Hi there, I have removed my secondary catalytic converter on my HR12DE UK model, and I instantly noticed improved fuel economy of about 10%, and here in the UK we have an emissions test on our yearly MOT test, which it still passes easily, running at like 20% of the legal limits for emissions. No ECU modifications and I've been running it like that for the nearly 4 years I have owned the car, including upgrading to a stainless manifold-back exhaust approximately 2 years ago. Hope this helps
