Originally Posted by XwChriswX

What he means by it not affecting performance is that adding a resonator won't Detract from your performance. Even though an HFC doesn't have as big a Cat Cell as a stock cat, it still does have something the gasses have to pass through. So some performance will be lost. Resonated or non-resonated test pipes have Nothing in the way to block the gasses. Free-er flow = more performance.