FAST introduces the first "composite" multi-piece Gen III manifold that makes real horsepower and torque. The three-piece modular design was engineered to fit in the stock location, accept all factory hardware, fuel lines, and linkage, and make more power. When seen side-by-side with a factory piece, you can see how this was achieved, and also note some external differences in the runner width and diameter. The fatter LSX runners increase both velocity and volume by moving the air more efficiently.
