The Mercedes‑AMG A45 is already a benchmark in the hot‑hatch segment, packing an aggressive turbocharged engine and all‑wheel drive that make it a thrill on both road and track. Yet for owners who aren’t satisfied with “enough”, the path to genuinely eye‑watering power lies in a well‑engineered turbo upgrade. One of the most proven packages for pushing the M133 engine beyond its factory limits is the Wagner Tuning Stage 3 Turbo Kit. This comprehensive kit is designed to elevate your A45 from a respectable 381 hp (or 421 hp in the 45 S) to a reliable 420 hp + — and with the right supporting mods, even higher figures are within reach.

In this article, we’ll break down exactly what the Wagner Tuning Stage 3 kit includes, what it takes to install it, the real‑world performance gains you can expect, and the key considerations to keep in mind before you commit. By the end, you’ll know whether this upgrade is the right step for turning your A45 into a track‑ready powerhouse.

What Is the Wagner Tuning Stage 3 Turbo Kit?

Wagner Tuning is a German engineering company with a strong reputation in the European performance aftermarket, particularly for forced‑induction systems on Mercedes, BMW, Audi, and VW platforms. Their Stage 3 turbo kit for the A45 (W176, 2013‑2018) is a complete replacement of the factory turbocharger assembly, intercooler, and charge‑air plumbing. Unlike a simple “bolt‑on” turbo, the Stage 3 kit is a fully integrated system that addresses the engine’s airflow, cooling, and fuelling requirements simultaneously.

Based on extensive dyno testing and real‑world validation, the kit is engineered to deliver a minimum of 420 hp at the wheels when paired with a proper ECU calibration. Many owners report numbers closer to 450 hp with additional supporting modifications such as high‑flow catalytic converters or a cat‑back exhaust.

Core Components of the Kit

  • Larger turbocharger – The centrepiece is a hybrid or billet‑wheel turbo that flows significantly more air than the stock unit. Wagner uses precision‑machined compressor and turbine wheels with an enlarged housing to increase both mass airflow and boost pressure safely.
  • Upgraded intercooler – The intercooler core is considerably thicker and features cast aluminium end tanks with improved internal fin density. This reduces intake air temperatures (IAT) under sustained boost, which is critical for consistent power and knock prevention.
  • Enhanced charge‑air piping – All hoses and pipes between the turbo, intercooler, and throttle body are replaced with larger‑diameter silicone or aluminium pieces. This reduces pressure drop and virtually eliminates the “burst” failures common with factory plastic piping on high‑boost cars.
  • Re‑engineered intake and downpipe adapters – The kit includes proprietary flanges and couplers that allow the larger turbo to interface cleanly with the existing engine bay layout. Wastegate actuation is also improved for more precise boost control.
  • Gaskets, seals, and hardware – All necessary consumables are included, meaning you can install the kit without needing to source additional parts.

Critically, the kit is ECU‑tune ready. While Wagner provides base map files for many common tuning platforms (like EcuTek, PCMflash, or Bootmod3), the kit does not include a full tune – you will need a custom or off‑the‑shelf calibration from a reputable tuner who works with the A45 platform. Wagner Tuning works closely with several tuning houses worldwide to ensure their hardware and software are complementary.

Installation Process and Practical Considerations

Installing the Wagner Tuning Stage 3 kit is not a weekend DIY job for a beginner. The work requires mechanical competence, a well‑equipped workshop, and familiarity with turbocharged Mercedes engines. Below is an outline of the major steps, from preparation to final tuning.

Step 1: Preparation

  • Gather tools: socket set, torque wrench, pry bars, coolant bleed kit, scan tool for relearns.
  • Order all fluids (coolant, oil) and plan for an oil change after the initial break‑in.
  • Ensure the engine is cold and the battery is disconnected.

Step 2: Remove Stock Turbo and Ancillaries

  • Drain coolant and remove the radiator fan assembly if necessary.
  • Disconnect all hoses, electrical connectors, and the downpipe from the stock turbo.
  • Unbolt the turbocharger and lift it out from the top (or bottom, depending on AWD drivetrain configuration).
  • Remove the factory intercooler and charge pipes.

Step 3: Install New Components

  • Mount the new intercooler and secure it with the supplied brackets.
  • Position the new turbocharger, taking care to align the oil supply and return lines.
  • Attach the new charge‑air piping and tighten all clamps to specification.
  • Reconnect the coolant hoses, vacuum lines, and electrical connections.

Step 4: Refill and Prime

  • Refill with fresh coolant and high‑quality engine oil (SAE 5W‑40 is common for built engines).
  • Prime the turbo by cranking the engine with the fuel pump fuse removed (or via a dedicated priming procedure) to avoid dry startup.

Step 5: ECU Flashing and Road Test

  • Install the tuning software and flash the appropriate base calibration.
  • Check for boost leaks, loose connections, and unusual noises.
  • Perform a gentle break‑in of 200–300 miles followed by a dyno session for final adjustments.

“I had my Wagner Stage 3 kit installed by a specialist shop in three days. The car immediately felt different – spool is slightly later than stock, but the top‑end pull is insane. After a custom tune from [Tuner], I am seeing 435 whp on 93 octane. The car is now a weapon.” — A45 owner, AMG forum

If you are not confident performing the install yourself, budget between $1,500 and $2,500 in labour costs depending on the shop rate. Many tuners will bundle the installation, flash, and dyno tuning into a single package.

Performance Gains – Breaking Down the Numbers

Factory Mercedes‑AMG A45 models produce 360 hp (pre‑2015), 381 hp (2015‑2018), or 421 hp (45 S). The Wagner Stage 3 kit, when combined with a proper tune, raises peak output to 420–470 hp at the crank depending on fuel quality and supporting mods. On a dyno that reads in wheel horsepower, expect around 350–380 whp on a Mustang or Dynojet. This represents a 20–30% increase over stock.

