From the horses mouth: "HKS Hi-Power Exhaust are designed and inspired from endurance and GT racing in Japan. HKS Hi-Power exhaust system offers greater flow and higher-RPM power gains due to less restrictive design by eliminating unnecessary bends for the straightest exhaust path. By smoothing out the exhaust flow, greater exhaust velocity is achieved for better mid-range boost response and high-RPM power. HKS Hi-Power exhaust systems are made from SUS304 stainless steel muffler and tip assemblies."