These unique 6 times merged headers have been specifically designed to improve the performance of stock cast iron heads. Iron lung headers should not be used with less that 10 to 1 compression. The unburned fuel in low compression engines is pulled out of the head and reignites in the exhaust causing high temperatures and often "flaming". When used in combination with a 5" core 2 into 1 muffler and stock heads, increases of up to 25 horsepower and 15 foot pounds of torque are not uncommon. Exhaust diameters should not be restricted after the collectors or the high flow will be disrupted. These are a firing order header, so they can not be installed backwards on the dyno, or modified for use on Ford engines. Iron Lung headers are the greatest advantage in the most restricted applications such as no porting, two barrel carburetors or restrictor plates. Iron Lungs are built with 3/8" thick CNC cut flanges.