The Mercedes-Benz CLA45 AMG: A Platform for Serious Power

The Mercedes-Benz CLA45 AMG has always been a standout in the compact performance sedan segment. Its hand-built M133 engine, a turbocharged 2.0-liter inline-four, delivers an impressive 375 horsepower and 350 lb-ft of torque from the factory. But for owners who crave more, the aftermarket has answered. The HPA Power Kit is one of the most comprehensive packages available, reliably pushing this four-cylinder past the 500-horsepower threshold. This guide breaks down what the kit includes, what installation entails, and what it takes to live with a 500+ hp CLA45 AMG daily.

When you’re chasing that kind of output from a small-displacement engine, every component matters. Factory turbochargers, fuel systems, and intercoolers are designed for a specific power band and longevity target. Upgrading requires a systems-level approach, which is exactly what the HPA Power Kit delivers. Rather than a single bolt-on part, it’s a coordinated set of hardware and software that works in harmony to transform the driving character of your AMG.

What’s Included in the HPA Power Kit

The HPA Power Kit for the CLA45 AMG is not just a reflash; it’s a complete hardware and software bundle. Each component is chosen to address a bottleneck in the stock engine’s breathing and fueling capacity. Here’s a detailed breakdown of the key elements:

High-Performance Turbocharger

The factory turbocharger on the M133 is small and responsive, but it runs out of steam at higher boost pressures. HPA’s upgrade uses a larger compressor wheel and revised housing to flow significantly more air. This is the primary enabler of the 500+ hp target. The increased airflow is matched with a billet wheel that improves spool characteristics, reducing lag compared to older large-frame turbos.

Upgraded Intercooler

Compressing air generates heat, and hot air is less dense, robbing power. The stock intercooler is adequate for OEM boost levels, but with the HPA turbo pushing higher pressures, a larger, more efficient core is mandatory. HPA’s intercooler features bar-and-plate construction and increased frontal area, keeping intake air temperatures in check during hard pulls. Lower IATs mean consistent performance run after run.

Enhanced Fuel Injectors and High-Flow Fuel System

More air demands more fuel. The stock injectors and fuel pump reach their limits around 450-470 hp on the M133. HPA includes larger injectors (often 650cc or higher) and in some versions a supplemental fuel pump or higher-flowing fuel rail. This ensures the air-fuel ratio stays safe and rich under full throttle, preventing detonation and keeping cylinder temperatures manageable. Without this upgrade, fuel starvation can lead to catastrophic engine failure.

High-Flow Exhaust System

Getting air in is only half the equation. The CLA45 AMG’s factory exhaust is restrictive, especially the catalytic converters and the backpressure-oriented muffler. The HPA kit includes a full cat-back or downpipe-back exhaust with mandrel-bent tubing, a high-flow catalytic converter, and a free-flowing muffler. This reduces exhaust gas temperature and improves turbo spool, contributing to both power and a more aggressive sound.

Performance ECU Tune

All these hardware pieces are useless without a proper calibration. HPA provides a custom ECU tune (often via a handheld flash tool or by sending in your ECU) that adjusts boost pressure, fuel maps, ignition timing, and throttle response. The tune is optimized for the larger turbo and injectors while maintaining safety margins. It also raises the speed limiter and adjusts transmission shift points for the increased torque. This is where the magic happens—transforming raw potential into usable, reliable power.

Installation: What to Expect

Installing the HPA Power Kit is not a beginner-level job. It requires mechanical competence, specialty tools, and careful attention to torque specs and fluid levels. While some experienced DIYers can tackle it in a well-equipped garage over a weekend, most owners opt for professional installation at a reputable performance shop. The kit is designed to be a direct bolt-on for the CLA45 AMG (model years 2014-2019 for the M133 engine), but there are variations between facelift versions.

