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.

There is a range of muffler types you can choose from with a cat back exhaust system with most people opting for a glasspack or straight-through muffler. Both of these options are designed to work well within the system to reduce back pressure. Deciding to purchase a performance exhaust system for your car is no easy task.

The only difference is that it features straight perforated pipes. The original exhaust systems focus more on just reducing the sound and not shaping it to give it that desired deep growl. One function shared with both the axle-back and the cat-back exhaust systems are shaping your vehicle’s tone.

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