"I agree that reducing reciprocating weight is beneficial for horsepower. However, there are a lot of more important things that take precedence over the budget."

You could have used the early rods which are lighter & stronger than M rods for no extra cost.

"Question, because I really don't know: Why do late B20s have more reciprocating weight than early ones? Where is it?"

They have B21 rods in them with the heavier style piston.

"Why would more mass bend a properly balanced crank sitting if properly aligned bearings? I don't see the dynamics of this, unless harmonics enter the picture."

Inline 4's are never really balanced unless they have a balance shaft or two in them, it just natural that they are rough. When you balance the crank, it is balanced alone with disregard to what the pistons & rods weigh. The heavy the pistons & rods are, the more they jump up & down as there is nothing to counter them like there is in 6's & 8's.

"As for heads, ports don't need to be all that big to take advantage of higher displacement. It's more a matter of combustion efficiency -- how much energy you get from a charge of air/fuel -- than of sustained flow. The quality of the burn is just as/more important than the quantity. That being said, with a well-matched cam and header/exhaust and some resonance tuning of the intake, you can get excellent VE without huge ports."

Port velocity determines what is possible. Port velocity is controled by how big the ports are compared to the capacity. It's hard to get power out of a B20E head under 2000rpm purely because the port velocity is too low. Equally hard above 6000rpm because the velocity becomes too high. Making the engine bigger just moves the possible powerband downwards.

"I'm running 93mm pistons, heavy "M" rods, big heavy valves, a B20F head with ports that still match the OE manifold gasket (although they have been reworked considerably for shape), and I can tell you it goes just fine, tolerates 7000 rpm no problem, and gets better gas mileage than a stock B20 when driven at similar performance levels."

Yes, but it is full of comprimises. If you closed the LCA of your cam up to 100 & change the headers to 4-1 you would end up with an engine that develops more power at less revs.

Cheers,
Paul.