The Borla 60521 is a pair of over-axle mid-pipes for the S197 Mustang, and the "X Pipes" in its listing title is a naming error. The manufacturer describes 60521 as a mid-pipe that joins its axle-back system to its separate X-pipe (60513) to form a complete cat-back. Swapping out the factory over-axle sections for these 2.75-inch mandrel-bent stainless pipes removes the flat spots and resonators that restrict flow, so the upgrade gains more than a louder note. It also costs less than replacing the whole system at once. The 2011-2014 Mustang GT and GT500 owners searching for a Borla S197 cat-back upgrade, a 2011-2014 Mustang GT over-axle pipe, or a delete-resonator exhaust will find this is the piece that connects the rear of the system.
Fitment is straightforward on the 2011-2014 GT. Coverage for the GT500 and Boss 302 varies by source, so confirm the exact model year and trim with the manufacturer before ordering. The pipes use the factory ball-and-socket style connections and reuse the original hardware, which is what makes this a bolt-in swap and not a fabrication job. Borla's installation sheet for the GT and GT500 cat-back calls for a hoist or hydraulic lift, a 3/8-inch ratchet with a 3-inch extension, a 15mm deep well socket, a pry bar, a flat-blade screwdriver, and spray lubricant. Plan on a lift and penetrating lube before you start.
The manufacturer designs these over-axle pipes to be used with its rear section and X-pipe, which together complete a cat-back system. Ordering the X-pipe (60513) and an axle-back kit alongside them is the intended setup.
Fitment for the GT500 and Boss 302 is reported differently across sources, and the Mustang GT is the most consistently listed application. Confirm your exact year and trim with the manufacturer before purchase.
This is a moderate-difficulty job that is manageable for a home mechanic with a lift. Per the manufacturer's install guidance, lubricate the hangers and rubber isolators before removing the original parts, and check that the clamps are tightened only once the pipes sit in the correct position with proper tip alignment. Borla advises against air impact tools on its exhaust fasteners because they can bend flanges or damage gasket surfaces and cause leaks. Keep the factory clamps and hardware for reuse, and route the fuel line heat shields away from the pipes before final tightening.
