The Acura NSX stands as one of the most revered Japanese sports cars ever built. Its mid-engine layout, aluminum monocoque chassis, and VTEC V6 engine set a benchmark for handling and reliability. Yet many owners eventually crave more power. A Stillen supercharger has long been a go-to upgrade for NSX enthusiasts seeking a substantial, reliable horsepower increase without compromising the car’s core character. This article compiles real owner reviews, dyno results, and practical insights to give you an accurate picture of the power gains you can expect from this modification.

What Is the Stillen Supercharger?

Stillen (Steve Millen Sportparts) began developing forced induction kits for the NSX in the late 1990s. The system uses a Vortech V1 or V2 centrifugal supercharger, an air-to-air intercooler, and a dedicated fuel management unit. Designed specifically for the C30A and C32B engines found in the original NSX (1991–2005), the kit is engineered to bolt on without major engine modifications.

The centrifugal design produces linear power delivery that climbs with engine RPM, mimicking a larger-displacement engine rather than the abrupt surge of a twin-screw blower. The included intercooler keeps intake temperatures in check, which is critical for reliability on track days or prolonged spirited driving.

Stillen produced multiple generations of the kit, with later versions featuring improved plumbing, a more efficient intercooler core, and compatibility with OBD-II equipped NSXs. The system is typically configured to run safely on 91–93 octane pump gas, which is a point that owner reviews consistently praise.

Real Owner Horsepower Gains

To determine how much horsepower a Stillen supercharger delivers, we aggregated data from multiple NSX forum threads, dyno sheets posted by owners, and tuner reports. The results are remarkably consistent.

Stock NSX Baseline

The 3.0-liter C30A engine (1991–1996) produces 270 horsepower at the crank, with typical wheel figures around 220–225 hp depending on the dyno and drivetrain losses. The later 3.2-liter C32B (1997–2005) is rated at 290–300 hp with about 240–245 hp at the wheels.

Stillen Supercharger Dyno Results

Owner-reported wheel horsepower after installing a base Stillen kit (5–6 psi boost) on a 3.0-liter NSX:

  • Average gain: 90–110 wheel horsepower
  • Typical final output: 320–340 whp
  • Crank equivalent: 380–410 hp

For the 3.2-liter engine, owners report similar percentage gains:

  • Average gain: 100–120 wheel horsepower
  • Typical final output: 345–365 whp
  • Crank equivalent: 410–430 hp

What About Peak Boost?

The base pulley kit runs 5–6 psi. Some owners upgrade to a smaller pulley for 8–9 psi, which requires larger injectors and a higher-flow fuel pump. With supporting mods, those cars push 370–390 whp (440–460 crank). Several owner reviews on NSXPrime note that 8 psi levels are reliable if the engine is in good health and properly tuned.

Owner Experiences: Street, Track, and Daily Driving

To capture the full range of real-world feedback, we categorized owner reviews by primary use. The responses come from long-time members of the NSX community who have owned their cars for years, often after the supercharger was installed.

Street Performance

Most owners use their NSX as a weekend car. They report that the Stillen supercharger transforms the driving experience without ruining the car’s balance. Throttle response remains sharp thanks to the centrifugal blower’s low parasitic drag at cruising speeds. At 3,000–4,000 rpm the power builds noticeably, and by redline the car pulls with genuine aggression.

  • Owner review (cngNSX, NSXPrime): “My car went from feeling quick to genuinely fast. The supercharger doesn’t change the exhaust note much—it just adds a smooth whistle above 4k rpm. I wouldn’t want a turbo for the street because you’d lose that instant reaction.”
  • Owner review (Silver Bullet, Reddit): “I track mine twice a year, but for the street it’s perfect. Torque in the mid-range is where the NSX needs help, and the Stillen delivers. Passing on the highway is effortless.”

Track and Autocross

Tracking a supercharged NSX requires attention to cooling and braking, but owners who complete those upgrades report strong reliability. The linear power delivery makes it easier to maintain corner exit speeds compared to a turbo, which can catch drivers off guard.

  • Owner review (trackjunkie, NSXCA forums): “I’ve done over 30 track days with my Stillen kit at 8 psi. Oil temps stay fine with an upgraded radiator and oil cooler. The power is consistent lap after lap, and I’ve never had a heat soak issue with the intercooler.”
  • Owner review (VroomVroom, YouTube comments on dyno video): “At my local autocross, the extra 100 whp puts me into a competitive class. The supercharger is reliable enough that I drive it to and from the event without trailering.”

Daily Driver

Only a small number of owners daily drive a supercharged NSX. They caution about the fuel economy penalty (some report a drop of 2–4 mpg) and the added heat from the supercharger unit under the engine cover. Still, many say the thrill of the power offsets the small drawbacks.

  • Owner review (JonM, NSXPrime): “I put 8,000 miles a year on mine, including short commutes. The supercharger is transparent in normal driving. You only notice it when you’re hard on the gas. The biggest downside is that the engine bay gets hot—a heat shield is mandatory.”

