A 5lb heavier and 8-10lb heavier flywheel could perform exactly the same depending on where the extra weight is placed. If the 5lb extra mass is at the outer edge, and the 8-10lb is dispersed from center to the edge it is possible for the lighter to store more energy. I'm guessing Toyota located the extra mass correctly and it was all that was needed. I'm sure someone will correct me if I'm wrong. <img border="0" alt="[Nerd]" title="" src="graemlins/nerd.gif" />