What Is the GMPP Supercharger Kit for the Impala SS?

The General Motors Performance Parts (GMPP) Supercharger Kit is a factory-engineered forced induction system designed specifically for the 2006–2009 Chevrolet Impala SS, which came equipped with the 5.3L LS4 V8 engine. Priced at $2,500 (street price before installation), the kit is marketed as a bolt-on upgrade that delivers a substantial power increase while retaining drivability and emissions compliance. The core of the system is an Eaton M90 Roots-type supercharger—the same unit found in the Pontiac Grand Prix GTP and Buick Regal GS—mounted on a custom intake manifold. The kit includes the supercharger assembly, a unique cast-aluminum inlet plenum, fuel injectors (typically 36 lb/hr or equivalent), a high-flow fuel pump module, drive belt and pulleys, heat exchanger, coolant pump, all necessary hoses and brackets, and a GM-approved calibration (PCM reflash or handheld tuner with preloaded tune). Claimed gains are approximately 100–120 horsepower at the crank, bringing the Impala SS from 303 HP to around 400–420 HP, with torque climbing from 323 lb-ft to over 400 lb-ft. Despite the factory backing, the kit is classified as a performance accessory—not a warranty-covered GM option—and requires professional installation.

Installation Process and Considerations

Installing the GMPP kit is not a weekend driveway job for the average enthusiast. It involves removing the factory intake manifold, fuel rail, throttle body, and airbox, then mounting the supercharger and associated cooling systems. The coolant tank and heat exchanger require mounting in the front bumper area, requiring cutting or modifying the lower grille. Electrical work includes wiring the intercooler pump and fuel pump controller. The factory PCM must be flashed with GMPP’s calibration, which raises the boost target to around 7–8 psi. Professional installation at a speed shop or dealership can range from $800 to $1,500 depending on labor rates and location. DIY installation is possible for experienced mechanics but carries risks: incorrect belt routing, coolant leaks, or improper clamp torque can lead to poor performance or engine damage. The kit requires no internal engine modifications (no cam, no forged pistons), but many owners opt to upgrade the transmission cooler and add an auxiliary oil cooler for additional safety.

Installation Cost Breakdown

  • GMPP Supercharger Kit: $2,500
  • Professional Installation: $800 – $1,500
  • Custom Tune (if not using GM calibration): $300 – $500 (some owners report that the GM tune is overly conservative, so they pay a local tuner to refine it)
  • Miscellaneous (fluids, hoses, clamps, coolers): $150 – $400
  • Total out-of-pocket: Approximately $3,750 – $4,900

Given that a clean Impala SS can be had for $8,000–$12,000, this represents a significant fraction of the car’s value—but for dedicated enthusiasts, the performance uplift is often deemed worthwhile.

Real Owner Experiences

To cut through the marketing, we aggregated feedback from multiple Impala SS enthusiast forums (including ImpalaSuperForums.com and LS4Forums.com) and from owners who have logged tens of thousands of miles with the GMPP kit. The consensus is largely positive, but nuances emerge.

Positive Feedback

  • Dyno-proven power: “I saw 395 whp and 380 wtq on a Mustang dyno with only the kit, a cold air intake, and a 3.4-inch pulley upgrade. The car pulls hard from 3,000 to 6,500 rpm. It transforms the Impala from a quick sedan into a genuine sleeper.”
  • Daily drivability: “The GM tune is surprisingly refined. no surging, no weird idles. You can still drive it in traffic and get 22 MPG on the highway if you stay out of boost. My wife didn’t even notice anything different until I hit full throttle.”
  • OE-quality fitment: “The brackets and hoses all bolt up like GM designed it for the production line, because they sort of did. No cutting or welding needed for the main parts. The only tricky part is the coolant reservoir location.”
  • Resale value premium: “I sold my ’09 SS with 80k miles for $3,000 more than comparable non-supercharged cars. The buyer specifically wanted a GMPP-equipped car because it was ‘factoryish.’”

Negative Feedback

  • Installation complexity discouraged many: “I paid a shop $1,200 to install it. Then the tune was off—it kept throwing a P0171 code (lean bank 1). I ended up spending another $400 at a local dyno tuner to fix the fuel curve. The kit isn’t truly plug-and-play despite what GM claims.”
  • Heat soak on hot days: “After three consecutive pulls, the intercooler heat exchanger gets heat-soaked and IATs skyrocket above 140°F. The car pulls timing hard. You really need an upgraded heat exchanger and a larger coolant reservoir if you plan to track it or do any sustained hard driving.”
  • Belt slip at higher boost: “With the stock pulley, it’s fine. But if you drop to a 3.2-inch pulley for more boost, the belt slips even with a serpentine tensioner upgrade. Many of us switch to a 8-rib pulley kit to fix that—more money.”
  • Transmission durability concern: “The 4T65-EHD transaxle is already the weak link in the LS4 platform. Adding 100+ hp without a proper rebuild or at least a cooler and shift kit is asking for trouble. I grenaded my 2-3 clutches after 6,000 miles of hard driving.”
  • Not a true factory warranty: “GM says it’s a performance part, so if your engine or transmission fails, the warranty is voided. That’s a gamble at $3,500 total install cost.”