Torque and Curve Shape

Equally important is the torque curve. The stock turbo runs out of steam above 5,500 rpm, but the Wagner kit sustains boost well past 6,500 rpm. Peak torque climbs from ~475 Nm to around 550–600 Nm, with a flatter plateau between 3,500‑5,500 rpm. This makes the car significantly faster in third‑gear pulls on highways and on track straights.

Throttle Response and Spool

A common concern with larger turbos is increased lag. Wagner Tuning has carefully matched the compressor and turbine sizes to keep lag minimal. Spool is about 300–400 rpm later than stock, meaning full boost arrives around 3,200 rpm instead of 2,800 rpm. For daily driving, this difference is barely noticeable; on track, the trade‑off in top‑end power is well worth it.

Comparison to Other Stage 3 Options

The market also includes kits from Pure Turbos, ATP, and ATP‑style hybrids, but Wagner’s integrated intercooler and piping set a higher standard for cooling capacity and build quality. Independent testing on the M133 engine shows that Wagner’s intercooler is one of the few that can keep IAT within 15 °F of ambient during repeated pulls. This directly translates to consistent power output and lower knock risk.

Driving Experience – From Street to Track

Owners who upgrade to the Stage 3 kit report a profound transformation in the A45’s character. The car becomes more aggressive, more urgent, and more rewarding to drive hard.

  • Acceleration: 0–60 mph times drop from the factory 4.2 seconds to the mid‑3‑second range on sticky tires. 60–130 mph times improve by several seconds.
  • In‑gear flexibility: The extra torque means you no longer need to downshift for overtaking – even in sixth gear the car pulls strongly from 50 mph.
  • Sound: The turbo itself introduces a distinct whistle under boost, while the upgraded piping and downpipe give a deeper, more aggressive exhaust note. Many owners pair the kit with a cat‑back exhaust for even more presence.
  • Track behaviour: On a circuit, the improved power band allows you to hold a gear longer, reducing shift frequency. The intercooler keeps IAT stable even after multiple hot laps, so you don’t experience the power fade common with stock cooling.

Key Considerations Before You Buy

While the Wagner Tuning Stage 3 kit is a proven upgrade, it is not a magic bullet. You must account for the following before committing.

Warranty and Insurance

Installing any performance turbo kit will void your factory powertrain warranty. Some dealers may flag the ECU tune even if you revert to stock parts. Check with your local dealership for potential warranty denial. Additionally, inform your insurance company; failure to disclose major power modifications can lead to denial of coverage in an accident.

Supporting Modifications

The kit is designed to work with a stock fuel system and uprated downpipe, but for maximum reliability and power you should consider:

  • High‑flow downpipe – Removes the restrictive factory cat and improves spool.
  • Cold air intake – Reduces intake restriction and cuts IAT further.
  • Larger injectors or HPFP upgrade – If aiming for 450 hp+ on ethanol blends.
  • Upgraded intercooler (included) – Already in the kit, but ensure it’s properly ducted.

Reliability and Maintenance

Running higher boost and power puts additional stress on the engine. The M133 has a forged crank and strong internals, but the pistons and rings are not indestructible. Regular oil changes with a high‑performance 5W‑40 every 3,000–5,000 miles are recommended. Also monitor boost pressure, lambda readings, and knock via a logging tool. Many tuners include a basic datalogging dashboard with the tune.

If you intend to track the car often, consider an oil cooler upgrade. The A45’s stock oil cooler is marginal for sustained track use even at stock power. Wagner Tuning offers an auxiliary oil cooler kit that pairs well with their Stage 3 turbo.

ECU Tuning – The Missing Piece

As mentioned, the hardware alone will not give you 420 hp. The ECU calibration is the key that unlocks the kit’s potential. Wagner Tuning supplies a base tune file that ensures safe operation, but for full power you will want a custom tune from a recognized A45 tuner such as:

  • Racing Dynamics – Known for aggressive but safe calibrations on the M133.
  • EcuTek – Many tuners use this platform for its robust logging and customer maps.
  • Bootmod3 – Gaining popularity for its OBD‑II flashing convenience.

A good tune will optimise timing, boost pressure, fuelling, and valve timing for your specific fuel quality (91/93/98 RON or ethanol blends). Expect to pay $500–$1,200 for a custom dyno tune plus the cost of the software licence.

Cost Breakdown and Value

The Wagner Tuning Stage 3 Turbo Kit typically retails for between $3,500 and $4,500 depending on the dealer and current exchange rates. When you factor in installation ($1,500–$2,500), tune ($600–$1,200), and supporting mods like a downpipe ($400–$800), the total investment is around $6,000–$9,000. For that cost you gain 80‑100 reliable horsepower and a far more capable car.

Compared to other Stage 3 options, Wagner’s kit offers superior cooling and a more complete package. For an owner who wants a turnkey solution without piecing together parts from multiple vendors, it is an excellent value.

External Resources

For further reading and to see real owner experiences, check these resources:

Final Thoughts

The Wagner Tuning Stage 3 Turbo Kit is one of the most complete and reliable ways to push your Mercedes‑AMG A45 beyond the 420‑horsepower mark. It is not a budget upgrade, but for those who value quality engineering, consistent cooling, and real‑world drivability, it delivers everything it promises. With proper installation, a competent tune, and a commitment to maintenance, your A45 can become a true street‑legal track monster that keeps pace with cars costing twice as much.

Whether you are aiming for weekend track days or simply want an exhilarating daily driver, the Wagner Stage 3 kit is a worthy investment. Just be prepared for the added maintenance, potential insurance implications, and the inevitable loss of traction when you put your foot down.