Overview of the HKS Super Sequential Dual Exhaust for the Mitsubishi 3000GT

The Mitsubishi 3000GT (also known as the GTO in Japan) remains a highly regarded sports car from the 1990s, celebrated for its advanced technology and all-wheel-drive capabilities. Among the most impactful upgrades owners can make is replacing the restrictive factory exhaust system with an aftermarket unit. The HKS Super Sequential Dual Exhaust has long been a favorite among enthusiasts, praised for its blend of performance gains, weight savings, and distinctive exhaust note. This article provides a thorough examination of the costs, installation process, and tangible benefits of fitting this system to your 3000GT, helping you decide if this modification aligns with your goals.

What Makes the HKS Super Sequential Dual Exhaust Unique?

HKS is a Japanese tuning company with decades of experience in high-performance exhaust systems. The Super Sequential Dual Exhaust is specifically engineered for twin-turbocharged models like the 3000GT VR-4, as well as naturally aspirated variants. Its key innovation lies in the dual exhaust layout featuring a main muffler and a secondary sequential valve. At low RPMs, exhaust gases flow through both mufflers to keep noise levels compliant; as RPMs climb, the secondary valve opens to allow a more free-flowing path, reducing backpressure and unlocking top-end horsepower. This design gives the 3000GT a civilized idle and a ferocious roar under full throttle.

The system is constructed from T304 stainless steel, ensuring corrosion resistance and long-term durability. Mandrel-bent tubing maintains consistent internal diameter for optimal flow, and all welds are precision TIG welded for strength and a clean appearance. The kit includes all necessary gaskets, hardware, and hangers for a direct bolt-on installation.

Cost Breakdown for the HKS Super Sequential Dual Exhaust

Understanding the total investment required is critical before starting this project. Costs fall into several categories: the exhaust system itself, labor, and potential ancillary expenses.

Parts Cost

As of current market pricing, the HKS Super Sequential Dual Exhaust for the Mitsubishi 3000GT typically ranges from $800 to $1,200 depending on the retailer, vehicle variant (VR-4 vs. base model), and whether the system includes downpipes or test pipes. This price is for the cat-back portion; if you need a full turbo-back system including catalytic converter replacements or downpipes, expect to pay closer to $1,600–$2,000. Reputable online vendors such as Import Image Racing and Stealth316 (a dedicated 3000GT/Stealth resource) often stock these systems.

Labor Costs

If you hire a professional mechanic, installation labor typically runs between $150 and $350. The job is considered moderate; the factory exhaust must be unbolted from the cat-back and dropped, and the HKS unit is then fitted with new gaskets. Some shops charge by the hour (around $100–$150 per hour), and the job usually takes 1.5–3 hours depending on rusted fasteners or additional modifications. For owners with basic mechanical skills, a DIY installation can save this entire cost.

Hidden and Additional Costs

Several unforeseen expenses can arise:

  • Gaskets and hardware: While the HKS kit includes gaskets, upgrading to copper or multi-layer steel gaskets (around $20–$40) can improve sealing at high temperatures.
  • Exhaust hangers: Rubber hangers may need replacement if the originals are brittle (approx. $15–$30).
  • O2 sensor relocation: Some versions require extending or relocating the rear oxygen sensor, potentially needing a weld-in bung and wiring extension ($10–$30).
  • Local emissions regulations: If the system deletes catalysts, you may need a high-flow catalytic converter or test pipe to pass inspection (cost varies, typically $100–$300).
  • Custom tuning: After installing a free-flowing exhaust, a re-tune via a piggyback ECU or flash (such as a MOTEC or ECMLink) can fully optimize power gains; expect $300–$600.

Performance Benefits: Horsepower, Torque, and Sound

The primary reason owners invest in this exhaust is the measurable improvement in both performance and auditory experience. Let's break down the specific gains.

Peak Horsepower and Torque Gains

On a 3000GT VR-4, a stock exhaust system is restrictive, especially at higher RPMs. The HKS Super Sequential Dual Exhaust reduces backpressure significantly. Independent dyno tests on the VR-4 platform show gains of 15–25 horsepower and 20–30 lb-ft of torque at the wheels when combined with a free-flowing downpipe. The sequential valve ensures that low-end torque is not sacrificed; instead, the torque curve becomes broader and more linear.

Weight Reduction

The factory exhaust on a 3000GT is heavy, often weighing approximately 45–55 pounds for the cat-back section. The HKS stainless steel system typically weighs around 25–30 pounds, saving roughly 20–25 lbs. This weight reduction, while modest, contributes to improved handling and acceleration, especially when combined with other lightweight modifications.

Sound and Noise Levels

Perhaps the most immediate difference is the sound. The HKS Super Sequential system produces a deep, aggressive tone without the raspiness common with cheaper exhausts. At idle, it remains low and cultured; under heavy throttle, the sequential valve opens fully, releasing a powerful roar that complements the VR-4's twin-turbo spool. The exhaust is known for its smooth transition between muffler modes, avoiding droning at highway cruising speeds. For daily driving, the system is remarkably refined, yet it transforms into a track-ready scream when pushed.

Improved Exhaust Flow and Turbo Spool

Reducing backpressure helps the twin turbos spool slightly faster. You may notice a quicker boost threshold and more responsive throttle tip-in. This is especially beneficial for enthusiasts who have upgraded the turbochargers or intercooler.

Detailed Installation Guide for the HKS Super Sequential Dual Exhaust

Installing the exhaust yourself can save labor costs and give you a deeper understanding of your car. Below is a comprehensive step-by-step process tailored for the 3000GT.

