upright derby style headers fit the 2.8L, 3.1L and 3.4L GM V6 engines with round port exhaust ports. 1-1/2 in. mandrel bent primary tubes provide consistent tubing diameters for smooth flow of the exhaust pulses and increase the cylinder scavenging of the exhaust to improve engine breathing. The headers are constructed from heavy duty 16-gauge 409 stainless steel tubing for increased strength and durability. These headers use a merge collector. The 3/8 in. thick header flange provides a leak-free seal and maximizes strength.