The Mitsubishi 3000GT VR4 is an iconic performance machine, but its stock exhaust system is a known bottleneck. Replacing it with a high-flow unit like the HKS Twin Power Exhaust can unlock significant power, improve throttle response, and give the VR4 a more aggressive voice. This guide covers everything you need to know about the HKS system: its design, real-world performance gains, a detailed installation process, and a full cost breakdown to help you budget for the upgrade.

Understanding the HKS Twin Power Exhaust System

HKS has been a leading name in Japanese performance parts for decades, and the Twin Power exhaust for the 3000GT VR4 exemplifies their engineering philosophy. Unlike a simple cat-back, this system is a full turbo-back design (downpipes, catalytic converters, and cat-back) aimed at reducing backpressure while maintaining a refined tone.

  • Materials: Constructed from T304 stainless steel with mandrel-bent tubing for smooth flow. The muffler uses a straight-through design packed with sound-absorbing materials to control resonance.
  • Weight Reduction: The HKS system saves roughly 15–20 lbs over the factory exhaust, primarily by replacing heavy cast-iron downpipes and the large stock muffler.
  • Sound Profile: It produces a deep, aggressive note under load without excessive drone at highway speeds. Many owners describe it as “purposeful but livable.”
  • Compatibility: Designed specifically for the 1991–1999 Mitsubishi 3000GT VR4 (and closely related Dodge Stealth RT/TT). It retains factory O2 sensor and exhaust hanger locations for a straightforward bolt-on fit.
“The HKS Twin Power is a true turbo-back system that maximizes flow without sacrificing daily drivability. It’s one of the most popular upgrades on the VR4 platform.” — 3SX Performance

Performance Gains: What to Expect

Installing the HKS Twin Power Exhaust yields noticeable improvements across the RPM range. While gains vary depending on other modifications and tuning, most stock VR4s see:

  • Horsepower Increase: 15–25 wheel horsepower (depending on vehicle condition and whether a tune is applied). The reduction in backpressure allows the twin turbos to spool more freely.
  • Torque Improvement: A flatter torque curve with 20–30 lb-ft more in the midrange (3,000–5,000 RPM). This improves acceleration roll-on from highway speeds.
  • Faster Turbo Spool: The freer-flowing downpipes and catalytic converters reduce exhaust gas temperature post-turbine, helping the turbos reach full boost 300–500 RPM sooner.
  • Weight Savings: Every pound of unsprung and drivetrain weight reduction contributes to quicker acceleration and better handling.

For the best results, combine this exhaust with an intake upgrade and a boost controller. A basic tune is not strictly required, but a flash or piggyback ECU will extract the full potential. Without tuning, the factory ECU will adapt to the better flow within its parameters, but you won’t gain everything the system can offer.

Installation Walkthrough

Installing the HKS Twin Power Exhaust at home is feasible with basic mechanical experience and the right tools. Allow 3–5 hours for a first-time install. Below is a detailed, step-by-step guide.

Necessary Tools & Supplies

  • Socket set (10mm, 12mm, 14mm, 17mm, 19mm)
  • Wrench set (same sizes)
  • 6-point impact sockets for stubborn bolts
  • Jack and four jack stands (safely lift entire car)
  • Exhaust hanger removal pliers or screwdriver
  • Penetrating oil (WD-40 or PB Blaster)
  • Torque wrench (50–150 N·m range)
  • New exhaust gaskets (included with HKS kit, but have spares)
  • O2 sensor socket (22mm) if removing downpipe sensors
  • Safety glasses and gloves

Precautions

Work on a level surface. The VR4 has low ground clearance, so raising it high enough to slide under is critical. Use jack stands rated for at least 3 tons. Never rely solely on a floor jack.

Step 1: Prepare the Vehicle

Disconnect the battery negative terminal to avoid shorting O2 sensors. Loosen the lug nuts, raise the car, and place stands under the factory lift points. Remove all four wheels for easier access.

