[Ryephile]

If the engine has variable cam phasing and/or lift [a big if], there's some work that can be done to improve torque across the board with cam phasing along with subtle tweaks to ignition timing and perhaps some fueling. There are five primary things an OEM engine calibrator balances; emissions, longevity, fuel economy, driveability, and torque, likely in that order of importance from most to least. In the aftermarket, most tuners flip that around to get the most torque and better driveability at the expense of primarily emissions and perhaps longevity [not quite as applicable for n/a engines on the second aspect].

All that said, an N/A engine ECU tune usually nets minimal power gains as they're pretty close to optimized from the factory. Of course there are exceptions, and YMMV.

Also, when you start changing hardware [header, ported cylinder head, cams, etc.] you change the efficiencies of the engine [usually VE] that may need a re-tune to get the most out of the new hardware. Some OEM ECU's however adapt very well and can get the engine running pretty close even with different hardware. It all depends on the particulars at that point.