Mandrel-bent tubes provide consistent tubing diameters for smooth flow and increases the cylinder scavenging effect and improves engine breathing Heavy duty 16-gauge tubing for increased strength and durability 1-1/2†diameter primary tubes, 1-3/4†diameter secondary tubes for increased exhaust flow increasing performance and improving throttle response 2-1/2†collector for maximum strength and exhaust flow 3/8†thick header flange for a leak-free seal and maximum strength Premium aluminum header gaskets included Available in a high heat resistant black paint or polished finish