Mercedes A45 S AMG W177: the M139 unmuzzled, the complete exhaust system guide

Your vehicle.

All our exhausts for this generation, version by version, are brought together on one page: Mercedes-AMG A45 / A35 W177 exhaust system.

The A45 W177 is the most powerful compact from Mercedes-AMG, and its engine is unlike any other four-cylinder. To choose its exhaust well, you need to know the two versions of the car, the way AMG designed the M139 and what the standard line does to its voice.

Models

Mercedes-AMG A45 4MATIC+ and A45 S 4MATIC+, A-Class type W177

Launch

July 2019, at the Goodwood Festival of Speed; model years 2020 to 2022 on the product page

Engine

M139: 2.0 litre inline four-cylinder, one twin-scroll turbo

Factory output

387 hp and 480 Nm (A45); 421 hp at 6,750 rpm and 500 Nm (A45 S)

Transmission

AMG SPEEDSHIFT DCT 8G, eight-speed dual-clutch

Drivetrain

4MATIC+ with AMG TORQUE CONTROL on the rear axle

Top speed

250 km/h for the A45, 270 km/h for the A45 S

Factory exhaust

A flap controlled by engine speed and load

One compact, two power outputs

Mercedes-AMG presented the W177-generation A45 on 4 July 2019, at the Goodwood Festival of Speed, alongside the CLA 45 S. The compact came in two versions from the start: the A45 4MATIC+ and the A45 S 4MATIC+, more powerful and better equipped. Depending on the market, one or both were offered, with deliveries starting at the end of 2019.

The Rog product page covers both versions for model years 2020 to 2022. An A45 from the very end of 2019, or one built after 2022, is simply checked by VIN, like every order, before manufacturing begins. The CLA 45 S, the earlier A45 W176 and the A35 each have their own product page.

387 or 421 hp: the two A45s

The base A45 develops 387 hp (285 kW) and 480 Nm. The A45 S rises to 421 hp (310 kW), reached at 6,750 rpm, and to 500 Nm available between 5,000 and 5,250 rpm; its engine revs up to 7,200 rpm. It goes from 0 to 100 km/h in 3.9 seconds and reaches 270 km/h, while the base version is limited to 250 km/h.

The progress over the previous generation is clear: maximum torque rises from 475 to 500 Nm. For a five-door compact, these figures put the A45 S on a level with much bigger sports cars, without taking anything away from its everyday use.

The bars below show, unchanged, the values published on the product page for each of the two versions.

Factory 387 hp version

Factory 421 hp version

Stage 2: published figures with the front section and an ECU remap carried out by a tuner.

The M139, an engine turned through 180 degrees

According to Mercedes-AMG, no production turbo four-cylinder delivers more power than the M139. Its distinctive feature is plain to see under the hood: the engine has been rotated 180 degrees about its vertical axis. The turbo and exhaust manifold are therefore at the rear, against the bulkhead, and the intake is at the front, which shortens the air's path.

The twin-scroll turbo runs up to 2.1 bar on the A45 S. For the first time at AMG, the compressor and turbine shafts spin on roller bearings, which benefits low-rev response. Each engine is assembled in Affalterbach on the "One Man, One Engine" principle: a single engine builder assembles it from start to finish.

DCT 8G, 4MATIC+ and Drift mode

Power goes through the AMG SPEEDSHIFT DCT 8G transmission, a dual-clutch with eight speeds, then through the fully variable 4MATIC+ all-wheel drive. At the rear, AMG TORQUE CONTROL distributes torque between the left and right wheels using two controlled clutches.

This distribution makes a Drift mode possible, standard on the A45 S and offered in the AMG DYNAMIC PLUS package on the base version. It is activated in Race program, with stability control off and the transmission in manual mode, using the steering wheel paddles. For the exhaust, nothing changes from one drivetrain to the other: the same Rog line serves both A45s.

Six AMG Dynamic Select programs

The driver sets the behaviour of the A45 with AMG Dynamic Select: Slippery, Comfort, Sport, Sport+, Individual and Race. The Race program is standard on the A45 S; on the base version, it comes with the AMG DYNAMIC PLUS package. Each program changes throttle response, gear changes and sound.

