I'll provide some thoughts on the mods and results below. As usual, each dyno sheet is showing runs from the same day with equivalent coolant, oil, and intake temperatures. This will provide true before and after results.
Step 1 - Headers, Off-Road Pipes, and Plugs:
The dyno sheet below shows some VERY interesting results from my Kooks header installation... no power gains! This was a bit disapointing at first, but simply proves that the factory manifolds and catalytic converters provide sufficient flow for ~600rwhp. This behavior is not uncommon on supercharged vehicles; we see it with Mustang Cobras and GT500s too. Blown motors do not experience the same benefits from improved exhaust scavenging as naturally aspirated vehicles because the supercharger is pushing the air through the motor. The exhaust simply needs to provide a hole big enough to let the air out.