A few notes on balancing ( I balance a lot of industrial rotating components at work).
Amount of acceptable unbalance is determined by the spec you're balancing to (precision, etc.), the weight of the component, and the operating RPM of the component. The formula looks like this:
N=Gx(W/R)
Where N= the amount of unbalance, G= the spec you're balancing to, W= the weight of the component, and R= the operating RPM of the component.
A note on the "G"--these are specs used by industry. G1 is the tightest spec, and the one we use at work. It'll basically get you down to hundredths of a gram of unbalance.
So knowing that, we can make a few assumptions:
--The higher the RPM, the lower the unbalance spec goes.
--The higher the weight of the rotating component, the lower the spec goes.
We could also reverse that and say:
--A lesser amount of unbalance will enable the engine to safely reach a higher RPM, limited of course by the valvetrain, and the accessories (alternator, etc) that's a whole 'nother topic though.
--A lighter rotating assembly (crank, pistons, etc) will also allow higher rpm's.
So Dan, you are correct in a sense. The Tec spins higher, so should already be balanced more closely than a OHV rotating assembly. However, most manufacturers, in the pursuit of a better bottom line, only balance as good as they need to so that the engine does not self destruct due to inbalance. Having the crank balanced at a rebuild will almost always provide gains, however small they may be. Better balancing will also reduce fatigue on other components, such as bearings. Vibration is a bearing's worst enemy.
The fact that the Tec is an aluminum block does not really matter here. The crank and other rotating components are similar to all other engines.
Here's how things are usually done for an engine balance:
Balance the crank, then attach the flywheel, or flexplate for automatics and balance that.
Pistons can be weighed, and material removed to bring all the pistons as close to possible to the lightest piston.
Rods can also be weighed, and material removed as above.
Other things can be done too, like precision balancing of the accessories (alternator, water pump, ps pump etc). This will allow these accesories to spin at a higher rpm safely also.
As a side note, the mechanicals of the SHO engine can be safely run to over 9k rpm, some speculate even 11k. It is limited by the accessories.