On the exhaust side, the car leaves Mercedes-AMG with a flap whose opening depends on engine speed and load. In Slippery, Comfort and Sport, the sound stays measured; it grows fuller in the sportiest programs, and Individual mode lets you choose between two sound settings.

What holds back the voice of the M139

A 421 hp four-cylinder that revs to 7,200 rpm has plenty to sing about. On the standard compact, though, the rear muffler and the flap management keep it within a very polished sound envelope, designed for an A-Class parked in town. The engine is mainly heard when pushed, and even then with restraint.

With the flaps open, the Rog line gives it a full, angry tone, a frank rev climb up to the limiter, then crackles when you lift off. Once the flaps are closed, the A45 returns to a voice close to the one it was delivered with, so you can come home late without waking the street.

Your AMG flaps or the Rog remote

The product page offers two ways to control the flaps. With the Factory option, the Rog line arrives with the mounting point of the factory flap: your garage refits it there, and the AMG Dynamic Select programs keep deciding its opening, as before.

With the Rog option, the flaps are delivered fitted, with a remote. Open, they stay open; closed, they stay closed, whether you drive in Comfort or in Race. It is the solution for those who want a discreet M139 in Sport+, or on the contrary a full voice in Comfort, in town as on a country road.

Stainless steel or titanium, straight pipe or resonator

304 stainless steel resists salt and damp without trouble; titanium weighs about 40% less for the same design and comes in three finishes, brushed, gold or purple. On a compact as lively as the A45, every kilo removed at the rear is felt in the weight transfers, and titanium gives the four-cylinder a more metallic note at high revs.

For character, there are two choices at the same price. The straight pipe lets through the dry scream of the M139 and its pops when you lift off; the resonator gives it a rounder and slightly softer voice, which suits an A45 that also serves as an everyday car. Rog tips can be chosen in chrome, gloss black or blued titanium, or not at all.

The optional downpipe, on the bulkhead side

Because the engine is turned around, its turbo sits on the bulkhead side, and that is where the downpipe starts, with its catalytic converter. On the product page, it appears under the name "Manifold": in 200 cells, the emissions control stays in place; the 100-cell version opens the gas passage further, with an acceptance that depends on the car and the country; the catalyst-free version is intended for the track.

Without a remap, the downpipe adds voice and saves a little weight, but not a single horsepower. The power figures published on the product page assume this front section and a map redone by a tuner. Rog makes your line to your VIN; your garage fits it without welding or cutting.

Configure your exhaust.

How the exhaust is put together

On the A45 W177, the Rog line starts at the downpipe connection and runs to the tips: pipes, mufflers and flaps. The downpipe, which comes down from the turbo placed against the bulkhead and carries the catalytic converter, forms the front section; the product page offers it as an option under the name "Manifold".

Each choice explained in detail, from sound to material: How to configure your exhaust.

Three recommended configurations.

• The everyday compact

  • Stainless steel
  • No manifold
  • Resonator
  • Factory valves

  For an A45 that also does the shopping and the office run: the M139 gains a real voice, the factory front section stays in place, the resonator rounds off its scream and AMG Dynamic Select keeps controlling the flap.

  View this configuration

• Sunday country roads

  • Titanium
  • 200-cell sports catalytic converter
  • Straight pipe
  • Rog remote

  For an A45 S taken out early in the morning on winding roads: 200-cell downpipe to keep the emissions control and gain presence, lighter titanium, and flaps opened at the touch of a button, even in Comfort.

  View this configuration

• Race program, on track

  • Titanium
  • Decat
  • Straight pipe
  • Rog remote

  For an A45 S that strings together track sessions: catalyst-free downpipe reserved for circuit use, straight pipe to hear the M139 up to 7,200 rpm, and flaps left open all day.

  View this configuration

From order to fitting.

VIN, manufacture, delivery, fitting and warranty, step by step

Questions.

Further reading.

• All our lines for the Mercedes A-Class W177
• Mercedes-AMG A45 W176 guide, the previous generation
• Mercedes-AMG CLA 45 S C118 guide, the same M139
• Mercedes-AMG A35 W177 guide