rpm. However you still get the full use of the extra HP for T/O and climb which is the main reason for doing the modification.