Momentum's affect on torque.
 

This issue concerns lightening the rotating assembly of an engine to increase horsepower (primarily by allowing it to spin to a higher rpm).
Now, ignoring momentum it seems obvious that having the same explosion in a cylinder forcing a 300 gram connecting rod vs. a 600 gram connecting rod that the 300 gram connecting rod would yield a more forceful explosion and thus more torque at the same rpm. But, does the momentum lost by going to the lighter connecting rod have a negative affect on torque?

off the top of my head, im going to go with no. when dealing with a rotating assembly (especially rods and pistons) all of that mass must come to a complete stop (@ TDC) then accelerate back down, in other words the rods and pistons lose all of their momentum at TDC no matter how much they weigh. The lighter the components, the easier it will be to accelerate and decelerate