"Factory exhaust" refers to the system in a vehicle that releases the gases produced by the engine. It includes the pipes, muffler, and other components designed and installed by the manufacturer. Full definition
It looks great, you've added performance parts but the restrictive factory exhaust system needs help and doesn't live up to the sound you expect. (pfyc.com)
Toss out your restrictive and inefficient factory exhaust manifold for the increased exhaust flow and big boosts in torque and horsepower delivered by aFe Power's PFADT headers. (carparts.com)
Engine braking, not normally a diesel strong suit, was surprisingly good; the truck doesn't offer factory exhaust brake, but the 3.0 - liter diesel's variable - nozzle turbo can create sufficient backpressure to serve the same purpose, and it did a nice job keeping speed in check on downgrades. (automobilemag.com)