Also for reference in this thread (from the TCI website)>
TCI 727 and "Streetfighter" convertor = 171lbs
TCI 904 and "Streetfighter" convertor = 140lbs
31 lbs difference, the majority of which is internal rotating mass. Not a whole lot of difference in the weights of the bare aluminum cases.
A good example of "parasitic" loss is the common belt driven water pump. Not counting the fan, a pulley driven water pump takes about 6 fwhp to operate and as we know it can easily be turned on a motor with one finger and it's probably a pound or less total in rotating mass with the pulley and impeller. You can than do the math what 20-25 extra lbs of rotating mass can do to your RWHP.