A 100 CPSI metallic core flows far better than standard ceramic cats, which is why these suit performance and race exhaust systems. Match the inlet and outlet internal diameter to your pipe size, and check the body diameter and overall length fit your tunnel or chassis clearance, especially with the heat shield versions. The O2 sensor bung versions accept a standard M18 x 1.5 sensor for tuning or monitoring. Be aware that emissions regulations differ between states and vehicle ages: a high flow cat may not be a legal replacement for a factory converter on a road registered vehicle, so confirm compliance requirements for your vehicle before fitting.