M157 Primary vs Secondary Downpipes: Which Set Your E63, CLS63 or S63 Actually Needs
Short answer: the M157 has two sets of catalytic converters, and "downpipes" can mean either one. The primaries bolt straight to the turbo outlets and hold the biggest restriction in the system — that's the set you want first. The secondaries sit further downstream and are a separate part. Running both is a full decat. Buying the wrong one is the single most common M157 ordering mistake we see.
The 5.5-litre bi-turbo M157 is one of the most tuner-friendly engines Mercedes ever built, and also one of the easiest to buy the wrong exhaust parts for. Two sets of cats, two drivetrain layouts, and a lot of listings that just say "downpipes." Here's how to sort it out in five minutes.
The two sets, and what each one does
Primary downpipes — at the turbo outlets
These bolt directly to the turbochargers. The exhaust gas hits them first, at their hottest and highest velocity, which is exactly where a restriction costs you the most. The factory primaries contain the main catalytic converters.
Replacing them is where the meaningful gain lives: measurably faster spool, sharper throttle, and the flow headroom a calibration needs to make real power. If you only do one thing to an M157 exhaust, do this one.
Secondary sections — further downstream
Further back sits a second set of converters. They're smaller, they see cooler and slower gas, and their contribution to total backpressure is proportionally less. Deleting them opens the last real bottleneck between the turbos and the cat-back.
They're worth doing, particularly on a car already running primaries and a tune, where the rest of the system has been opened up and the secondaries become the remaining choke point. But as a first purchase they're the smaller move.
Which order to buy them in
- Primaries first. Biggest restriction, biggest change, and the part a Stage 2 calibration is written around.
- Calibration with them. Without it you get spool and sound and very little power — see what each half is actually worth.
- Secondaries when you want the full path. They stack with the primaries rather than duplicating them.
They address different sections of the same exhaust, so there's no conflict in running both. That's the full decat, and it's where the M157 platform genuinely wakes up.
Now the part that catches people out: RWD or 4MATIC
This decides fitment, and it isn't optional information.
All-wheel-drive M157 cars route a front driveshaft through the area the downpipes occupy. The pipes are shaped around it. A rear-wheel-drive car has no such shaft and its downpipes take a different path. The two are not interchangeable, and no amount of persuasion will make one fit the other car.
For US-market cars, the split is clean:
| Car | Years | Drivetrain |
|---|---|---|
| E63 AMG (W212) | 2012–2013 | Rear-wheel drive |
| CLS63 AMG (C218) | 2012–2013 | Rear-wheel drive |
| E63 S AMG (W212) | 2014–2017 | 4MATIC |
| CLS63 S AMG (C218) | 2014–2018 | 4MATIC |
The 2014 facelift is the dividing line. US-spec E63 and CLS63 moved to 4MATIC as standard for the 2014 model year, so a 2013 car is rear-drive and a 2015 car is all-wheel drive. If you're on the boundary, check for a 4MATIC badge and look for driveshafts running to the front wheels.
Shopping the correct set: M157 RWD primaries (2012–2013 E63 / CLS63) or M157 4MATIC primaries (2014+ E63 S / CLS63 S).
The S63 is the same engine, different car
The W222 S63 also runs the M157, but it's a different chassis with its own routing — E-Class or CLS pipes will not fit it. That car takes its own set: S63 AMG W222 M157 downpipes.
This is the general rule for the whole platform, and worth internalising before you order anything: the engine code tells you what family of parts you need, the chassis code tells you which one. Matching only the engine is how people end up with a box of stainless that doesn't line up with anything.
What about the secondaries?
For the CLS63 (C218) we stock the Supersprint secondary sections — part number 849831, built in Italy, and carrying Supersprint's own 36-month warranty, which is longer than the 12-month structural cover on our own hardware.
Supersprint M157 secondary cat delete (CLS63 C218) →
They're built to order with a two to four week lead time, so they're a plan-ahead purchase rather than an impulse one.
Check engine lights, on either set
Both trip the catalyst efficiency monitor, just at different rates. Delete the primaries and the secondaries are still doing some conversion, so the monitor may take longer to fail. Delete the secondaries and the downstream sensors are watching exactly the section you removed, so it trips readily. Either way you end up at P0420 and P0430 on an untuned car.
The fix is a calibration in both cases — the full reasoning is in will catless downpipes throw a check engine light. The matching software is the M157 custom ECU calibration, which covers E63, CLS63, S63, CL63 and ML63.
Quick reference
- "Downpipes" with no qualifier almost always means the primaries at the turbos.
- Primaries = the big gain. Buy these first.
- Secondaries = the finishing move. Stack them on later.
- 2012–2013 US E63 / CLS63 = RWD. 2014 and later = 4MATIC. Different parts.
- S63 W222 = its own set. Same engine, different chassis.
- Both sets need a tune to make power and to clear the light.
Still not certain which one your car takes? Send your VIN to benzunitedparts@gmail.com and we'll confirm drivetrain, chassis and the correct set before you spend anything.