[Boofneenee]

A catless header without a tune is not healthy for the engine. You are realling leaning things out which increases temperatures and increases chances of knock. You can get one and avoid tuning because you want to avoid voiding your warranty or you can do what is healthy for the engine. Not to mention your car will run like shit without a tune and headers. Your choice.

BRZ their are plenty logs out there for you to review if you want to educate yourself. The best approach is to compare a solid, quality tune to one with no tune and only headers. Compare the afr's and other variables.