M10 specific, I'm guessing more race oriented as the run for a while before narrowing from 4 to 2. He recommends "running them free-flowing full 2.25" exhaust, header-back, for best results."
Someone more knowledgeable chime in, but I think that means optimized for higher RPM's, (i.e. racing)
Do I need these on a daily driver car, no. Still want them...