Simply stated, the better the balance, the more the potential power that can be seen at the flywheel. For the driver of a vehicle with a balanced engine, it's a physically smoother running engine with improved acceleration.
Engine "balance" deals with the physics of achieving a rotating mass that is the most conducive to transmitting as much potential power as possible to an engines flywheel rather than having it wasted within the confines of the block. By eliminating power robbing vibration or harmonics that can be caused by a state of out of balance, power or torque that would normally be dissipated through an engines main bearings and into the block can instead be redirected to the drive end of the crankshaft proportionally by the degree to which the rotating mass is balanced.
The connecting rod plays a vital role in the engine. But a connecting rod is under tremendous stress, with the weight of the piston sitting on top, changing direction thousands of times per minute. This continuous stopping and changing of direction combined with the weight of the piston and speed of the engine hammer on the bearings and torture the rod bolts which hold everything together.
Proper geometrical alignment and bearing surfaces that are smooth and perfectly round is the best way to ensure long engine life and happy customers. Any unwanted lobing, chatter or misalignment, particularly in engines that operate at high rpms, will affect the engine's efficiency.
In the racing world a sonic tester is used to measure the thickness of metal in areas that canít be accessed for direct measurement, the most common being cylinder walls and roll bar tubing.
Just like a bat or a radar gun, the sonic tester sends out a sound wave and then calculates the thickness of the metal by measuring the time for the reflected wave to return.
There are two ways to get it wrong. The first is usually catastrophic: If you have insufficient clearance, the pistons hit the valves, followed by the predictable parts damage. On the other hand, if you have too much clearance, the engine will run, but it won't achieve anything close to its performance potential.
You must have the knowledge and tools to get valve to piston clearances set optimally.