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Mercedes-AMG A45 S W177Stage 1 to Stage 4 tuning guide

The A45 S has the M139, the most powerful four-cylinder Mercedes has put in a production car, and the CLA45 S and GLA45 S share it. Published Stage 1 figures range from about 450 to 510 hp. Two control units matter as much as the tune: the engine computer must be unlocked first, and a separate unit called the CPC holds torque limits that can cap an engine tune.

Years
2019– (facelift 2023)
Engine
2.0 turbo four M139
Gearbox
AMG SPEEDSHIFT DCT 8G dual-clutch
Stock power (EU)
421 PS / 500 Nm
White Mercedes-AMG A45 S W177 with the Panamericana grille, parked on a rooftop

Power by stage

Stage 1 to 3 are the tuners' and turbo makers' own published figures; European tuners quote PS (1 PS is about 0.99 hp). Stage 4 is a thin community range, because few built-engine results are published. Real results depend on fuel, weather and the individual car.

Stock421 hp
Stage 1450–510 hp Stage 2470–520 hp Stage 3525–600 hp Stage 4600–650+ hp

Names with an arrow go straight to that part's product page for this car. Names in a dashed outline are other brands that make the part; exact links for them are being added.

1

Software only

+29 to +89 hp

Flash tunes need the engine computer unlocked first: Weistec says every car needs it, and Posaidon says it depends on the model year. The second limit is the CPC, a separate control unit that holds torque limits and the speed limiter; EST says a new, unused CPC coded to your car is the only safe way to lift those limits. Plug-in modules from RENNtech, RaceChip and DTE leave the factory software alone.

Typical cost: $1,499–$2,580 (Eurocharged, Weistec, RENNtech); gearbox tune $1,000 more; RaceChip €609; EST with a new CPC £1,550 including VAT.List prices, Sept 2026, before shipping, import tax and fitting.

Stage 1 tunes compared

TuneFuelClaimed powerClaimed torqueNotes
Weistec W.1Premium (no octane given)510 hp490 lb-ft+125 hp over Weistec's own stock figure; ECU unlock sold separately
RENNtech Power Module—490 hp398 lb-ftPlug-in module; a bypass plug returns the car to stock
RaceChip GTS 5 Black—490 PS540 NmPlug-in module (+69 PS / +40 Nm)
EST Stage 1 Full Solution99 RON460–480 hp560–620 NmIncludes a new CPC plus engine and gearbox tunes
mcchip-dkr Stage 1—470 PS580 NmFind the car in the tuner's database
Posaidon 46598 RON465 PS560 NmSoftware only; road approval not included unless stated
Eurocharged Stage 1—450 hp406 lb-ftWorks with an intake and a cat-back exhaust
Brabus PowerXtra B45-450—450 hp550 NmFigure from an authorised Brabus retailer; Brabus' own page is gone
DTE PowerControl RX—+49 PS+94 NmPlug-in module

Recommended with Stage 1

  • Engine computer unlock flash tunes WeistecPosaidon

    Needed before a flash tune; plug-in modules don't need it.

  • New CPC or CPC tune recommended ESTWeistecEurocharged

    Without it, the CPC's torque limiters can hold back an engine tune.

  • Gearbox (TCU) tune optional Weistec 8G-DCT TCU tuneESTEurocharged

    No maker says it's required at Stage 1. Weistec sells it for higher torque limits, and EST includes it to avoid clutch slip.

Before you buyIn Israel only 95 and 98 octane are sold: Posaidon's figures are on 98, and EST's are on 99 RON. Mercedes has also issued a service bulletin on broken valve springs that covers all M139 engines; it isn't caused by tuning, but ask whether it applies to your car first.
2

Intake, downpipe and exhaust

+49 to +99 hp

Stage 2 adds a downpipe and an intake, with a file written for them. On European cars the downpipe is the hard part, because it sits in front of the particulate filter (OPF/GPF): many downpipes bypass it, and those are for off-road use only. Later W177s also have an exhaust-temperature sensor in the downpipe, so buy the version that matches your car.

