There are subtle changes on the outside to let onlookers know that this is no ordinary F-150, such as a custom dual-intake hood, a custom front fascia and grille combo, and Shelby badging. For the interior, Shelby adds carbon-fiber trim, billet racing pedals, custom floor mats, and a serialized plaque. For lean-burn spark-ignition engines, an oxidation catalyst is used in the same manner as in a diesel engine. Emissions from lean burn spark ignition engines are very similar to emissions from a diesel compression ignition engine. Upon failure, a catalytic converter can be recycled into scrap.

By running pipes from the catalytic converter to the muffler and from the muffler to the exhaust tip, cat back exhaust systems improve exhaust gas flow, providing small performance boosts. However, your performance gains may be limited if your catalytic converter restricts gas flow, as a catback exhaust system is installed ‘downstream’ of the converter. Header-back systems are increasingly rare, namely because of modern emissions systems. Since removing your vehicle’s factory emissions components is highly illegal, the previous two options are more common. However, header-back systems are still available for some older, pre-emissions applications. In these cases, header-back systems offer more performance and volume than cat-back or axle-back systems