23rd Sep 2005, 17:36

Inorder to improve engine efficiency, reciprocating and rotational mass should be reduced as much as possible, but not reduced below a design factor of 3 (street performance). Reducing reciprocating mass (ie:pistons, rods) will allow the engine to be balanced with less "counter-weight" on the crank shaft and will inflict less stress on the crank shaft, bearings, main caps, block, and cylinder walls. Friction generated between the piston and cylinder walls also prohibits efficiency.

With gas prices rising and the consumer demand for high Hp V8's, automotive engineers are producing more efficent engines, but there are compromises. GM's 5.3L & 4.8L LS1 based, V8 engines are full of compromises. The pistons have low tension rings, and reduced overall height. The pistons have a smaller contact area with the cylinder wall due to their reduced height, consequently reducing friction. However, if piston/wall clearance isn't correct, piston slap will occur easier due to the reduced height of the piston. The LS1 has tigher tolerances than any mass produced V8 in GM's passed. Catastrophic engine failure at 40,000 miles because of the sympathetic piston vibration, which occurs at low engine speeds (1000 to 1175rpm) in LS1 engines, is impossible. The accumulated time the engine spends in this speed range, where "piston slap" can occur, would not cause excessive wear. Over long periods of time, cyclic stress from piston slap, will cause a piston skirt to break off. Piston skirt failure is most common in 2-cycle engines with aluminum pistons (ie: boat engines). The high rpm's of a 2-cycle (4000 to 7000rpm) accelerate cyclic stress.