As an introduction to different tuning stages I thought of a piece that would cover things broadly and then an individual piece for each level describing perhaps what it would entail for different cars and etc, if it is too long winded please jump to the TL;DR section below.

This is the introduction to the tuning stages vernacular. In general many people describe various tuning stages, and while this may not constitute a specific definition this does aide in communication amongst similar minded people.

I am sure a strong epistemological argument can be made that these stages are meaningless and etc, but in practical measures this is what the various tuning stages implies for late model bi-turbo Mercedes Benz vehicles. This holds true currently, but it may evolve over time as different driveline technologies are employed. Which is a different rabbit hole for a different post.

And in particular tuning stages helps with describing the type of tune you want from a tuner. Stage 1 tune from most tuners means something different than Stage 2 and Stage 3. Not all tuners use this but many do. Let’s dive in.

TL;DR

Stage 1

Stock hardware. Premium fuel (91–93). Calibrated for reliability and repeatable gains.

No permanent mods
Great daily drivability
Often OBD-flashable

Browse Stage 1

Stage 2

Supporting bolt-ons (e.g., downpipes, higher-flow intakes, better cooling).

Higher load targets & heat management
Best for spirited use / track days
OBD or bench depending on platform

Browse Stage 2

Stage 3

Upgraded turbos / fueling. Custom calibration around specific hardware & fuels (E-mixes).

Hardware + tune are a matched set
Requires datalogs and iteration
Bench or in-person recommended

Talk to a Calibrator

Stage 1 Tuning Definition

- No Cutting or Hardware Modifications to Car
- Any Software Calibrations or piggy back systems
- Mods like air intakes that can go back to stock quickly

Approximately 60hp-130hp gain from ECU remap/tune, air box/filter.

Stage 1 tune often employs an ECU tune, an airbox upgrade as needed (risers, UPD kit, ROW box) with better filters. Some people also will do exhaust in stage 1.

Although many tuners put this together and describe it as stage 1. Adding airbox risers, filters, and deleting resonators/mid-exhaust should result in 23-35 at wheel hp according to UPD and other dyno runs for such engines as the m278.

The ECU tune, or remapping will try to optimize the engine based on generic information, or specific information. Increasing pressure and boost the ECU tunes can improve HP by a fairly large amount. For example AMS performance, some say Renntech, and OE try to deliver 585 crank hp from the ECU tune on a M278 which is at stock likely 450-460hp although rated by mercedes at the crank at 402 in some applications.

Stage 2 Tuning Definition Hardware Modifications

Hardware modifications requiring cutting, welding, drilling into car
Hardware modifications that are not easily reversed
Long Tube Headers, Hi Flow Cats + Stage 1 type mods
Water Methanol Injection (a true/pure WMI tune would be stage 3 most people do not run those tunes due to very high risk without water-methanol)

More than 50hp gained from turbo back pipes (2 parts), mid resonators, ECU Remap/tune

While stage 1 may include exhaust, in stage 2 exhaust is 100% addressed. The turbo downtubes are replaced and often the cats are replaced as well. This can be done in two parts and some manufactures do sell that way. Although the turbo back cat delete, for a race car or as local laws permit, can be fabricated and installed at an exhaust shop for approximately $200 a piece so $400-500 is a fair price while shipped it can run upward of $1000.

This stage 2 tune is a difference because it will throw codes without some modification back to stock if the stock ECU is used. While Stage 1 tuning can be completely reversible, Stage 2 will require modification to return back to the stock ECU.

The stage 2 tune removes the CEL when these “primary” cats are removed and may also change the tune based on the idea that the cats are removed. Expect a gain of >40 awhp for an M278.

There are two different ways parts, one is a turbo back which will improve restrictions and produce a good power gain of 30-40hp. This part connects to a cat and 02 sensor, this part can be replaced separately at a muffler shop for off road use or replaced with upgraded higher flow cats. This part costs about $200 per side.

Some people may also upgrade cooling at this point.

Stage 3 Tuning Definition – Changes to Boost

- Adding or upgrading existing turbo system
- “Big turbos”, “Hybrid turbos”
- Changing to bigger fuel injectors adding an HPFP
- These mods require changes to the ECU to continue to run well and they require more intricate ECU tuning
- From a tuner perspective this is a harder lift and the tunes cost more
  - If you have those options above and want a tune please ask for a stage 3 tune price from your tuner
- Stage 3 tuning requires datalogging and the longer you can leave your car with the tuner the better the results

Approximately >70hp-300hp gained from improving turbos & methanol.

Stage 3 tuning takes the physical mods beyond the mere unbolting (on many Mercedes) of the cats, and physically modifies the Turbos. Mercedes choose a design of turbos that does not actually maximize power, but provides a nice balance of drivability, emissions, efficiency, luxury, and power. AMG and Brabus further optimize that balance toward power.

However, there are great amounts of power that can be gained by changing or upgrading the turbos which may change the drivability. As you add more turbo power much of the power is from boost which requires a certain amount of exhaust pressure so the power delivery is increasingly non-linear. A part of this stage will be modifications to support the additional power delivery, including swapping to AMG style fuel delivery. Many will also upgrade the brakes at this point.

Billet Turbos

turbo impeller

Billet turbos take the stock turbo application and modify them, and add different turbo rotors that are manufactured to much tighter tolerances. Combined with an ECU change based on individual pulls, an m278 engine should be able to achieve 600 awhp with such big turbo hybrid system. If you upgrade the HPFP you can get even more power.

Turbo Swap / Better Turbos

M157 Turbos can bolt up to m278 — These beautiful M157 Turbos are for sale on MBWorld right now and swap directly to M278

M278 engines can use M157 turbos they bolt up completely and can be had for $1500-3000, or you can hybrid many M278 turbos to be bigger the M157 turbos. This is slightly different than just changing the wheel and its geometry as the form factors are precision CNC on both wheels to support higher horsepower.

Check out our boost section here. On MBWorld thread “Build the most powerful CLS550” OP went for bigger hybrid turbos before going and building completely custom turbo setup with bigger turbos.

Weistec Turbo Upgrade for M157 Delivers 1000hp — Weistec Turbo Upgrade for M157 Delivers >1000hp

Weistec sells aftermarket turbos for several mercedes applications delivering immense power. As you approach 800-1000hp in an M157 Weistec suggests upgrading the rods. They suggest their W3 turbo mod can deliver more than 1400 hp in the M157 if the engine internals are properly addressed.

PTG and TunedMercedes also have options for huge power. And many other people have started to make these big hp numbers on this platform. Many of the world record cars actually use stock internals. As of 10/10/2025 I am under the impression that the current world record holder for M157 is ECC tuned and running stock internals.

Which stage is right for me?

Daily driver, stock hardware, 91–93 fuel? Start with Stage 1.
Have downpipes/intake/cooling and want more? Consider Stage 2.
Upgraded turbos or planning E-mixes? You’re in Stage 3 territory—contact us.
Unsure? Send your VIN, platform, and mods—We’ll recommend a safe plan.

Get a Safe Power Plan

Stage Comparison

Feature	Stage 1	Stage 2	Stage 3
Hardware baseline	Stock	Bolt-ons (DP/intake/cooling)	Upgraded turbos/fueling
Fuel	91–93 AKI	91–93 (E-mix optional per platform)	E-mix/E85 or specialized fuels
Flash method	OBD on many platforms	OBD or bench	OBD or bench
Datalog support	Included	Included	Required (iterative)
Use case	Daily / highway	Spirited / track days	Built setups
Heat strategy	Conservative	Enhanced with bolt-ons	Custom; hardware-dependent