Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Most restrictive part of exhaust system?

the heads easily be the most restrictive portion of the exhaust system. factories sometimes
use smaller ports to reduce flow and power and promote better fuel economy.

PS - if you are going with a custom exhaust setup, be sure to use 2.5" piping or thereabouts. anything much larger will kill the backpressure and you will begin to lose torque.