Custom Marine Inc., which supplies headers for many engines in the Mercury Racing sterndrive line, has two upgrade kits for the MerCruiser 520. The 520 Sport Tubes will increase horsepower by 48, and improve midrange acceleration and torque. CMI's 520 E-Top Headers increase output by 31 hp and are a direct replacement that will work with existing exhaust outlets. Both styles of header have CMI's patented Cool Collar design and are made with 316L stainless steel. Learn more at custommarine.com.