For various reasons (wanting a reliable solution with a very OEM look, maintaining cats in both stock locations for emissions, and a wife-friendly sound), I had narrowed my choices down to staying NA with an HKS catted header, doing an FA24 block swap (if possible - I'm watching
Opie's swap thread closely to see how it goes), or supercharging with either the HKS GT2 or Harrop kits (probably in conjunction with the HKS catted header).
So, I nerded out a bit (OK - a LOT) on torque curves with the various different power-adding options, spending lots of time looking at posted dynos from different sources to map out as best I can the comparative curves in one Excel spreadsheet and charting them visually vs the lone dyno I have of my Tiburon (which was before I spent 2-3 years tweaking the tune on it almost daily which greatly improved the top-end power, so I took those dyno numbers and guesstimated the values from 5500 rpm up).
I also added in the ACE A350 header, since that was what my original plan for the car was before I bought it and I wanted to see where that or the similar JDL EL 4-2-1 with over-pipe would fall, and I also estimated numbers for a 2.4L block swap by adding 10% to the FA20 numbers. I also did the same with the FA20/HKS Header numbers to get an idea of where they'd be as well with the extra displacement.
Why not use an actual FA24 dyno plot, and why only 10% for a 20% bump in displacement? The curve won't be the same as an FA24 due to retaining the FA20 heads, cams, intake and exhaust manifolds, etc. It also won't simply be 20% more due to the 20% displacement bump since the heads and pistons won't be "optimized" for each other like a factory setup, which is particularly a sensitive point with direct injection, so I'm being pessimistic with the projections. I would hope the gains would be closer to double what I've plotted and that the torque dip wouldn't be as severe, but I'm looking at worst-case (other than the swap not working at all). I also just couldn't find a dyno for a 2022 BRZ/GR86 from a Dynojet and tuner whose results I would trust.
Finally, I also took into account the weight of the vehicle with each option (including adding 75 pounds for the HKS GT2 kit, 125 pounds for the Harrop kit, and 150 pounds for the Tiburon), and also plotted them out vs. the gearing differences between the Tiburon and the BRZ in 3rd and 6th gears.
Up next are the charts, and my thoughts on each of them.