Mixed Reviews

  • Cost vs. aftermarket alternatives: “I could have bought a used Procharger or Vortech centrifugal supercharger kit for $2,000 and made 450 whp with a standalone tune. The GMPP kit is more expensive for less peak power, but it’s simpler and passes emissions visually better. It’s a trade-off.”
  • Power band preferences: “The M90 roots makes boost immediately off idle, so it feels faster on the street. But on the highway, a centrifugal blower pulls harder up top. If I did it again, I might choose a centrifugal for top-end rush.”
  • Long-term reliability: “I have 40,000 miles on my GMPP kit. Still runs great, but I’ve had to replace the intercooler pump twice—they’re cheaply made. Also, the harmonic damper on the LS4 can fail under boost loads, so I swapped to an aftermarket damper as a precaution.”

Cost-Benefit Analysis: Is $2,500+ Worth It?

At the entry price of $2,500, the GMPP kit is not the cheapest way to add 100 hp to an LS4 Impala. For context, a cam swap, headers, and a tune can yield 60–80 hp for under $1,500. A nitrous oxide kit costs $400–$800 but must be refilled. However, the supercharger offers instant, on-demand power with no bottle refills and no cam idle changes—a compelling proposition for daily drivers.

Financial Perspective

  • Resale value addition: As noted, some owners recover $2,000–$3,000 of the kit cost at resale. If you plan to keep the car for 3–5 years, the net cost is roughly $1,000–$1,500 per year for the upgrade.
  • Insurance premium: Disclose the modification; premiums may increase by $100–$200 per year.
  • Maintenance savings vs. other forced induction: Because the GMPP kit uses a standard Eaton M90, replacement parts (bearings, rotors) are widely available and relatively cheap compared to proprietary supercharger units.

Performance per Dollar

Considering total install cost ($3,750–$4,900), the cost per horsepower gain (assuming 100 whp) is $37.50–$49.00 per whp. That’s competitive with entry-level centrifugal kits but higher than a turbo build (if you can fabricate). The trade-off is simplicity: no oil lines, no fabrication, and a CARB EO number for many states (check local emissions laws).

What the Investment Buys You

  • Driving enjoyment: The linear boost curve of a Roots blower makes the Impala SS feel genuinely fast at any RPM. Many owners describe it as “how the car should have come from the factory.”
  • Reliability with the right supporting mods: If you budget for a transmission cooler, upgraded heat exchanger, and a custom tune, the kit is reliable for 50k+ miles.
  • Bragging rights and community respect: Among Impala SS owners, a GMPP kit is a well-known, respected upgrade that holds its value in the enthusiast market.

Alternatives to the GMPP Supercharger Kit

Before committing, consider these alternatives:

  • Centrifugal supercharger kits (Procharger, Vortech): Typically $3,000–$4,500 complete, requiring more fabrication but capable of 450+ whp. They are less visually integrated and may require custom tune support. Some owners prefer these for high-rpm track use.
  • Turbocharger setups: Custom turbo kits for the Impala SS exist (e.g., from ZZ Performance or local fabricators). They can produce 500+ whp but cost $5,000–$8,000 and require serious engine work (forged pistons, rods, etc.) to survive.
  • Naturally aspirated builds: A combination of ported LS4 heads, a larger cam (e.g., 224/230 .600 lift), long-tube headers, and a tune can yield 350–380 whp for $2,500–$3,500. This avoids supercharger weight and heat, but power delivery is milder and less flexible.
  • Nitrous oxide (wet shot): A simple 100-shot can provide similar peak power gains for under $1,000, but refills are costly and bottles need regular filling. Not ideal for daily consistent power.

Maintenance and Long-Term Reliability Considerations

Owning a supercharged LS4 Impala requires proactive maintenance:

  • Frequent oil changes: Use synthetic oil (0W-40 or 5W-30) and change every 3,000–4,000 miles due to increased heat and load.
  • Intercooler system upkeep: The coolant pump and heat exchanger should be inspected annually. Flush the intercooler loop every two years with distilled water and a corrosion inhibitor.
  • Transmission cooling: Install an auxiliary transmission cooler (e.g., B&M 70268) if not already done. The factory cooler can be overwhelmed.
  • Belt and pulley inspection: Check for belt wear and tension every 10,000 miles. Belt slip at high boost is common; upgrade to a wider belt kit if pursuing pulley changes.
  • Engine durability limits: The LS4 has cast pistons and a weak connecting rod ratio. Sustain boost over 8 psi reliably, but 12 psi requires forged internals. Most GMPP kits run 7–8 psi, which is acceptable.

Final Verdict: Is It Worth It?

After analyzing hundreds of owner reports and considering the mathematical value, the GMPP Supercharger Kit is worth it for a specific type of Impala SS enthusiast: someone who values OEM-like integration, daily drivability, and proven power without advanced fabrication. It is not the cheapest, nor the most powerful, but it offers a balanced package with strong support from the GMPP community and many online resources (see GMPerformanceParts.com for official documentation).

Buy the kit if: you want a reliable 100+ HP increase, keep the car for at least a few years, are willing to budget for professional installation and a transmission cooler, and appreciate the off-idle torque of a Roots supercharger.

Pass on the kit if: you are on a tight budget, plan to drag race with sticky tires, or want maximum power per dollar (go centrifugal or turbo).

Ultimately, the GMPP kit has earned its reputation as one of the best bolt-on upgrades for the Impala SS. It’s not perfect—heat soak, transmission fragility, and tuning subtleties are real concerns—but with proper preparation, it transforms a fast sedan into a true performance passenger car. As one owner put it: “The first time you floor it from a 40-mph roll and feel the surge, you’ll forget about the $2,500. That’s worth it.”