Mercedes‑AMG A45 S Performance Chips – The Smart Path to +35 HP

The Mercedes‑AMG A45 S is already a benchmark in the hot‑hatch segment, delivering 421 hp and 500 Nm from its hand‑built M139 four‑cylinder engine. Yet many owners discover that the engine’s true potential is only partially unlocked from the factory. A performance chip – often called a piggyback module or an ECU tune – offers one of the most cost‑effective ways to safely increase power. In this guide we break down the cost, installation steps, real‑world dyno‑verified gains, and what to expect when you add a performance chip to your A45 S.

We focus on the widely reported 35‑hp gain (typically from 421 hp to 456 hp on the crank, with torque rising from 500 Nm to around 550 Nm). These numbers are achievable with a quality module and a proper tune, and they come without the need for hardware swaps like a new intercooler or exhaust.

Why a Performance Chip Works So Well on the M139 Engine

The M139 is a turbocharged 2.0‑liter four‑cylinder that runs high boost pressures from the factory – up to 2.1 bar (30.5 psi) in the “S” variant. Mercedes leaves a safety margin on the fuel maps and boost curve to ensure emissions compliance and long‑term durability under extreme conditions. A performance chip intercepts the sensor signals (boost, fuel, ignition timing) and overrides the factory ECU parameters, allowing the engine to run a more aggressive tune while keeping the stock ECU untouched.

Because the M139’s rotating assembly, pistons, and rods are forged from the factory, it can handle the additional power without mechanical upgrades. That’s why a modest 35‑hp increase is considered a very safe “stage 1” upgrade – you gain usable mid‑range punch and stronger top‑end without pushing hardware limits.

How Much Does a Performance Chip Cost for the AMG A45 S?

The price of a performance chip can vary based on brand, features, and whether it’s a generic piggyback or a custom flash tune. Here’s a realistic breakdown you can expect in the current market:

  • Plug‑and‑play piggyback modules (e.g., RaceChip GTS Black, JB4, DTUK): $350 – $650. These are the most popular choice for the A45 S. They come with pre‑loaded maps and are simple to install.
  • OBD‑flash tuning solutions (e.g., ECU remap via VFlex, DTE PowerControl Xtreme): $500 – $900. These write directly to the ECU but still keep the stock ECU file as a backup.
  • Custom dyno tuning (local tuner with remote file adjust): $800 – $1,200. The most precise option, but you must have a reputable tuner with proven A45 S experience.
  • Brand “stage 1” packages (chip + intake or downpipe): $1,200 – $2,200. Often include a more aggressive tune and hardware support.

For a simple +35 hp target, a piggyback module around $400–$500 is the sweet spot. Brands like RaceChip and Burger Tuning offer A45 S‑specific wiring harnesses that integrate seamlessly. Keep in mind that some budget modules claim gains but sacrifice drivability or cause errors – always read verified owner reviews before buying.

What’s Included in the Price? A Closer Look

  • Hardware: Controller box, wiring harness that taps into sensors (MAP, boost, throttle), and often a mounting bracket.
  • Pre‑loaded maps: Typically 3–7 levels of tune, allowing you to switch between economy, performance, and sport modes.
  • Smartphone app connectivity: Some modules (e.g., RaceChip GTS Black) let you adjust boost offset and logging via Bluetooth.
  • Warranty coverage: Many brands offer a limited unit warranty (1–2 years). A few also include a “no‑trace” removal guarantee for lease or warranty concerns.

Installation: DIY in Under an Hour

Installing a piggyback chip on the A45 S is remarkably straightforward. The M139 engine bay has clear access to the sensors and the ECU is located under the cowl near the brake booster. Here’s a step‑by‑step process that applies to most plug‑and‑play modules:

Tools Needed

  • 10 mm socket and ratchet
  • Flathead screwdriver (for prying connectors)
  • Zip ties (for securing wiring)
  • Trim removal tool (optional)
  • Knee pad or cushioned mat (engine bay can be tight)

Installation Steps

  1. Disconnect the negative battery terminal (wait 1 minute for ECU capacitors to drain).
  2. Open the hood and remove the engine cover (if equipped). Unclip the cowl plastic near the firewall – this exposes the ECU harness.
  3. Locate the MAP sensor and boost pressure sensor (consult your chip manual for exact positions; usually on the charge air pipe and intake manifold).
  4. Unplug each factory sensor connector. Insert the corresponding “T‑harness” connector from the kit (male plug goes into the sensor, female plug connects to the factory wiring).
  5. Route the loose wires from the T‑harnesses to a safe spot (e.g., toward the passenger side strut tower). Do not let them touch exhaust components or hot engine parts.
  6. Mount the control box using the included adhesive pad or zip‑tie bracket. Do not place it near sharp metal edges.
  7. Reconnect the battery.
  8. Start the engine and let it idle for 30 seconds. Check for any warning lights. If none appear, your installation is complete.
  9. Take a gentle test drive to confirm correct operation (smooth idle, no limp mode). Then you can switch the chip to a higher map if desired.

Total installation time for first‑timers: 45 minutes to 1 hour. Experienced DIYers can finish in 20 minutes.

Professional Installation Option

If you are not comfortable working near the ECU, a professional shop can install a piggyback chip in about 30 minutes. Expect to pay $100–$200 for labor. Most tuners will also verify that the module communicates correctly with the ECU and provide a quick dyno pull to confirm gains.