Step 2: Remove the Stock Exhaust

  1. Spray penetrating oil on all exhaust flange bolts, O2 sensor bungs, and rubber hangers. Let it soak for 10 minutes.
  2. Unplug the two O2 sensors from the downpipes (one on each side). Use the 22mm socket to unscrew them. Be gentle to avoid breaking the sensor.
  3. Remove the bolts connecting the downpipes to the turbo outlets. These are often tight; use a 14mm swivel socket if needed. There are three bolts per side.
  4. Support the stock downpipes and cat-back sections with a jack or helper. Remove the mid-pipe bolts (12mm) and hangers near the transmission mount.
  5. Slide the stock system out from under the car. It’s heavy and awkward—get help if necessary.

Step 3: Install the HKS System

  1. Transfer the O2 sensors to the HKS downpipes. The kit provides new bungs; use anti-seize on the threads.
  2. Install the HKS downpipes loosely. Use new gaskets provided in the kit. Hand-tighten the flange bolts to the turbos.
  3. Attach the catalytic converter test pipes or high-flow cats (depending on your HKS version). These bolt to the downpipes.
  4. Slide the cat-back section into position. Hook the rubber hangers onto the chassis tabs. You may need to lube the hanger holes with silicone spray.
  5. Align all flanges and slip joints. Tighten all hardware to 35–45 N·m (26–33 lb-ft) for the downpipe-to-turbo bolts, 30–40 N·m (22–30 lb-ft) for mid-pipe and cat-back connections. Use a torque wrench.
  6. Reattach O2 sensor connectors. Ensure the wiring is clear of moving suspension parts and heat sources.

Step 4: Final Checks

Lower the car and start the engine. Listen for exhaust leaks at every joint. A slight “ticking” sound indicates a leak—tighten the suspect flange or replace the gasket. Check the O2 sensor wiring for contact with the exhaust. Take a short test drive and inspect again after the system heats up and cools down.

Cost Breakdown

Budgeting for this upgrade requires considering more than just the exhaust kit. Here’s a realistic estimate:

  • HKS Twin Power Exhaust Kit: $850–$1,200 (prices vary by retailer; check HKS USA and 3SX Performance for current pricing).
  • Professional Installation: $200–$400 (pricing depends on shop labor rates; expect 3–5 hours at $75–100/hr). DIY saves this cost.
  • Additional Parts: New fasteners (ARP or OEM) ~$30; replacement O2 sensors if yours are old ~$100–150; exhaust gaskets (spare set) ~$20; anti-seize and penetrating oil ~$15.
  • Tuning (Recommended): Basic ECU flash or piggyback ~$300–$600. Without tuning you still get gains, but tuning ensures optimal air/fuel ratios and timing for the free-flowing exhaust.

Total cost: Expect to spend $1,100–$2,000 depending on DIY vs. professional install and whether you tune immediately. This is a very effective performance-per-dollar upgrade.

Alternatives to Consider

While the HKS Twin Power is a stellar choice, other quality exhaust systems exist for the VR4:

  • GReddy Power Extreme: Similar design but slightly louder. Often $100–$200 less expensive.
  • RSR ExMag: Lighter and more cost-effective, but fitment can be tricky on some model years.
  • Custom Turbo-Back: Using Vibrant or A’PEXi components can yield comparable flow, but you lose the warranty and hassle-free bolt-on fit.

If you prioritize proven fitment and sound refinement, HKS remains the gold standard for the 3000GT VR4.

Maintenance and Longevity

Stainless steel resists corrosion, but the VR4’s hot and damp engine bay can still cause some surface discoloration. Regularly inspect exhaust hangers (the rubber degrades over time) and check for loose bolts after the first 500 miles. Re-torque all flange bolts at that interval. If you drive in winter salt, consider a ceramic coating or protectant on the exhaust to keep it looking good.

Final Thoughts

The HKS Twin Power Exhaust is more than a sound upgrade—it’s a genuine performance part that improves every aspect of the VR4 driving experience. With careful installation and a reasonable budget, you’ll unlock the potential of Mitsubishi’s twin-turbo V6 while enjoying a cleaner, more aggressive exhaust note. Whether you choose the DIY route or hire a shop, this upgrade will reward you each time you hit the throttle.

For more information and owner reviews, visit the 3SI Online Forums and Stealth 316—two excellent resources for VR4 enthusiasts.