By now you know our philosophy. No “Stage 1, 2, 3.” Just honest conversations about hardware bottlenecks and safe limits.
But every once in a while, a car rolls into our shop that defies expectations. A vehicle that, even before we touch the ECU, is already making more power than it should. We call these freak engines – and today’s CLS63 is exactly that.
Let’s walk through what we found, what we did, and why this particular M157 engine is special.
Blue line: Baseline with customer’s existing mods – 653hp
Red line: Our calibration – 710hp / 1060Nm
The Vehicle: Mercedes‑Benz CLS63 AMG (M157 Engine)
The M157 is a 5.5‑litre twin‑turbo V8. In factory form, it’s rated at 577 horsepower. A healthy, well‑maintained example typically puts down somewhere close to that on our dyno – maybe a little more.
But this particular CLS63 arrived with some thoughtful modifications already installed:
- Improved heat exchanger (to keep intake air temperatures down under higher boost)
- Turbosmart blow‑off valve (better boost control and response)
- Catless downpipes (reduced backpressure, lower exhaust gas temps)
With these mods alone, we expected to see something in the region of 590–600hp based on previous examples we’ve dynoed.
What we actually saw:
659 horsepower at the wheels (or crank – clarify as needed).
That’s 82hp above factory rating from just bolt‑ons. And it’s 60hp higher than other identical‑spec M157s we’ve tested.
This engine is a genuine freak. Sometimes you just get one that rolls off the line with tighter tolerances, better ring seals, or simply a happier disposition. This was one of those.
Our Calibration – Respecting the Stock Bottlenecks
Even though the car was already making exceptional power, we approached the tune with the same discipline we always use:
- We stayed on the factory turbochargers (no upgrade)
- We kept the factory transmission (the M157’s 7‑speed MCT has limits)
- We increased boost and timing safely, monitoring knock, exhaust gas temps, and fuel pressure
Our final result:
710 horsepower and 1060 Newton‑metres of torque.
That’s a gain of 51 horsepower and a substantial increase in torque – all while keeping the factory turbos and gearbox intact.
We could have pushed harder. But respecting the hardware limits is what separates a reliable tune from a blown engine or a fried transmission.
710hp CLS63 pull: Watch the M157 freak engine sing. (Link to video)
Why We Stopped at 710hp (Factory Turbo & Transmission Limits)
The factory turbos on the M157 are robust, but they have a ceiling. Beyond 710–720hp, the compressor wheels start to overspeed and efficiency drops off sharply. More boost just adds heat, not power.
The transmission is another consideration. The MCT 7‑speed can handle a fair amount of torque, but we know from experience that repeatedly exceeding 1100Nm on stock internals can lead to clutch pack wear or torque converter issues.
To go beyond 710hp safely, you would need:
- Upgraded turbochargers (larger wheels or hybrid units)
- Transmission build (clutch packs, torque converter, or software recalibration)
- Supporting fuel system upgrades (the M157’s HPFP and injectors start to struggle above 720hp)
We are not saying it’s impossible – but it would no longer be a “stock hardware” tune. And we won’t pretend otherwise.
The “Freak Engine” Caveat
It’s important to be honest with our customers: Not every CLS63 will make 710hp with these same mods and our tune.
Most M157s with a heat exchanger, BOV, and catless downpipes will land in the 595–605hp range before tuning. After our calibration, those same cars typically finish around 640–660hp.
This particular car started at 659hp (already freakish) and ended at 710hp. That’s an outlier – a beautiful one, but an outlier.
If you own an M157 and you’re expecting 710hp, we will not promise that. We will promise to give you the safest, strongest calibration your specific engine can handle – whether that’s 640hp or 710hp.
The Bottom Line (For M157 CLS63 / E63 / GLE63 Owners)
| Power Level | Required Hardware | Notes |
|---|---|---|
| 577hp | Completely stock | Factory rating |
| 595–605hp | Heat exchanger + BOV + catless downpipes (no tune yet) | Typical baseline for these bolt‑ons |
| 640–660hp | Same bolt‑ons + our calibration | Typical outcome for most M157s |
| 710hp / 1060Nm | Same bolt‑ons + our calibration | Freak engine – not guaranteed, but possible |
| 720hp+ | Upgraded turbos + transmission build + fuel system | Beyond stock hardware limits |
No stages. Just honest numbers and realistic expectations.
Ready for Your M157?
If you own a CLS63, E63, GLE63, or any other M157‑powered Mercedes and you want:
- A safe, maximum‑effort tune on your current hardware
- An honest assessment of whether your engine is a “freak” or normal
- A clear path to 720hp+ (turbo upgrades, transmission build, etc.)
…reach out. We’ll give you a no‑BS recommendation based on your actual car.
No stage kits. No overpromises. Just the right solution for your specific bottleneck – whether that’s 660hp or 710hp.