They are talking
About to the shaving left inside the manifold after poor machining I think? And would end up getting sucked into the engine. From what I see is the knock off takes some machining and smoothing out to get it ready ti bolt on. Hence why it's cheaper.
i think it will make the d23 behave a little more like the svt engine by shifting the powerband UP. what i find disappointing in the duratec is the top end at freeway speeds. these manifolds would pep that up. many look at the peak gain and say its not worth it, but if you are craving an engine that pulls hard up top for better hi speed acceleration, this is what you need. everyone knows the d23 in stock form is very torquey in the midrange, but the hp up top dont cut it. your engine WILL lose some low end torque, but overall acceleration will improve because of the newfound top end power. even if it is only 7 to 10 hp