Engine Balanced vs. Stock Engine

[Progression]

For those that have had their engines balanced when rebuilding/building them, what precisely are the differences between the balanced engine and a stock engine? In other words, lets take two cars, one with engine balanced, one without, exact same mods, exact same internals, and describe what it is that is different between one and the other.

[turbojohnny]

having your rotating assembly fully balanced will have a few advantages. it will help the longevity of the bearings. the engine will rev more smoothly and it will also accelerate more smoothly and maybe not noticeably but it will accelerate a little quicker.

[Progression]

So when you say it will rev smoother, you are saying that it will feel more linear or even more like a naturally aspirated car. Is this correct?

Reason I posted the OP is because I am considering just dropping in forged pistons OR completed my bare shortblock with the rotating assembly and clutch/fly/balancer/etc. all balanced together. Forged pistons would be price of gaskets is all since I can do that, but doing the completed shortblock including balancing then involves all new parts and also the machinist getting things in spec.

[mike saunders]

You can weight balance your pistons and rods yourself to better than OEM tolerances if you have an accurate scale and a steady hand with a grinding wheel.

For crazy pants power, though, you'll want to have the entire rotating assembly balanced and probably knife edged to better match the reduced weight of the forged pistons.

[Progression]

Very good points Mike. Reason I want to go forged is the obvious reasons) I didn't think about it, but it makes sense since the block is already off the head to just weight match rods+pistons...wouldn't be crank-rods-pistons-harnomic balancer-fly-clutch, but at least it would be something. I wanted to use the B234 parts, but I don't know how to compensate for that low compression other than what some UK people said to do (skim the head enough bring compression up using B234 head gasket).

[Drew in Houston]

Got your PM too. Here's my take in addition to what the other guys wrote: A balanced engine can run higher rpms and should last longer, plus they're nicer to drive all around. Less vibration, smoother feel...that sort of thing. In industry, one of the major predictive tools that rotating machinery specialists/engineers use to determine equipment health is vibration monitoring. It's a relative scale where less vibration is better than more, but at the far side, things can and do actually fly apart when the balance gets bad enough. An increase in vibration and seismic activity is a precursor to failure typically, and the lower you can start initially, the longer things last.