Why Upgrade to an HKS Exhaust on Your Mitsubishi Evo X?

The Mitsubishi Lancer Evolution X is already a performance icon, but the factory exhaust system is restrictive, heavy, and designed to meet noise regulations rather than unlock the car’s true potential. Swapping in an HKS exhaust system delivers tangible gains: increased horsepower (typically 10–20 whp depending on the system), a more aggressive and refined exhaust note, and significant weight savings of 15–25 pounds off the unsprung mass. HKS is a renowned Japanese performance brand with decades of experience in turbocharged platforms, and their Evo X exhausts are engineered for bolt-on fitment, durability, and maximum flow. Whether you choose the HKS Hi-Power, Legamax, or Super Turbo system, the installation process is similar and rewarding for the DIY mechanic.

Tools and Materials You’ll Need

Gather these items before starting to avoid interruptions. Quality tools make the job safer and faster.

  • HKS exhaust system – Confirm it matches your Evo X model year (2008–2015).
  • Floor jack and two jack stands – Rated for at least 3 tons each.
  • 3/8″ and 1/2″ drive socket set – Metric sockets, particularly 10mm, 12mm, 14mm, and 17mm.
  • Combination wrench set – Same sizes as sockets for stubborn fasteners.
  • Torque wrench – 1/2″ drive with range 20–150 ft-lb.
  • Penetrating oil – WD-40 Specialist or PB Blaster.
  • Safety glasses and mechanic’s gloves.
  • RTV silicone or new exhaust gaskets (if not included with the HKS kit).
  • Wire brush or steel wool – To clean flanges.
  • Spring clamp pliers – For disconnecting factory hangers if needed.

Preparing the Vehicle for Exhaust Work

Safety first. Park the Evo X on a level concrete surface. Apply the parking brake firmly, then place wheel chocks behind the rear tires. Disconnect the negative battery terminal – this prevents any accidental electrical shorts and also resets the ECU’s learned fuel trims, which helps the car adapt to the new exhaust during the first drive cycles.

Raise the rear of the car with the jack, positioning the jack under the center rear differential crossmember. Place jack stands under the designated lift points on the rear frame rails (consult your owner’s manual). Lower the car gently onto the stands. Shake the vehicle to ensure it’s stable. Crawl underneath and verify you have sufficient clearance.

Removing the Factory Exhaust System

Step 1 – Apply Penetrating Oil

Spray penetrating oil onto every exhaust nut and bolt you can see: the turbo-to-downpipe bolts, the mid-pipe flange bolts, the axle-back connections, and the exhaust hanger rubber isolators. Let the oil soak for at least 10 minutes while you prepare other tools.

If you are doing a full cat-back or turbo-back system, start at the rear. Loosen the bolts connecting the mid-pipe to the axle-back muffler section. You may need to twist the rubber hangers to slide the pipe free. Support the heavy muffler with a second jack or a helper to avoid stressing the hangers. Set the stock axle-back aside.

Step 3 – Disconnect the Center Mid-Pipe

Locate the mid-pipe flange under the center of the car. Use a 14mm socket to remove the two bolts. The mid-pipe is often suspended by two rubber hangers; pull the metal posts out of the rubber isolators. If they are stuck, apply more penetrating oil and twist with pliers.

Step 4 – Remove the Downpipe (If Replacing with HKS Downpipe)

Some HKS kits include a downpipe. For this, you’ll need to access the turbo-to-downpipe hardware. Use a long extension and a universal joint socket to reach the upper bolt. These bolts are notorious for seizing; apply heat from a propane torch if penetrating oil alone doesn’t work. Once the bolts are out, carefully wiggle the downpipe down past the steering intermediate shaft (if applicable).

Step 5 – Clean All Flanges

With the entire factory exhaust removed, use a wire brush or steel wool to clean the turbo outlet flange, mid-pipe flanges, and any mounting surfaces. Remove all carbon deposits and old gasket material. A clean surface ensures a leak-free seal with the new HKS gaskets.