Installation and Tuning Process

Installing a Stillen supercharger is a significant project, but it is well-documented. The kit includes the supercharger bracket, intercooler, injection molded intake pipes, bypass valve, and a fuel management computer (Stillen supplied a piggyback unit in early kits). Most owners strongly recommend professional installation and tuning.

Step-by-Step Overview

  1. Preparation: Drain coolant and remove the intake manifold, throttle body, and airbox. The alternator and power steering pump may need repositioning.
  2. Mounting the supercharger: The bracket bolts to the driver’s side of the engine, where the alternator originally sat. The alternator is relocated to a new position on the bracket.
  3. Intercooler installation: The front-mounted intercooler replaces the factory air intake area. Some cutting of the bumper support foam is required.
  4. Plumbing: Charge pipes run from the supercharger to the intercooler and from the intercooler up to the throttle body.
  5. Fuel system upgrades: The kit supplies larger injectors (440cc for base boost) and a fuel pressure regulator. Later generations included a rising-rate fuel pressure unit.
  6. Engine management: The piggyback unit intercepts signals to adjust fuel and timing. Modern owners often replace the old Stillen computer with a standalone system like AEM Infinity or Motec for more precise control.
  7. Tuning: A professional dyno tune is essential. The stock ECU can adapt to a point, but without proper fuel and timing maps, detonation risk rises. Many tuners recommend upgrading to a Science of Speed tune or a dedicated NSX tuning service.

Common Installation Mistakes

Owner feedback identifies three frequent pitfalls:

  • Improper belt tension: The serpentine belt that drives the supercharger must be tensioned carefully. Too loose and it slips under load; too tight and it stresses the bearings.
  • Inadequate cooling: Without upgrading the radiator (or adding an oil cooler), intake temps can climb quickly on hot days, killing power and risking knock.
  • Skipping the in-tank fuel pump upgrade: The stock pump can’t maintain pressure past 6 psi. Many owners who upgraded to 8 psi later had to replace the pump anyway.

Potential Drawbacks and Considerations

Despite overwhelmingly positive owner reviews, the Stillen supercharger has real downsides. Understanding them helps set realistic expectations.

Cost

Complete used kits typically sell for $3,500–$5,000 on forums. New old stock (rare) or professionally refreshed kits command $5,500–$7,000. Installation labor, tuning, and supporting modifications (radiator, clutch) can push the total to $8,000–$12,000. That’s substantial for a 30-year-old car.

Reliability

The C30A and C32B engines are stout, but any forced induction system adds stress. Owners report that a well-maintained, properly tuned kit runs 50,000+ miles without issues. However, bypass valve failures, intercooler leaks, and belt wear are common after 30,000 miles. Regular inspection of the supercharger oil (the Vortech unit requires oil changes every 15,000 miles) is critical.

Clutch and Transmission Wear

The factory NSX clutch was designed for ~270 lb-ft of torque. After a supercharger, torque climbs to 280–320 lb-ft at the crank. Several owners in the NSXPrime Stillen supercharger thread note clutch slip within two years of installation. Upgrading to a stage 1 or stage 2 clutch kit from SOS or OEM+ components is recommended.

Insurance

Disclosing a forced induction modification to your insurance carrier can increase premiums by 15–30%, depending on the provider. A few owners report being non-renewed after their insurer learned of the modification. Always confirm coverage before installing.

Heat Management

The engine bay of the NSX is tight. The supercharger component radiates heat, and without additional shielding, the engine cover paint can discolor over time. Thermal wraps, ceramic coating on headers, and a heat-reflective blanket for the supercharger are common owner solutions.

Comparing the Stillen to Other Supercharger Options

Several other kits exist for the NSX, including the LoveFab turbo conversion, the Autorotor (Lysholm) twin-screw kit, and custom centrifugal setups from smaller fabricators. The Stillen kit remains popular because it is reversible, well-documented, and retains the stock exhaust manifold and catalytic converters, making it smog-legal in many states (CARB EO status varies by year and chassis).

Compared to a twin-screw supercharger, the Stillen offers lower peak torque but better top-end power. For track work, the linear delivery is easier to manage. For autocross, the twin-screw’s instant torque at low RPM may be more beneficial. Owner reviews on NSXCB highlight that the Stillen kit is the most common starting point, with current owners recommending it for anyone who wants a proven, moderate power increase (up to 400 hp) without chasing a high-boost build.

Conclusion

Based on extensive owner feedback, the Stillen supercharger can reliably add 100–120 wheel horsepower to a standard Acura NSX, translating to a combined output of 380–430 crank horsepower depending on boost level and engine version. The power delivery is smooth, the kit is well-engineered for the chassis, and with proper installation and tuning, long-term reliability is achievable.

However, the total investment is significant and goes beyond the kit itself. Clutch upgrades, cooling improvements, and professional tuning are essential, not optional. Prospective buyers should budget accordingly and seek out an experienced NSX mechanic. The Stillen supercharger is not a magical “bolt-on and go” solution, but for those who proceed thoughtfully, it delivers the driving experience that the NSX always deserved from the factory.