The basic installation steps involve:

  • Draining coolant and engine oil, then removing the front bumper and intercooler assembly to access the turbocharger.
  • Unbolting the factory turbocharger from the exhaust manifold and oil/water lines. The manifold itself is often replaced or ported to match the larger turbo’s flange.
  • Mounting the upgraded turbocharger with new gaskets and hardware. It’s critical to torque the bolts to factory spec to prevent exhaust leaks.
  • Installing the upgraded intercooler and charge pipes. Some kits include a cold-air intake to reduce restriction on the compressor inlet.
  • Replacing the fuel injectors. This is a delicate operation—the high-pressure fuel system must be depressurized, and the injectors seated correctly to avoid leaks.
  • Bolting on the exhaust system from the downpipe back. If the kit includes a downpipe, it will require removing the turbo-to-cat connection.
  • Refilling fluids, performing a leak check, and then flashing the ECU with the HPA tune using the provided cable and software.
  • Finally, a road test is essential to verify boost pressure, air-fuel ratios, and transmission adaptation.

Total labor time can range from 10 to 20 hours depending on the shop’s familiarity. It’s wise to plan for additional supporting modifications, such as a colder spark plug (one or two steps colder) and possibly an upgraded oil cooler if you intend to track the car.

Tuning for 500+ Horsepower: The Fine Print

The ECU tune is the heart of the HPA Power Kit. The M133 engine runs a Bosch MED17.7.5 ECU, which is encrypted and requires specialist tools to read and write. HPA provides a solution that typically involves either a bench flash (removing the ECU) or an OBD-II flash via a handheld flasher like the CMD Flash or Autotuner. The tune maps are developed on HPA’s own test vehicle and validated on engine dynos and track days.

Key tuning parameters adjusted include:

  • Boost pressure target: Increased from the stock ~26 psi to upwards of 30-32 psi depending on fuel quality and setup.
  • Fueling: Lambda targets are made richer (around 0.80-0.85 lambda) under full load to cool combustion. The larger injectors provide the headroom.
  • Ignition timing: Advanced slightly at low load for response, but pulled back under high boost to prevent knock. A knock sensor feedback loop is critical.
  • Throttle mapping: Aggressive tip-in for a more immediate response.
  • Transmission torque limits: The AMG Speedshift DCT 7-speed is robust but does have torque management tables that must be raised to accept the increased output. Without this, the transmission may slip or go into limp mode.

It is absolutely essential to use high-octane fuel—at least 93 octane (AKI) in the US, or 98 RON elsewhere. Lower octane will trigger knock, causing the ECU to pull timing and reduce power. For maximum output, many owners run a splash of ethanol (E30 or E85 blend) which offers additional octane and cooling. However, the HPA tune must be specifically calibrated for ethanol blends.

Post-Upgrade Driving Experience: More Than Numbers

Dyno sheets are one thing, but how does the car actually drive with 500+ hp? The CLA45 AMG’s all-wheel-drive system (4MATIC) is a huge asset here. In stock form, the car can feel a bit front-heavy under hard cornering. With the HPA kit, power is delivered more aggressively, and the AWD system will actively shift torque to the rear axle to manage traction. The result is a launch that pins you into the seat. 0-60 mph times drop from the factory 4.0 seconds to around 3.3-3.5 seconds with a proper launch control activation. Quarter-mile times go from the mid-12s into the high-11s or low-12s.

The engine note changes dramatically. The larger turbo whistles more audibly, and the free-flowing exhaust adds a deeper, more aggressive tone without being intolerably loud on the highway. Some kits include a valve-controlled exhaust that allows you to quiet things down for daily driving. Throttle response sharpens, but there is slightly more lag compared to the small factory turbo—peak boost arrives around 3500 rpm instead of 2500-3000. For spirited driving, keeping the revs above 3500 yields explosive acceleration.

Handling is also affected. The added weight of the larger intercooler and turbo is minimal, but the increase in power means the car’s chassis needs to be re-evaluated. Factory dampers and springs are calibrated for the stock power. Many owners pair the HPA kit with upgraded coilovers and a rear sway bar to reduce body roll and improve turn-in. The brakes also become a weak point; factory AMG brakes are decent, but repeated high-speed stops from 150+ mph will fade them. Upgraded pads, fluid, and possibly a big brake kit are recommended for track use.