Installing the HKS Exhaust System

Unbox the HKS system and lay out all components: downpipe (if included), mid-pipe, muffler section, hardware bag, and hangers. Compare with the installation manual – HKS typically provides clear instructions.

Step 1 – Install the Downpipe (If Applicable)

Fit the downpipe onto the turbo outlet. Use new gaskets (copper or multi-layer steel). Tighten the bolts hand-tight first, then stagger them to spec. Torque to 30–35 ft-lb for M10 bolts. Do not overtighten stainless steel hardware as it can gall.

Step 2 – Assemble the Mid-Pipe Section

Slide the mid-pipe into position, aligning the flanges with the downpipe or front pipe outlet. Many HKS mid-pipes have a flexible joint; ensure this section is oriented correctly. Install the supplied bolts and gaskets, but leave them hand-tight to allow adjustment later.

Step 3 – Mount the Axle-Back (Rear Section)

Hang the rear muffler section on the factory rubber isolators. The HKS system usually uses the existing hanger locations – the tip alignment should be centered in the bumper cutout. Adjust the angle by sliding the adjuster brackets (some kits have slotted holes).

Step 4 – Connect All Flanges and Torque

With all sections loosely connected, verify that the exhaust does not contact the underbody, chassis braces, or the rear sway bar. Rotate pipes as needed. Then, using a torque wrench, tighten all flange bolts in a star pattern to 30–35 ft-lb. For spring-loaded bolts on HKS systems, follow the included torque specs (usually slightly lower).

Step 5 – Reinstall Exhaust Hangers

Push the metal posts back into the rubber hangers. If the HKS system uses different hanger bushings, use them. The exhaust should sit with an even gap around the bumper tip opening. Re-check clearance after tightening.

Post-Installation Checks and Testing

Once everything is installed, perform these critical checks before lowering the car:

  • Leak test: With the battery reconnected, start the engine (on jack stands) and let it idle. Place a gloved hand near all flanges – feel for air pulses. If you hear a ticking or hissing, tighten bolts slightly further or replace the gasket.
  • Clearance inspection: Turn the steering full left and right; ensure the exhaust doesn’t contact the steering shaft or subframe. Also check the heat shield clearances.
  • Smoke test (optional): A shop can blow smoke through the intake to detect tiny leaks – useful for turbo-back installations.

Lower the vehicle. Test drive gently for the first 5 minutes, then accelerate through various RPMs. Allow the exhaust to heat-cycle and the ECU to adapt. You may notice a slightly rich smell initially – this is normal for new exhausts as excess assembly oil burns off.

Tuning Considerations After Exhaust Upgrade

While the HKS cat-back system alone does not require a tune, adding a downpipe and test pipe will trigger a check engine light (CEL) due to the removed catalytic converter. To fully capitalize on the increased airflow, an ECU flash (e.g., from COBB Tuning Accessport, EcuTek, or a custom dyno tune) is highly recommended. Without a tune, the stock fuel and ignition maps may be overly rich or cause knock under high load. A proper tune can net an additional 15–30 whp beyond the exhaust alone.

Consider pairing the HKS exhaust with an upgraded intercooler, intake, and boost controller for a balanced stage 2 setup. Check reputable tuning resources like COBB Tuning or EvoScan for guidance on your specific year.

Maintenance and Long-Term Care

HKS exhausts are typically made of T304 stainless steel, which resists corrosion, but the tips may require occasional polishing. After the first 500 miles, re-torque all flange bolts as they can settle. Inspect the gaskets for leaks annually, especially if the car sees track use or winter salt.

For more details on HKS specific products, visit the official HKS website. Community forums like EvolutionM.net offer extensive user reviews and troubleshooting tips for Evo X exhaust installations.

Final Thoughts

Installing an HKS exhaust on your Evo X is one of the most satisfying and rewarding modifications you can perform in a single afternoon. The sound, power, and weight reduction transform the driving experience. By following this detailed guide, you ensure a professional-quality install that will provide years of trouble-free performance. Take your time, use the right tools, and enjoy the growl of your new setup.