[Christ]

Intake streams apply the same fluid dynamics as exhaust streams, only smaller... the air hasn't been super heated, thus, has less volume (same or slightly less mass, less volume).

Anything after the TB is where you tune your intake for flow velocity. Here comes a problem, though. If the flow velocity is too high, it could create an influx wave as it passes the valve, increasing pressure at the valve's face, and restricting airflow. (in theory, I've never seen it in practice, but this is one of the reasons that swirl induction came into play on high-speed engines, not excluding the homogeneity (yes, that's a word) of the air and fuel mixture.), so once again, it's best to tune for slightly above median airflow, then tune the length for harmonics. Ideally, you'd want the 1st harmonic frequency (the strongest) to land exactly where your RPM range normally falls while driving (Harmonics only affect a very small range of RPM), which means a very long intake pipe. You can always suffice with the 3rd or 4th frequency, though, and still get a net decrease in pumping losses at whatever your tuned RPM is.

By tuning both the intake and exhaust as a system within each other, and not by themselves, you can optimize your engine for it's best efficiency in a given RPM range.

Remember, though. If you tune just the exhaust, your intake will be improper. If you tune just the intake, your exhaust will then be improper. If you tune one, then the other, they'll work together, but they won't work as well as they could. If you tune BOTH, TOGETHER, they become complimentary to each other.

Of course, if you tune anything and change your BSFC for the better, your gearing will now be incorrect for maximum efficiency, and your engine's overall displacement will be higher than necessary for the same amount of work. Go figure. I guess ya can't win 'em all, right?