PLM Subaru WRX STI Axle-Back Exhaust Installation

By Aftermarket Car Parts -Private Label Mfg | Published: 2026-10-22

Category: How-to Guides

Learn how to install PLM axle-back exhaust on Subaru WRX STI 2015-2021. Step-by-step guide with tips for a clean DIY upgrade.

Quick answer

Installing a PLM axle-back exhaust on your Subaru WRX or STI takes about 15 minutes with basic hand tools. This guide walks you through the process, from lifting the car to torquing the bolts.

What you need before starting

The PLM axle-back exhaust replaces the stock mufflers with TIG-welded stainless steel pipes that weigh only 16 lbs. The 2.5-inch outer diameter piping and dual 3.5-inch staggered tips give a direct exhaust path. You'll need a socket wrench, 12mm and 14mm sockets, penetrating oil, and jack stands. No special fabrication is required.

Why choose a muffler delete design

PLM calls this a muffler bypass or track pipe because it removes the heavy stock mufflers entirely. The dual-exit layout keeps exhaust flow balanced. This is a popular upgrade for owners who want a louder, more aggressive tone without replacing the entire cat-back system.

Installation steps

Step 1: Prepare the vehicle: Park on a level surface, chock the front wheels, and lift the rear using a jack. Place jack stands under the rear subframe for safety. Apply penetrating oil to the exhaust hanger rubber isolators and the bolts connecting the axle-back to the mid-pipe. Common mistake: skipping penetrating oil can make bolts hard to remove and risk rounding them.
Step 2: Remove the stock exhaust: Use a 12mm socket to remove the two bolts at the flange connecting the axle-back to the mid-pipe. Pull the rubber hangers off the metal studs on the stock mufflers. Slide the stock axle-back out from under the car. Checkpoint: the stock mufflers are heavy; support them while removing the hangers to avoid dropping.
Step 3: Install the PLM axle-back: Position the PLM exhaust under the car. Slide the hanger isolators onto the studs of the new pipes. Align the flange with the mid-pipe and insert the bolts. Snug the bolts by hand, then tighten to 30-35 ft-lbs using a torque wrench. Common mistake: overtightening can strip the flange threads or warp the gasket.
Step 4: Align the tips and final check: Adjust the dual 3.5-inch staggered tips so they are centered in the bumper cutouts and even on both sides. Tighten the tip clamps if applicable. Start the engine and listen for leaks at the flange. Lower the car and recheck bolt torque after a short test drive. Checkpoint: rattling against the bumper means the tips need realignment.

Product facts

PLM Subaru WRX & STI 2015 - 2021 Axle-Back Exhaust / Muffler Deletes (copy): Constructed from TIG-welded stainless steel, weighing 16 lbs with 2.5-inch outer diameter piping and dual 3.5-inch single wall staggered tips. The lightweight stainless steel construction resists corrosion and reduces rear weight, while the 2.5-inch piping supports a free-flowing exhaust path.
PLM Subaru WRX & STI 2015 - 2021 Axle-Back Exhaust / Muffler Deletes (copy)