I have heard that longer rods mean more torque, something to do with acting as a longer lever. But I have also heard that longer rods are a must in high rpm (high hp) engines because they cause the piston to spend more time at TDC which allows more time for pressure to build up and act on the crown of the piston (time is very limited at high rpms). I have heard NASCAR teams talk about rod lengths in the 6.2"+ range, but most wont say the exact length. Increasing rod length does add to reciprocating mass which reduces an engine's rpm capabilities.