The K&N 57-2555 is a cold air intake kit for the 2003-2004 Ford Mustang Mach 1 coupe with the 4.6L DOHC V8. It replaces the factory airbox and intake tube with a plastic tube, a heat shield that fits into the old airbox space, and a washable, reusable oiled cotton filter. Owners on user forums say gains on a stock car are modest, and one Mach 1 owner was unsure the kit added power over the stock airbox without a custom tune. Its advantage is the reusable filter, which can be cleaned and re-oiled instead of replaced, and a properly made kit avoids the emissions and build-quality doubts that user forums raise about cheap no-name intakes. Search terms this kit matches include 2003 Mach 1 cold air intake, 4.6 DOHC Mach 1 CAI, and K&N 57-2555 intake kit.
Installation is a bolt-on job. The manufacturer's install sheet calls for basic hand tools, including a flat-blade screwdriver, 10mm and 5/8" wrenches, a ratchet with extension, 8mm and 10mm sockets, and a 5mm Allen wrench. Disconnect the negative battery cable first, then unplug the mass air sensor, which is reinstalled on the new tube. The manufacturer recommends keeping the factory intake rather than discarding it, and states the kit is not designed for vehicles with a body lift. User forums warn that any opening left past the mass air sensor lets unmetered air in and can run the engine lean, so cap or seal every vent and hose connection.
The manufacturer recommends that customers do not discard the factory air intake, so keep it in case you need to return the car to stock.
The manufacturer states this kit was not designed to fit vehicles with a body lift, so check your ride height before ordering.
The manufacturer's install sheet lists the tools above and begins by having you turn the ignition off and disconnect the negative battery cable. Expect to disconnect the mass air sensor connector, loosen the throttle-body hose clamp, remove the air cleaner mounting bolt from the inner fender, and detach the crankcase vent hose before removing the factory intake assembly. Plan for the mass air sensor to be unbolted from the airbox and fitted to the new tube, and be careful with the crankcase vent fitting, which the sheet has you install into the tube. Keep the hardware organized, because the mass air sensor and clamp torque matter for a reliable seal.
