Complex sentence: The Spey gave an increase of 10% in operational range, 15% increase in ferry range and better low-level acceleration, however the increased drag of the engine installation resulted in poorer performance at high altitude.
Split into simpler sentences: The Spey gave an increase of 10% in operational range, 15% increase in ferry range and better low-level acceleration figures. The increased drag of the engine installation resulted in poorer performance at high altitude.