Doug's Headers D313 1-3/4" 4-Tube Full Length Exhaust Header for Chevrolet Camaro Big Block Chevrolet 67-74 Thick flanges (3/8 inch to 5/8 inch); no warping CNC mandrel bent tubes; accurate fit & better flow Precision formed long transition collectors; reduces backpressure Heavy gauge tubing (16 & 14G); longer life Header tubes are pre-polished; better appearance