The engine runs lean with hfc and test pipes?
If you want your car louder, why not just get electric cutouts for adjustable sound? Add one after the last metered cat and before any resonators or mufflers.
isnt taking out your cats illegal??
No, it's still illegal even if you're not caught yet.
BUT I also wanted more hp or better acceleration
I can't talk for hfc but for test pipes man I felt the kick in the car when I pushed it. Few other members here on he scene from ny test drove my car and they can feel the difference but be prepared for it to be so loud. I've been driving like that for 2 years no problems with the cops but I got tired of the noise and mostly people complaining in my neighborhood. But performance wise it's worth to get test pipes in my opinion.