These Trick Flow GenX® 205 cathedral port cylinder heads for GM 4.8L/5.3L LS Vortec engines are fully CNC-machined to significantly increase the performance of GM cars and trucks. Trick Flow engineers altered the valve angles from 15° to 13.5° to decrease valve shrouding, increase mid-lift airflow, and improve rocker arm-to-valve cover clearance. Material was added at the rocker arm mounting points to increase high-rpm valvetrain stability. The spark plugs were relocated in the CNC-profiled combustion chambers to enhance mid-lift airflow and increase the rigidity of the casting for extreme horsepower applications. Top-of-the-line CNC Competition Ported runners have a premium high resolution surface finish for maximum flow and performance.