Hi-Power Series™ 409 SS Dual Cat-Back Exhaust System with Split Rear Exit by HKS®. Exhaust Type: Cat-Back. Exhaust Tubing Material: 409 SS. Main Tubing Diameter: 2.36" to 1.97". Exhaust System Sound: Aggressive / Loud. Professionally developed with a racer in mind, this HKS exhaust system provides an easy opportunity to upgrade both the horsepower and sound of your precious vehicle. Made from first class materials, it will serve you for years to come. Hi-Power 409 mufflers offer a cost effective solution for your sports muffler needs. The rear section is made from SUS304 grade stainless steel for a high lustre finish and the piping section which is not visible once fitted is made from coated SUH 409, reducing the cost. SUH409 has other benefits such as being more resistant to thermal expansion and improved acoustic properties. SUH409 has the ability to absorb more sound than SUS304 which allows Hi-Power 409 mufflers to have a straight through design without fear of excessive noise.