Hey Pros,
I had a friend installed a DC header and Nismo exhuast in factory pretty long ago. However, he felt that there isn't HP been gained. So h went for a HP test and came out result with less HP than the stock. Therefore he had to install "oil changer" and reformated ECU. After that, his Z gets 310HP. The question i wanna ask is that do we really have to reformate the ECU and install "oil changer" to get the real gain on after market header and exhuast? I have a Nismo SS header and ready to purchase Fuji Y & cat, but I am so worried of getting the same result as my friend. Hope there will be someone know about this problem and tell me about it. Thanks and best regarts to all.

PS:I am not native Amercian, so my english isn't that good to translate "oil changer" from my language. If there's a misunderstanding of my English, please correct me on the "oil changer". Thanks.