Typical cost: Weistec downpipe $899 or Milltek £990; water-methanol kit $1,600; EST Stage 2 £2,150–£3,750.List prices, Sept 2026, before shipping, import tax and fitting.

Stage 2 packages compared

PackageFuelClaimed powerClaimed torqueRequired hardware
EST Stage 299 RON490–520 hp620–700 NmEST x Cobra sports-cat downpipe, new CPC, engine and gearbox tunes
mcchip-dkr Stage 2—500 PS590 NmHardware not listed in the database entry
Eurocharged Stage 2—470 hp420 lb-ftIntake, downpipe and cat-back; sold for off-road use
Weistec W.2Premium+145 hp+179 lb-ftRace exhaust; gains are over Weistec's own stock figure

Parts list

Before you buyDownpipes without a catalyst or particulate filter fail inspection, and Weistec says its tune is not legal on cars covered by emissions laws. Keep the original parts.
3

Hybrid turbo

525–600 hp

Stage 3 upgrades the factory turbo, usually as a hybrid built on the original. Posaidon's RS525 claims 525 PS on 98 octane and can come with German road approval. EST, MACHGRADE and Weistec claim 545 to 600 hp, but all say fuel, cooling and a custom tune must come with the turbo.

Typical cost: hybrid turbos $2,999 (Weistec) or €1,470–€4,499 before VAT (TTE, MACHGRADE); EST570 £6,995–£8,550.List prices, Sept 2026, before shipping, import tax and fitting.

Turbo upgrades compared

KitFuelClaimed powerClaimed torqueNotes
Posaidon RS52598 RON525 PS600 NmSoftware and hardware; German road approval available
EST570—545–570 hp640–680 NmHybrid turbo, full intake, downpipe and charge-cooler kit
MACHGRADE 550 / 600—550 / 600 hp—The 600 needs a bigger turbine side and new oil and coolant lines
Weistec W.3—590 hp—Rebuild of your own turbo; custom tuning required

Parts list

  • Hybrid turbo required MACHGRADE M139 turboTTE560 turboPosaidonWeistecMuchBoost

    Sold with, or tuned for, a file written for that turbo.

  • Gearbox tune and new CPC required WeistecEST

    More torque needs higher gearbox limits and a CPC that doesn't cut it back.

  • Charge-cooler upgrade required EST

    EST lists its charge-cooler kit as the minimum for EST570; owners in hot climates report heat soak on the factory cooling.

Before you buyBudget for the full package: turbo, fuel, cooling, gearbox software and labour. Posaidon warns that warranty, insurance and road approval can be lost, and it gives no warranty for damage from the tune.
4

Built engine

600–650+ hp

Few built-engine M139 results are published, so this is a thin community range. The biggest turbo claims stop at about 590–600 hp (Weistec W.3 and MACHGRADE 600), and forged pistons and rods are sold for Stage 3 and racing builds. Owners on a UK forum say that 600 hp and up works on the stock engine internals, but that about 700 on the stock gearbox clutches won't last.

Parts list

  • Forged pistons and rods required IRP forged pistons and rods

    Sold for Stage 3 builds and dedicated racing use.

  • Bigger turbo and fuel system required MACHGRADEWeistec

    With the fuel and cooling upgrades the turbo maker specifies.

  • Gearbox clutches and cooling required WeistecEST

    The dual-clutch gearbox is the limit at this power.

Before you buyStage 4 is an engine build, not a bolt-on. Choose one shop to build, tune and stand behind the whole package.

Questions to ask the shop

  1. Does my engine computer need an unlock, how is it done, and what does it cost?
  2. Do you supply a new CPC? Without one, are the torque limits still active?
  3. Is a gearbox (TCU) tune included, and what torque does it allow?
  4. Which fuel is the file built for (95, 98 or 99 RON, or E85), and is there a safe map for the fuel I can buy?
  5. Do you log intake temperature and timing on hot, repeated pulls, and how do you deal with heat soak?
  6. Is the downpipe or particulate-filter work legal for inspection here, and what happens to my warranty?