Doug's Headers D590 1-3/4" 4-Tube Full Length Exhaust Header for Pontiac GTO 326-455 68-72 Thick flanges (3/8 inch to 5/8 inch); no warping CNC mandrel bent tubes; accurate fit &amp; better flow Precision formed long transition collectors; reduces backpressure Heavy gauge tubing (16 &amp; 14G); longer life Header tubes are pre-polished; better appearance