DNA Motoring HDS-NS13 Stainless Steel Exhaust Header Manifold Made of high quality Steel with 4-1 direct bolt-on design TIG welded CNC machine flange O2 sensor bung insertion/ metal gasket included/ inlet: 1.875"/ outlet: 2" Increase high flow air, instantly gain 10 to 15 HP./ TQ Application: 89-90 Nissan 240SX S13 SOHC engine only (instruction not included, professional installer is highly recommended)