Maintenance and Reliability Considerations

A 500+ hp CLA45 AMG is not a low-maintenance machine. The M133 engine is robust, but pushing it to double its original specific output per liter requires vigilance. Here are the critical maintenance practices for an HPA-equipped car:

  • Oil changes every 3,000-4,000 miles using a high-quality 5W-40 synthetic oil that meets MB229.51 specification. The turbocharger heavily stresses the oil, and heat cycles break down viscosity quickly.
  • Transmission fluid and filter change every 30,000 miles. The DCT clutches can slip if the fluid is degraded from high torque loads.
  • Spark plugs should be changed every 10,000 miles using a colder heat range (e.g., NGK 6510 gapped to 0.022 inches). The increased cylinder pressure can blow out the spark, causing misfires.
  • Inspect boost hoses and clamps regularly. Higher boost pressure can pop stock silicone couplers off their beads. Use reinforced T-bolt clamps for a secure fit.
  • Coolant system condition: The larger intercooler and increased heat load may require a higher-flow water pump or an auxiliary radiator. Monitor coolant temperatures with a P3 gauge or through the ECU via an OBD-II app.
  • Fuel system cleanliness: Running high-ethanol content fuels can cause corrosion in stock fuel lines. Use ethanol-compatible injectors and lines if planning E85 regularly. Also, replace the fuel filter at 20,000 miles.

Reliability depends heavily on the tune’s quality and the supporting mods. HPA has a strong reputation for durable tunes when the car is run on the recommended fuel and maintenance schedule. However, any 500+ hp four-cylinder will have reduced engine life compared to a stock car—expect to rebuild or replace the engine around 80,000-100,000 miles if you push it hard consistently. That’s the price of high specific output.

Comparing the HPA Power Kit to Other Options

HPA is not the only option for boosting a CLA45 AMG. Several other tuners offer similar packages: Renntech, Weistec, Eurocharged, and Pure Turbos each have their own kits. The HPA kit tends to be pricier (around $6,000-$8,000 for the full package installed, depending on options) but it is often considered the most complete and proven. Renntech provides a turnkey solution with a warranty for original owners, while Weistec focuses on larger turbos capable of 650+ hp with built engines. HPA strikes a balance between reliability and power for daily-driven street cars.

One major advantage of HPA is customer support. They have extensive experience with the M133 platform and offer remote tuning adjustments if you change fuel types or altitude. They also provide data logging tools to verify the car’s health after installation.

For those on a budget, a standalone ECU tune and a downpipe can yield ~430-450 hp for much less money. But to break the 500 hp barrier, the entire fuel and turbo system must be addressed—this is where HPA’s integrated kit shines.

Real-World Results and Owner Feedback

Owners who have installed the HPA Power Kit report consistent 500-520 whp on dynojet dynamometers using 93 octane. With an ethanol blend (E40), some have seen up to 570 whp. The torque curve is broad and flat, with over 450 lb-ft available from 4000 to 6500 rpm. The car pulls relentlessly to redline, a far cry from the stock engine that runs out of breath at around 6200 rpm. On the street, the power is addictive, but traction becomes an issue in the wet or on cold tires. The electronic stability control must be partially disabled to allow any wheel slip, which takes some getting used to.

Common owner praise includes the linear power delivery, the exhaust note without drone, and the ability to still achieve 25 mpg on the highway if driven gently. Common complaints focus on the increased interior noise (turbo spool and exhaust are more present), the cost, and the need for constant maintenance. A few owners have experienced boost leaks or failed intercooler welds, but these are rare and usually covered under HPA’s warranty.

For further reading, check out HPA Motorsports’ official site for product details, MBWorld CLA45 forums for owner testimonials, and Mercedes-AMG’s technical primer on the M133 engine architecture.

Summary: Is the HPA Power Kit Right for You?

Upgrading your CLA45 AMG with the HPA Power Kit to reach 500+ horsepower is a transformative experience. It requires significant investment—both financially and in terms of ongoing care—but the reward is a compact sedan that can embarrass much more powerful cars on the road and track. If you’re the type of owner who enjoys keeping a car properly sorted, who values the thrill of a borderline ridiculous amount of power in a small package, and who understands the importance of supporting mods, this kit is one of the best available.

If you simply want a fast daily driver without the headache of constant maintenance, a stage 1 tune and exhaust might suffice. But for those who crave the full potential of the M133, the HPA Power Kit delivers in spades.