Required Tools and Equipment

  • Floor jack and two jack stands (or a lift)
  • Penetrating oil (e.g., PB Blaster)
  • Socket set with 10mm, 12mm, 14mm, and 17mm sockets
  • Wrench set (combination wrenches)
  • Breaker bar for stubborn bolts
  • Exhaust hanger removal tool (or flathead screwdriver and pliers)
  • Safety glasses and gloves
  • New gaskets (if not using included ones)

Step 1: Prepare the Vehicle

Park on a level surface, engage the parking brake, and chock the rear wheels. Jack up the rear of the car and place jack stands securely under the designated lift points. Allow the exhaust to cool completely if the car was run recently.

Step 2: Remove the Factory Exhaust System

Spray all exhaust bolts and hanger rubber isolators with penetrating oil and let soak for 10 minutes. Starting from the rear, unbolt the muffler section from the mid-pipe using a 12mm or 14mm socket. Slide the hangers off the rubber mounts using the removal tool or a screwdriver. Next, unbolt the mid-pipe from the catalytic converter (or downpipe if the cat has been removed). Lower the mid-pipe and muffler sections carefully; you may need to remove the spare tire well cover for clearance. If any bolts are seized, a breaker bar or impact wrench is helpful.

Step 3: Transfer Hangers and Sensors

If your HKS system requires reusing any factory hangers or rubber isolators, remove them now. Also, if the system includes a provision for the oxygen sensor, unscrew the sensor from the factory pipe and install it into the new system using anti-seize compound on the threads.

Step 4: Install the HKS Super Sequential Dual Exhaust

Position the new HKS mid-pipe and muffler sections loosely. It's easier to hang the muffler on the rubber hangers first, then attach the mid-pipe to the catalytic converter flange. Ensure gaskets are aligned correctly. Hand-tighten all bolts and nuts to allow for adjustment. Once everything is hanging evenly and not touching the underbody, torque the bolts to the factory specification (usually 30–40 ft-lbs). Double-check all connections: the sequential valve actuator wiring must be routed away from hot surfaces.

Step 5: Test for Leaks and Clearance

Lower the car and start the engine. Check for any exhaust leaks at flanges or around the oxygen sensor bung. Listen for rattles against the chassis; you may need to adjust hanger placement or add a washer to shift the muffler away from the bumper. Rev the engine gently to ensure the sequential valve opens and closes correctly.

Maintenance and Longevity of the HKS Exhaust

Stainless steel exhausts require minimal maintenance, but a few practices will extend the system's life:

  • Regular cleaning: Wash the exhaust tips and polished sections with soap and water to remove brake dust and road grime. Use a stainless steel polish twice a year.
  • Check fasteners: After the first 100 miles, retorque all exhaust bolts as the gaskets compress.
  • Inspect hangers: Rubber hangers can degrade; replace them if they show cracks.
  • Address rust: While stainless is corrosion-resistant, surface rust can form in areas where heat cycles break the passivation layer. Light rust can be brushed off with a fine Scotch-Brite pad.

Comparing the HKS Super Sequential with Other Exhaust Options

Before committing, it's useful to see how this system stacks up against alternatives.

HKS Hi-Power Exhaust

HKS also offers a simpler Hi-Power exhaust for the 3000GT. It lacks the sequential valve but is less expensive ($600–$900). It provides similar horsepower gains but can be louder and droney at highway speeds. The Super Sequential is superior for daily drivers who want a dual personality.

GReddy EVO 2 Exhaust

The GReddy EVO 2 is another popular option, known for its muted but aggressive sound. It uses a different muffler design and is slightly heavier than the HKS. The EVO 2 is more affordable ($500–$700) but does not offer the variable exhaust note of the Super Sequential. For raw sound and weight savings, the HKS is the better choice.

Borla Exhaust Systems

Borla offers custom-tuned mufflers that produce a unique tone, but they are often more expensive ($1,000–$1,500) and heavier. Their sound is more of a deep rumble compared to HKS's Japanese-style scream.

Who Should Install the HKS Super Sequential Dual Exhaust?

This exhaust is ideal for owners who value both track-ready performance and daily drivability. The sequential valve makes it one of the most refined aftermarket exhausts for the 3000GT. It is particularly recommended for VR-4 owners looking to free up top-end horsepower without sacrificing low-end torque. Naturally aspirated 3000GT owners will also see benefits, though gains will be smaller (around 8–12 hp) due to the less restrictive stock system on N/A models.

If you plan to eventually add larger turbos, upgraded intercoolers, or engine management, the HKS exhaust provides a solid foundation that won't become a bottleneck.

Final Considerations Before Buying

Ensure you purchase the correct version for your specific model year and drivetrain (VR-4 vs. base). The earlier 3000GTs (1991–1993) have slightly different routing than later models. Websites like 3SX Performance specialize in 3000GT parts and can confirm compatibility. Also, check local noise ordinances; while the HKS is reasonably quiet at idle, some tracks or regions have strict decibel limits.

Installation is straightforward for a competent DIYer, but if you lack experience, hiring a shop with 3000GT familiarity is worth the extra cost. Finally, consider a dyno tune after installation to fully exploit the improved airflow—this can yield 5–10 additional horsepower over a simple drop-in.

Conclusion

The HKS Super Sequential Dual Exhaust is a high-quality, thoughtfully engineered upgrade for the Mitsubishi 3000GT. With parts costs ranging from $800 to $1,200 and professional installation adding $150 to $350, the total investment of roughly $1,000 to $1,500 delivers noticeable performance gains, weight reduction, and a signature exhaust note. The sequential valve technology sets it apart from conventional cat-backs, offering the best of both worlds: civilized cruising and thrilling acceleration. For enthusiasts committed to extracting maximum potential from their 3000GT while preserving daily usability, this exhaust represents an excellent balance of cost and benefit.