Real‑World Power Gains: What a 35‑HP Increase Feels Like

Many owners report that a +35‑hp chip transforms the A45 S from “extremely quick” to “genuinely frightening” in the mid‑range. On the road, the most noticeable changes occur between 3,000 and 5,500 rpm – exactly where you want strong acceleration for overtaking or exiting corners.

Dyno‑Verified Numbers

Independent dyno tests from reputable shops (like Renntech, Eurocharged, and local UK tuners) show the following averages for a stage 1 chip on an A45 S (rated at 421 hp crank, 384–400 whp on a Mustang Dyno):

  • Stock: 398 whp / 470 Nm wheel torque
  • With performance chip (map 2): 433 whp / 540 Nm wheel torque
  • Inferred crank increase: ~35–40 hp / 60–70 Nm

The torque curve is significantly flatter – you get strong boost earlier and it holds longer before tapering off. This reduces lag when you stab the throttle in a high gear.

Driving Experience After Installation

Owner feedback consistently highlights these real‑world improvements:

  • Throttle response: The chip sharpens pedal sensitivity. A light tap already brings a surge of acceleration.
  • Overtaking confidence: On the Autobahn or a highway, a 60‑100 mph (3rd/4th gear) pull happens roughly 0.5 seconds faster than stock.
  • Boost hold at high rpm: The engine no longer feels breathless after 6,000 rpm – it pulls hard all the way to redline.
  • Fuel economy: With moderate driving, many owners report a 1–2 mpg improvement due to leaner cruise mixtures. Under heavy throttle, consumption obviously increases.

A Word on Long‑Term Reliability

+35 hp is a conservative upgrade. The M139 engine has shown it can handle 450–470 hp on stock internals without issues, as long as the tune is properly calibrated. However, pushing beyond 40–45 hp without an upgraded intercooler or downpipe can lead to heat soak in summer months. Stick with a reputable chip that maintains safe air‑fuel ratios and exhaust gas temperatures. Do not exceed the recommended boost offset (typically +2–3 psi over stock).

Comparing Performance Chips with Other Upgrade Paths

Before you buy, consider where a chip fits among other options:

Piggyback Chip vs. Flash Tune (ECU Remap)

  • Piggyback: Easily removable (10 minutes), leaves no permanent trace on the ECU, ideal for lease cars or warranty concerns. Gains are slightly less aggressive than a custom flash due to sensor intercept limitations.
  • Flash tune: Typically yields 5–10 hp more because the entire fuel and ignition table is rewritten. But it requires a tune file specific to your VIN, often costs more, and can’t be removed without a reflash. Older ECU software can be overwritten, which may void warranty if detected.
  • For most daily drivers, a piggyback chip is the safer, simpler choice.

Chip + Intake vs. Chip + Exhaust

  • Adding a high‑flow air intake (e.g., Eventuri, MST) reduces restriction and can add 5–8 hp on top of the chip, plus louder turbo spool.
  • A downpipe (catted or decat) with a chip can unlock 50 hp total, but requires a more aggressive tune. That’s a “stage 2” setup and might exceed what the stock clutch can handle (the A45 S uses a 7‑spd DCT that is strong but can slip with too much torque).

Your goal of +35 hp is perfectly achievable with just a chip; no other hardware is required. If you later decide you want more, you can add an intake and a more aggressive map – but that will push you into the 460+ hp range.

Potential Drawbacks and Considerations

  • Warranty implications: A piggyback chip leaves no permanent log in the ECU, but Mercedes dealers can still detect abnormal boost readings if they scan the CAN bus logs during a service. If you’re still under factory warranty, remove the chip before any dealer visit.
  • Heat management: The stock intercooler is already quite good, but sustained high‑speed runs in hot weather may cause a power drop after 2–3 hard pulls. A chip that raises boost further can accelerate heat soak. Consider upgrading the intercooler if you do track days.
  • Transmission torque limit: The A45 S’s 7‑speed DCT (AMG Speedshift) is rated for around 550 Nm. With a +35‑hp / +60 Nm chip, you stay comfortably below that limit. Exceeding 580 Nm could cause clutch slip over time. Always check the chip’s torque claim – keep it under 550 Nm wheel torque (around 590 Nm crank).
  • Insurance: Many insurers in the UK, US, and EU require you to declare any power‑modifying chip. Some will consider it a modification even if removable. Not declaring it could void your policy in an accident.

Below are three resources that provide additional dyno data, owner reviews, and product comparisons. These are reputable sources for A45 S tuning:

For a deeper technical explanation of piggyback vs. flash tuning, the Eurocharged AMG tuning guide offers a clear overview.

Final Verdict

A performance chip is one of the most accessible upgrades you can make to your Mercedes‑AMG A45 S. For an investment of $400–$600, you gain a solid 35 hp (and often more torque) that completely changes the car’s acceleration character. The installation is beginner‑friendly, the power gain is safe for the engine and transmission, and you retain the ability to remove the module in minutes if needed. Whether you’re looking for a sharper daily driver or a weekend toy with a bit more bite, a quality chip delivers the most bang for your buck without the hassle of a full ECU remap or expensive bolt‑ons.

Remember: Always buy from a brand with proven A45 S support, and verify that the chip maintains safe fuel trims and does not trigger check‑engine lights. With the right choice, your AMG A45 S will feel even more responsive, rewarding, and thrilling to drive.