[panhandler62]

Longer connecting rods provide for a greater moment arm which results in greater tourqe. There is not a huge difference in mass (and that will probably be compensated for by the new pistons anyway) but like any lever system, you can use a short moment arm to gain velocity or a long moment arm to gain tourque. A connecting rod may not look much like a lever but that is exactly what it (in combination with the crank journel) is.

There is a set amount of energy released in any given engine. Making a mechanical change such as this does not change the net energy release, it changes how it is transfered from the reciprocating action to the rotational action.